This study was supported by grants for scientific research (P01 HL116264, RO1 HL137748). The authors would like to thank Theresa Kurth for her advice and help in maintaining the experimental environment as the lab manager.

The protocol is approved by the Medical College of Wisconsin Institutional Animal Care and Use. Dahl salt-sensitive rats (males and females), ~8 weeks of age, 200-350 g, were used for the experiments.
1. Animal preparation
<ol>
	<li>Install a movement response caging system for the rat, a perivascular flow module, syringe pump, recording device, and software (see Table of Materials) in the animal room.</li>
	<li>Place the rats in the cage to become familiar with the environment, food, and water system at least the week prior to surgery. Fast the rats from the day before the surgery because a high stomach content may interfere with the placement of the flow probe into the left renal artery and can cause tracheal aspiration.</li>
	<li>Connect a 5 cm of polyurethane tubing (inner diameter 0.30 mm and outer diameter 0.64 mm) to the end of the 90 cm of polyurethane tubing (inner diameter 0.64 mm and outer diameter 1.02 mm) with PVC cement to make a femoral arterial catheter (see Table of Materials).
	<ol>
		<li>Sterilize the catheters with an Ethylene oxide sterilizer, the flow probe with 2.5% glutaraldehyde, and the surgical instruments in a steam autoclave. Wipe surgical tables, microscopy, and lights with 1% sodium hypochlorite.</li>
	</ol>
	</li>
</ol>
2. Surgery
<ol>
	<li>Place the RBF probe following the steps below.
	<ol>
		<li>Anesthetize the rats with 2.0%-2.5% Isoflurane to the degree that the rats do not respond to the pain stimulus. Place it on the surgical table set at 37 &#176;C and inject 0.09 mg/kg of buprenorphine SR and 15 mg/kg of cefazolin (see Table of Materials) before surgery.</li>
		<li>Shave the entire abdomen with an electric clipper and a region on the nape of the neck around the 7th cervical vertebrae where the catheter and flow prove wires will exit.</li>
		<li>After shaving, wipe the area with 70% ethanol, 10% povidone-iodine, and again with 70% ethanol.</li>
		<li>Place the rat in the prone position. Make a 1 cm cut using a scalpel on the nape of the neck and the left flank. Then, perform a blunt dissection with hemostatic forceps and clear a subcutaneous space from the flank incision to the back of the neck.</li>
		<li>Pass the flow probe through this subcutaneous tunnel from the neck to the flank incision with hemostatic forceps.</li>
		<li>Place the rat in the supine position. Make a 4-5 cm midline abdominal incision.</li>
		<li>Dissect the area around the renal artery with curved tweezers to expose a space sufficient to place the flow probe (see Table of Materials). Then bluntly pierce the left quadratus lumborum muscle with the hemostatic forceps and pull the head of the flow probe into the abdominal cavity.</li>
		<li>Hook the tip of the flow probe to the left renal artery and connect it to the flow meter (see Table of Materials). Add some gel around the probe tip, and the value of the flow rate will appear on the flow meter. 
		NOTE: Although it depends on the size of the rat, a flow of about 3-5 mL/min will be observed in a 230 g rat.</li>
		<li>Glue the polyester fiber mesh attached to the probe with tissue adhesive to the abdominal wall and hold until dry and bonded (~1-2 min). Once the flow is in place, disconnect the flow probe from the flow meter and cover the abdomen with saline-soaked gauze and move on to the step of inserting the catheter.</li>
	</ol>
	</li>
	<li>Insert the femoral catheter following the steps below. 
	NOTE: The method for inserting a fluid-filled catheter is the same as regular telemetry installations. Although telemetry is preferred, the arterial catheter enables pressure monitoring and period blood sampling from the conscious rat.
	<ol>
		<li>First, fill the catheter with saline and clamp it with vascular forceps before making a 1 cm skin incision using a scalpel on the left thigh to dissect and expose the femoral artery. While blocking the flow at the proximal side of the femoral artery with a thread, insert the catheter.</li>
		<li>Flush with a small amount of saline, plug with appropriate size stainless wire, and tie the catheter with a thread to fix it.</li>
		<li>Once the ligature is tied around the catheter, create a subcutaneous tunnel by using a stainless-steel trocar from the thigh to the back of the neck to bring the catheter to the neck region. Secure it with 3-0 silk sutures placed in the trapezius muscle.</li>
	</ol>
	</li>
	<li>Suture the probe.
	<ol>
		<li>Turn the rat to the prone position and stitch the circular loop of the flow probe subcutaneously at the flank. Suture the incision at the flank and the neck with 4-0 surgical suture (see Table of Materials).</li>
		<li>Attach a skin button to the flow probe and suture it with 3-0 silk at the back of the neck.</li>
		<li>Connect the flow probe to the flow meter again, turn the rat back to the dorsal position to check RBF, and make final adjustments of the flow probe to optimize its position on the renal artery.</li>
		<li>Finally, suture the muscle with 3-0 silk and the skin with 4-0 surgical suture.</li>
	</ol>
	</li>
</ol>
3. Recovery of the animal
<ol>
	<li>After careful observation, until the rats are fully recovered from the anesthesia, return the rats to a movement response caging system, connect the flow probe to the blood flow meter, and allow a recovery period of about a week to stabilize the probe and flow measurement. 
	NOTE: Recording doesn&#39;t have to be done during this period.</li>
	<li>Infuse 3% heparinized saline continuously throughout the study from the arterial catheter at the rate of 100 &#181;L/h to prevent the clotting.</li>
	<li>When the flow stabilizes after 5-6 days, set the flowmeter calibration to measure blood flow at 0-20 mL/min and begin the continuous recording of RBF.</li>
</ol>

<ol><li>Chonchol, M., Smogorzewski, M., Stubbs, J., Yu, A. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aChonchol%2C+M+%22Brenner+%26+Rector%27s+The+Kidney%22">Brenner & Rector's The Kidney</a>. 11, Elsevier Inc. Philadelphia, PA. (2019).</li>
<li>Chen, J. -K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Phosphatidylinositol+3-kinase+signaling+determines+kidney+size%5BTitle%5D)+AND+%22Journal+of+Clinical+Investigation%22%5BJournal%5D)">Phosphatidylinositol 3-kinase signaling determines kidney size.</a> Journal of Clinical Investigation. 125 (6), 2429-2444 (2015).</li>
<li>Sigmon, D. H., Gonzalez-Feldman, E., Cavasin, M. A., Potter, D. L., Beierwaltes, W. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Role+of+nitric+oxide+in+the+renal+hemodynamic+response+to+unilateral+nephrectomy%5BTitle%5D)+AND+%22Journal+of+the+American+Society+of+Nephrology%22%5BJournal%5D)">Role of nitric oxide in the renal hemodynamic response to unilateral nephrectomy.</a> Journal of the American Society of Nephrology. 15 (6), 1413-1420 (2004).</li>
<li>Romero, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Noninvasive+measurement+of+renal+blood+flow+by+magnetic+resonance+imaging+in+rats%5BTitle%5D)+AND+%22American+Journal+of+Physiology-Renal+Physiology%22%5BJournal%5D)">Noninvasive measurement of renal blood flow by magnetic resonance imaging in rats.</a> American Journal of Physiology-Renal Physiology. 314 (1), 99-106 (2018).</li>
<li>Basile, D. P., Anderson, M. D., Sutton, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Pathophysiology+of+acute+kidney+injury%5BTitle%5D)+AND+%22Comprehensive+Physiology%22%5BJournal%5D)">Pathophysiology of acute kidney injury.</a> Comprehensive Physiology. 2 (2), 1303-1353 (2012).</li>
<li>Regan, M. C., Young, L. S., Geraghty, J., Fitzpatrick, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Regional+renal+blood+flow+in+normal+and+disease+states%5BTitle%5D)+AND+%22Urological+Research%22%5BJournal%5D)">Regional renal blood flow in normal and disease states.</a> Urological Research. 23 (1), 1-10 (1995).</li>
<li>Ter Wee, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effects+of+calcium+antagonists+on+renal+hemodynamics+and+progression+of+nondiabetic+chronic+renal+disease%5BTitle%5D)+AND+%22Archives+of+Internal+Medicine%22%5BJournal%5D)">Effects of calcium antagonists on renal hemodynamics and progression of nondiabetic chronic renal disease.</a> Archives of Internal Medicine. 154 (11), 1185(1994).</li>
<li>Mazze, R. I., Cousins, M. J., Barr, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Renal+effects+and+metabolism+of+isoflurane+in+man%5BTitle%5D)+AND+%22Anesthesiology%22%5BJournal%5D)">Renal effects and metabolism of isoflurane in man.</a> Anesthesiology. 40 (6), 536-542 (1974).</li>
<li>Corrigan, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((PAH+extraction+and+estimation+of+plasma+flow+in+human+postischemic+acute+renal+failure%5BTitle%5D)+AND+%22American+Journal+of+Physiology-Renal+Physiology%22%5BJournal%5D)">PAH extraction and estimation of plasma flow in human postischemic acute renal failure.</a> American Journal of Physiology-Renal Physiology. 277 (2), 312-318 (1999).</li>
<li>Laroute, V., Lefebvre, H. P., Costes, G., Toutain, P. -L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Measurement+of+glomerular+filtration+rate+and+effective+renal+plasma+flow+in+the+conscious+beagle+dog+by+single+intravenous+bolus+of+iohexol+and+p-aminohippuric+acid%5BTitle%5D)+AND+%22Journal+of+Pharmacological+and+Toxicological+Methods%22%5BJournal%5D)">Measurement of glomerular filtration rate and effective renal plasma flow in the conscious beagle dog by single intravenous bolus of iohexol and p-aminohippuric acid.</a> Journal of Pharmacological and Toxicological Methods. 41 (1), 17-25 (1999).</li>
<li>Wei, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Quantification+of+renal+blood+flow+with+contrast-enhanced+ultrasound%5BTitle%5D)+AND+%22Journal+of+the+American+College+of+Cardiology%22%5BJournal%5D)">Quantification of renal blood flow with contrast-enhanced ultrasound.</a> Journal of the American College of Cardiology. 37 (4), 1135-1140 (2001).</li>
<li>Cao, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Contrast-enhanced+ultrasound+for+assessing+renal+perfusion+impairment+and+predicting+acute+kidney+injury+to+chronic+kidney+disease+progression%5BTitle%5D)+AND+%22Antioxidants+%26+Redox+Signaling%22%5BJournal%5D)">Contrast-enhanced ultrasound for assessing renal perfusion impairment and predicting acute kidney injury to chronic kidney disease progression.</a> Antioxidants & Redox Signaling. 27 (17), 1397-1411 (2017).</li>
<li>Markl, M., Frydrychowicz, A., Kozerke, S., Hope, M., Wieben, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((4D+flow+MRI%5BTitle%5D)+AND+%22Journal+of+Magnetic+Resonance+Imaging%22%5BJournal%5D)">4D flow MRI.</a> Journal of Magnetic Resonance Imaging. 36 (5), 1015-1036 (2012).</li>
<li>Juillard, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Dynamic+renal+blood+flow+measurement+by+positron+emission+tomography+in+patients+with+CRF%5BTitle%5D)+AND+%22American+Journal+of+Kidney+Diseases%22%5BJournal%5D)">Dynamic renal blood flow measurement by positron emission tomography in patients with CRF.</a> American Journal of Kidney Diseases. 40 (5), 947-954 (2002).</li>
<li>Juárez-Orozco, L. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Imaging+of+cardiac+and+renal+perfusion+in+a+rat+model+with+13N-NH3+micro-PET%5BTitle%5D)+AND+%22The+International+Journal+of+Cardiovascular+Imaging%22%5BJournal%5D)">Imaging of cardiac and renal perfusion in a rat model with 13N-NH3 micro-PET.</a> The International Journal of Cardiovascular Imaging. 31 (1), 213-219 (2015).</li>
<li>Mori, T., Cowley, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Role+of+pressure+in+angiotensin+II-induced+renal+injury%5BTitle%5D)+AND+%22Hypertension%22%5BJournal%5D)">Role of pressure in angiotensin II-induced renal injury.</a> Hypertension. 43 (4), 752-759 (2004).</li>
<li>Mori, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High+perfusion+pressure+accelerates+renal+injury+in+salt-sensitive+hypertension%5BTitle%5D)+AND+%22Journal+of+the+American+Society+of+Nephrology%22%5BJournal%5D)">High perfusion pressure accelerates renal injury in salt-sensitive hypertension.</a> Journal of the American Society of Nephrology. 19 (8), 1472-1482 (2008).</li>
<li>Polichnowski, A. J., Cowley, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Pressure-induced+renal+injury+in+angiotensin+II+versus+norepinephrine-induced+hypertensive+rats%5BTitle%5D)+AND+%22Hypertension%22%5BJournal%5D)">Pressure-induced renal injury in angiotensin II versus norepinephrine-induced hypertensive rats.</a> Hypertension. 54 (6), 1269-1277 (2009).</li>
<li>Polichnowski, A. J., Jin, C., Yang, C., Cowley, A. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Role+of+renal+perfusion+pressure+versus+angiotensin+II+renal+oxidative+stress+in+angiotensin+II-induced+hypertensive+rats%5BTitle%5D)+AND+%22Hypertension%22%5BJournal%5D)">Role of renal perfusion pressure versus angiotensin II renal oxidative stress in angiotensin II-induced hypertensive rats.</a> Hypertension. 55 (6), 1425-1430 (2010).</li>
<li>Evans, L. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Increased+perfusion+pressure+drives+renal+T-cell+infiltration+in+the+dahl+salt-sensitive+rat%5BTitle%5D)+AND+%22Hypertension%22%5BJournal%5D)">Increased perfusion pressure drives renal T-cell infiltration in the dahl salt-sensitive rat.</a> Hypertension. 70 (3), 543-551 (2017).</li>
<li>Shimada, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Renal+perfusion+pressure+determines+infiltration+of+leukocytes+in+the+kidney+of+rats+with+angiotensin+II-induced+hypertension%5BTitle%5D)+AND+%22Hypertension%22%5BJournal%5D)">Renal perfusion pressure determines infiltration of leukocytes in the kidney of rats with angiotensin II-induced hypertension.</a> Hypertension. 76 (3), 849-858 (2020).</li>
<li>Cousins, M. J., Mazze, R. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Anaesthesia%2C+surgery+and+renal+function%3A+Immediate+and+delayed+effects%5BTitle%5D)+AND+%22Anaesthesia+and+Intensive+Care%22%5BJournal%5D)">Anaesthesia, surgery and renal function: Immediate and delayed effects.</a> Anaesthesia and Intensive Care. 1 (5), 355-373 (1973).</li>
<li>Cousins, M. J., Skowronski, G., Plummer, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Anaesthesia+and+the+kidney%5BTitle%5D)+AND+%22Anaesthesia+and+Intensive+Care%22%5BJournal%5D)">Anaesthesia and the kidney.</a> Anaesthesia and Intensive Care. 11 (4), 292-320 (1983).</li>
<li>Schiffer, T. A., Christensen, M., Gustafsson, H., Palm, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+effect+of+inactin+on+kidney+mitochondrial+function+and+production+of+reactive+oxygen+species%5BTitle%5D)+AND+%22PLOS+ONE%22%5BJournal%5D)">The effect of inactin on kidney mitochondrial function and production of reactive oxygen species.</a> PLOS ONE. 13 (11), 0207728(2018).</li>
<li>Evans, R. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Chronic+renal+blood+flow+measurement+in+dogs+by+transit-time+ultrasound+flowmetry%5BTitle%5D)+AND+%22Journal+of+Pharmacological+and+Toxicological+Methods%22%5BJournal%5D)">Chronic renal blood flow measurement in dogs by transit-time ultrasound flowmetry.</a> Journal of Pharmacological and Toxicological Methods. 38 (1), 33-39 (1997).</li>
<li>Bell, T. D., DiBona, G. F., Biemiller, R., Brands, M. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Continuously+measured+renal+blood+flow+does+not+increase+in+diabetes+if+nitric+oxide+synthesis+is+blocked%5BTitle%5D)+AND+%22American+Journal+of+Physiology-Renal+Physiology%22%5BJournal%5D)">Continuously measured renal blood flow does not increase in diabetes if nitric oxide synthesis is blocked.</a> American Journal of Physiology-Renal Physiology. 295 (5), 1449-1456 (2008).</li>
</ol>

The authors have nothing to disclose.

The present protocol describes a technique that utilizes commercially available instrumentation to record RBF and arterial pressure continuously over many weeks. In addition, urine can be collected using the device described in step 1.1. It can also be used to evaluate metabolites in the urine and, when an arterial catheter is implanted, blood sampling for analysis.
Traditionally, RBF measurements have been obtained acutely in surgically prepared anesthetized animals or estimated by PAH cleara...

The kidneys are only 0.5% of the bodyweight but rich in blood flow, receiving 20%-25% of the total cardiac output1. The regulation of renal blood flow (RBF) is central to kidney function, body fluid, and electrolyte homeostasis. The importance of blood flow regulation to the kidney is nicely illustrated by the substantial increase of RBF in the remaining kidney after unilateral nephrectomy2,3,4 and by the reductions of RBF that occur in kidney failure5,6,7. Whether such changes in RBF occur in response to alterations in kidney function or a decrease in function due to reduction of RBF has been challenging to ascertain in anesthetized surgically prepared animals or human subjects. Temporal studies are required in which the events can be determined before and following a defined change and observed in the same animal during the progression of events. In the animal and human studies, RBF has been estimated indirectly by the clearance of para-amino hippuric acid (PAH)8,9,10 and in more recent time by imaging techniques such as ultrasound9,11,12, MRI4,13, and PET-CT14,15 which give helpful snapshot images of each kidney and which can follow the progression of the disease. It is challenging to evaluate RBF in small animals by ultrasound or MRI scans without anesthesia. It has been impossible to continuously measure RBF under conscious conditions in the same rat over prolonged periods.
The present protocol, therefore, developed techniques that enable simultaneous continuous 24 h/day measurements of RBF, which has been combined with continuous blood pressure measurement methods for freely moving rats as described previously16,17,18,19,20,21. This technology allows for the temporal evaluation of RBF in various models of rats to study cause-effect relationships in various renal disorders in the future.

<table><tbody><tr><td>1RB probe</td><td>Transonic</td><td>1RB</td><td>ultrasonic flow probe</td></tr><tr><td>Betadine</td><td>Avrio Health</td><td></td><td>povidone-iodine</td></tr><tr><td>Buprenorphine SR-LAB</td><td>ZooPharm</td><td></td><td>Buprenorphine</td></tr><tr><td>Cefazolin</td><td>APOTEX</td><td>NDC 60505</td><td>Cefazolin</td></tr><tr><td>Crile Hemostats</td><td>Fine Surgical Instruments</td><td>13004-14</td><td>Hemostats for blunt dissection</td></tr><tr><td>Isoflurane</td><td>Piramal</td><td>NDC 66794</td><td>Isoflurane</td></tr><tr><td>Medium Clear PVC cement</td><td>Oatey</td><td></td><td>PVC cement</td></tr><tr><td>Mersilene polyester fiber mesh</td><td>Ethicon</td><td></td><td>polyester fiber mesh</td></tr><tr><td>MetriCide28</td><td>Metrex</td><td>SKU 10-2805</td><td>2.5% glutaraldehyde</td></tr><tr><td>Micro-Renathane 0.025 x 0.012</td><td>Braintree Scientific</td><td>MRE 025</td><td>use for catheter</td></tr><tr><td>MINI HYPE-WIPE</td><td>Current Technologies</td><td>#9803</td><td>1% sodium hypochlorite</td></tr><tr><td>Oatey Medium Clear PVC Cement</td><td>Oatey</td><td>#31018</td><td>PVC cement</td></tr><tr><td>PHD2000 syringe pump</td><td>Harvard apparatus</td><td>71-2000</td><td>syringe pump</td></tr><tr><td>Ponemah software</td><td>DSI</td><td></td><td>recording software</td></tr><tr><td>Precision 3630 Tower</td><td>Dell</td><td></td><td>Computer for recording</td></tr><tr><td>Raturn Stand-Alone System</td><td>BASi</td><td>MD-1407</td><td>a movement response caging system</td></tr><tr><td>RenaPulse High Fidelity Pressure Tubing 0.040 x 0.025</td><td>Braintree Scientific</td><td>RPT 040</td><td>use for catheter</td></tr><tr><td>Silicone cuff</td><td>Transonic</td><td>AAPC102</td><td>skin button</td></tr><tr><td>Surgical lubricant sterile bacteriostatic</td><td>Fougera</td><td>0168-0205-36</td><td>gell for flow probe</td></tr><tr><td>Tergazyme</td><td>Alconox</td><td></td><td>protease contained anionic detergent</td></tr><tr><td>TS420 Perivascular Flow Module</td><td>Transonic</td><td>TS420</td><td>perivascular flow module</td></tr><tr><td>Vetbond</td><td>3M</td><td>1469SB</td><td>tissue adhesive</td></tr><tr><td>WinDaq software</td><td>DATAQ</td><td></td><td>recording software</td></tr></tbody></table>

long-term continuous measurement of renal blood flow in conscious rats

The kidneys play a crucial role in maintaining the homeostasis of body fluids. The regulation of renal blood flow (RBF) is essential to the vital functions of filtration and metabolism in kidney function. Many acute studies have been carried out in anesthetized animals to measure RBF under various conditions to determine mechanisms responsible for the regulation of kidney perfusion. However, for technical reasons, it has not been possible to measure RBF continuously (24 h/day) in unrestrained unanesthetized rats over prolonged periods. These methods allow the continuous determination of RBF over many weeks while also simultaneously recording blood pressure (BP) with implanted catheters (fluid-filled or by telemetry). RBF monitoring is carried out with rats placed in a circular servo-controlled rat cage that enables the unrestrained movement of the rat throughout the study. At the same time, the tangling of cables from the flow probe and arterial catheters is prevented. Rats are first instrumented with an ultrasonic flow probe placement on the left renal artery and an arterial catheter implanted in the right femoral artery. These are routed subcutaneously to the nape of the neck, and connected to the flowmeter and pressure transducer, respectively, to measure RBF and BP. Following surgical implantation, rats are immediately placed in the cage to recover for at least one week and stabilize the ultrasonic probe recordings. Urine collection is also feasible in this system. The surgical and post-surgical procedures for continuous monitoring are demonstrated in this protocol.

The mean arterial pressure data (Figure 1A) and blood flow data (Figure 1B) from a representative male Dahl salt-sensitive rat are shown. The Dahl salt-sensitive rats are maintained in a colony and bred at the Medical College of Wisconsin. The surgery was done at the age of 8 weeks, and the bodyweight was 249 g at the time of surgery. Rats were fed with a 0.4% NaCl diet, and the diet was changed to a 4% NaCl diet at the age of 10 weeks. Measurements were continu...

Watch this Scientific Journal Video about Long-Term Continuous Measurement of Renal Blood Flow in Conscious Rats at JoVE.com

Long-Term Continuous Measurement of Renal Blood Flow in Conscious Rats

The present protocol describes a long-term continuous measurement of renal blood flow in conscious rats and simultaneously recording blood pressure with implanted catheters (fluid-filled or by telemetry).

The kidneys play a crucial role in maintaining the homeostasis of body fluids. The regulation of renal blood flow (RBF) is essential to the vital ...

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2.5K Views.  Medical College of Wisconsin. De continue registratie van de renale bloedstroom bij geïnstrumenteerde ratten stelt ons in staat om tijdelijk de volgorde van gebeurtenissen te bepalen die leiden tot het ziekteproces dat we bestuderen. In ons geval is het hypertensie en we proberen te bepalen of een vermindering van de renale bloedstroom, die optreedt bij hypertensie, voorafgaat aan of een gevolg is van de hoge bloeddruk. Het systeem dat we vandaag zullen demonstreren en de voorbereiding van het dier is echt ontworpen om e...

Video: Long-Term Continuous Measurement of Renal Blood Flow in Conscious Rats

Femoral Arterial and Venous Catheterization for Blood Sampling, Drug Administration and Conscious Blood Pressure and Heart Rate Measurements

In multiple fields of study, access to the circulatory system in laboratory studies is necessary. Pharmacological studies in rats using chronically implanted catheters permit a researcher to effectively and humanely administer substances, perform repeated blood sampling and assists in conscious direct measurements of blood pressure and heart rate. Once the catheter is implanted long-term sampling is possible. Patency and catheter life depends on multiple factors including the lock solution used, flushing regimen and catheter material. This video will demonstrate the methodology of femoral artery and venous catheterization of the rat. In addition the video will demonstrate the use of the femoral venous and arterial catheters for blood sampling, drug administration and use of the arterial catheter in taking measurements of blood pressure and heart rate in a conscious freely-moving rat. A tether and harness attached to a swivel system will allow the animal to be housed and have samples taken by the researcher with minimal disruption to the animal. To maintain patency of the catheter, careful daily maintenance of the catheter is required using lock solution (100 U/ml heparinized saline), machine-ground blunt tip syringe needles and the use of syringe filters to minimize potential contamination. With careful aseptic surgical techniques, proper catheter materials and careful catheter maintenance techniques, it is possible to sustain patent catheters and healthy animals for long periods of time (several weeks).

Chronic catheterization of blood vessels in the rat is often required for administration of substances, obtain blood sample over a period of time or for direct conscious blood pressure measurements. Femoral arterial catheterization of the rat and corresponding measurements of blood pressure in the conscious animal will be demonstrated.

In multiple fields of study, access to the circulatory system in laboratory studies is necessary. Pharmacological studies in rats using chronically ...

Automated Measurement of Microcirculatory Blood Flow Velocity in Pulmonary Metastases of Rats

Because the lung is a major target organ of metastatic disease, animal models to study the physiology of pulmonary metastases are of great importance. However, very few methods exist to date to investigate lung metastases in a dynamic fashion at the microcirculatory level, due to the difficulty to access the lung with a microscope. Here, an intravital microscopy method is presented to functionally image and quantify the microcirculation of superficial pulmonary metastases in rats, using a closed-chest pulmonary window and automated analysis of blood flow velocity and direction. The utility of this method is demonstrated to measure increases in blood flow velocity in response to pharmacological intervention, and to image the well-known tortuous vasculature of solid tumors. This is the first demonstration of intravital microscopy on pulmonary metastases in a closed-chest model. Because of its minimized invasiveness, as well as due to its relative ease and practicality, this technology has the potential to experience widespread use in laboratories that specialize on pulmonary tumor research.

A method is presented to measure microcirculatory blood flow velocity in pulmonary cancer metastases of the pleural surface in rats in an automated fashion, using closed-chest pulmonary intravital microscopy. This model has potential to be used as a widespread tool to perform physiologic research on pulmonary metastases in rodents.

Because the lung is a major target organ of metastatic disease, animal models to study the physiology of pulmonary metastases are of great importance. ...

Early Detection of Drug-Induced Renal Hemodynamic Dysfunction Using Sonographic Technology in Rats

The kidney normally functions to maintain hemodynamic homeostasis and is a major site of damage caused by drug toxicity. Drug-induced nephrotoxicity is estimated to contribute to 19- 25% of all clinical cases of acute kidney injury (AKI) in critically ill patients. AKI detection has historically relied on metrics such as serum creatinine (sCr) or blood urea nitrogen (BUN) which are demonstrably inadequate in full assessment of nephrotoxicity in the early phase of renal dysfunction. Currently, there is no robust diagnostic method to accurately detect hemodynamic alteration in the early phase of AKI while such alterations might actually precede the rise in serum biomarker levels. Such early detection can help clinicians make an accurate diagnosis and help in in decision making for therapeutic strategy. Rats were treated with Cisplatin to induce AKI. Nephrotoxicity was assessed for six days using high-frequency sonography, sCr measurement and upon histopathology of kidney. Hemodynamic evaluation using 2D and Color-Doppler images were used to serially study nephrotoxicity in rats, using the sonography. Our data showed successful drug-induced kidney injury in adult rats by histological examination. Color-Doppler based sonographic assessment of AKI indicated that resistive-index (RI) and pulsatile-index (PI) were increased in the treatment group; and peak-systolic velocity (mm/s), end-diastolic velocity (mm/s) and velocity-time integral (VTI, mm) were decreased in renal arteries in the same group. Importantly, these hemodynamic changes evaluated by sonography preceded the rise of sCr levels. Sonography-based indices such as RI or PI can thus be useful predictive markers of declining renal function in rodents. From our sonography-based observations in the kidneys of rats that underwent AKI, we showed that these noninvasive hemodynamic measurements may consider as an accurate, sensitive and robust method in detecting early stage kidney dysfunction. This study also underscores the importance of ethical issues associated with animal use in research.

Early stage hemodynamic dysfunction is critical to the development of kidney disease. Yet, detection methodologies are limited. Recent advances in sonography provide a noninvasive, accurate option for early detection of kidney injury. This study outlines a step-by-step, sonographic methodology for detecting kidney dysfunction using a drug-induced nephrotoxicity rat model.

The kidney normally functions to maintain hemodynamic homeostasis and is a major site of damage caused by drug toxicity. Drug-induced nephrotoxicity is ...

Transcutaneous Assessment of Renal Function in Conscious Rodents

Glomerular filtration rate (GFR) is the gold standard to assess overall kidney function. However, traditional methods to evaluate GFR are cumbersome and time-consuming. In addition, serial blood or urine samples are required, with the associated stress for the experimental animals. A recent technique significantly reduces the investment in time and resources, minimizing the invasiveness and the animal stress, but being equally valid as the traditional approaches. The method measures transcutaneously renal function. Using an optical device and the exogenous renal marker fluorescein isothiocyanate (FITC)-sinistrin, this technique is capable of measuring the elimination kinetics of the marker through the skin. With neither blood nor urine samples nor the associated laboratory assays needed, the results of the transcutaneous measurement are almost instantaneously available. The method has been already validated in different species and successfully applied in several models of renal pathology. Moreover, due to its minimally invasive characteristics, it is suitable for sequential measurements within the same animal. Here is provided a detailed protocol to carry out the transcutaneous assessment of renal function in rodents.

Determination of glomerular filtration rate (GFR) is the gold standard to assess overall kidney function. However, traditional procedures to measure this parameter are cumbersome and require a large investment of time. Here we describe a faster and minimally invasive method to determinate GFR transcutaneously.

Glomerular filtration rate (GFR) is the gold standard to assess overall kidney function. However, traditional methods to evaluate GFR are cumbersome and ...

Novel Approach for Simultaneous Recording of Renal Sympathetic Nerve Activity and Blood Pressure with Intravenous Infusion in Conscious, Unrestrained Mice.

Renal sympathetic nerves contribute significantly to both physiological and pathophysiological phenomena. Evaluating renal sympathetic nerve activity (RSNA) is of great interest in many areas of research such as chronic kidney disease, hypertension, heart failure, diabetes and obesity. Unequivocal assessment of the role of the sympathetic nervous system is thus imperative for proper interpretation of experimental results and understanding of disease processes. RSNA has been traditionally measured in anesthetized rodents, including mice. However, mice usually exhibit very low systemic blood pressure and hemodynamic instability for several hours during anesthesia and surgery. Meaningful interpretation of RSNA is confounded by this non-physiological state, given the intimate relationship between sympathetic nervous tone and cardiovascular status. To address this limitation of traditional approaches, we developed a new method for measuring RSNA in conscious, freely-moving mice. Mice were chronically instrumented with radio-telemeters for continuous monitoring of blood pressure as well as a jugular venous infusion catheter and custom-designed bipolar electrode for direct recording of RSNA. Following a 48-72 hour recovery period, survival rate was 100% and all mice behaved normally. At this time-point, RSNA was successfully recorded in 80% of mice, with viable signals acquired up to 4 and 5 days post-surgery in 70% and 50% of mice, respectively. Physiological blood pressures were recorded in all mice (116&plusmn;2 mmHg; n=10). Recorded RSNA increased with eating and grooming, as well-established in the literature. Furthermore, RSNA was validated by ganglionic blockade and modulation of blood pressure with pharmacological agents. Herein, an effective and manageable method for clear recording of RSNA in conscious, freely-moving mice is described.

Anesthetized mice exhibit non-physiological systemic blood pressure, which precludes meaningful assessment of autonomic tone given the intimate relationship between blood pressure and the autonomic nervous system. Thus, a novel method to simultaneously record renal sympathetic nerve activity and blood pressure with intravenous infusion in conscious mice is outlined.

Renal sympathetic nerves contribute significantly to both physiological and pathophysiological phenomena. Evaluating renal sympathetic nerve activity ...

A High-throughput Method for Measurement of Glomerular Filtration Rate in Conscious Mice

The measurement of glomerular filtration rate (GFR) is the gold standard in kidney function assessment. Currently, investigators determine GFR by measuring the level of the endogenous biomarker creatinine or exogenously applied radioactive labeled inulin (3H or 14C). Creatinine has the substantial drawback that proximal tubular secretion accounts for ~50% of total renal creatinine excretion and therefore creatinine is not a reliable GFR marker. Depending on the experiment performed, inulin clearance can be determined by an intravenous single bolus injection or continuous infusion (intravenous or osmotic minipump). Both approaches require the collection of plasma or plasma and urine, respectively. Other drawbacks of radioactive labeled inulin include usage of isotopes, time consuming surgical preparation of the animals, and the requirement of a terminal experiment. Here we describe a method which uses a single bolus injection of fluorescein isothiocyanate-(FITC) labeled inulin and the measurement of its fluorescence in 1-2 &mu;l of diluted plasma. By applying a two-compartment model, with 8 blood collections per mouse, it is possible to measure GFR in up to 24 mice per day using a special work-flow protocol. This method only requires brief isoflurane anesthesia with all the blood samples being collected in a non-restrained and awake mouse. Another advantage is that it is possible to follow mice over a period of several months and treatments (i.e. doing paired experiments with dietary changes or drug applications). We hope that this technique of measuring GFR is useful to other investigators studying mouse kidney function and will replace less accurate methods of estimating kidney function, such as plasma creatinine and blood urea nitrogen.

Measurement of glomerular filtration rate (GFR) is the gold standard for kidney function assessment. Here we describe a high-throughput method which allows the determination of GFR in conscious mice by using a single bolus injection, determination of fluorescein isothiocyanate (FITC)-inulin in plasma and calculation of GFR by a two-phase exponential decay model.

The measurement of  glomerular filtration rate (GFR) is the gold standard in kidney function  assessment. Currently, investigators determine GFR by ...

Biology

Transdermal Measurement of Glomerular Filtration Rate in Mice

Transdermal analysis of glomerular filtration rate (GFR) is an established technique that is used to assess renal function in mouse and rat models of acute kidney injury and chronic kidney disease. The measurement system consists of a miniaturized fluorescence detector that is directly attached to the skin on the back of conscious, freely moving animals, and measures the excretion kinetics of the exogenous GFR tracer, fluorescein-isothiocyanate (FITC) conjugated sinistrin (an inulin analog). This system has been described in detail in rats. However, because of their smaller size, measurement of transcutaneous GFR in mice presents additional technical challenges. In this paper we therefore provide the first detailed practical guide to the use of transdermal GFR monitors in mice based on the combined experience of three different investigators who have been performing this assay in mice over a number of years.

Here we describe a protocol to measure glomerular filtration rate (GFR) in conscious, freely moving mice using a transdermal GFR monitor.

Transdermal analysis of glomerular filtration rate (GFR) is an established technique that is used to assess renal function in mouse and rat models of ...

Simultaneous Electrocardiography Recording and Invasive Blood Pressure Measurement in Rats

For studies related to cardiovascular physiology or pathophysiology, blood pressure (BP) and electrocardiography are basic observational parameters. Research focusing on cardiovascular disease models, potential cardiovascular therapeutic targets or pharmaceutical agents requires assessment of systemic arterial pressure and heart rhythm changes. In situations where radio telemetry systems are not available or affordable, the technique of femoral artery cannulation is an alternative way to obtain intra-arterial pressure waveform recordings and systemic BP measurements. This technique is economical and can be performed with standard equipment in animal facilities. However, invasive arterial pressure recording requires cannulation of small arteries, which can be a challenging surgical skill. Here, we present step-by-step protocols for femoral artery cannulation procedures. Key procedures include the calibration of the data acquisition system, tissue dissection and femoral artery cannulation, and setup of the arterial cannulation system for pressure recording. Surface electrocardiography recording procedures are also included. We also present examples of BP recordings from normotensive and hypertensive rats. This protocol allows reliable direct recordings of systemic BP with simultaneous electrocardiography.

Here, we describe a setup for simultaneous recording of electrocardiography and intra-arterial blood pressure (BP) in experimental rats, which can be done with standard equipment in animal facilities and can be applied to physiological or pharmacological studies to investigate pathogenic or therapeutic mechanisms in cardiovascular medicine.

For studies related to cardiovascular physiology or pathophysiology, blood pressure (BP) and electrocardiography are basic observational parameters. ...

Continuous Blood Sampling in Small Animal Positron Emission Tomography/Computed Tomography Enables the Measurement of the Arterial Input Function

For quantitative analysis and bio-kinetic modeling of positron emission tomography/computed tomography (PET/CT) data, the determination of the temporal blood time-activity concentration also known as arterial input function (AIF) is a key point, especially for the characterization of animal disease models and the introduction of newly developed radiotracers. The knowledge of radiotracer availability in the blood helps to interpret PET/CT-derived data of tissue activity. For this purpose, online blood sampling during the PET/CT imaging is advisable to measure the AIF. In contrast to manual blood sampling and image-derived approaches, continuous online blood sampling has several advantages. Besides the minimized blood loss, there is an improved resolution and a superior accuracy for the blood activity measurement. However, the major drawback of online blood sampling is the costly and time-consuming preparation to catheterize the femoral vessels of the animal. Here, we describe an easy and complete workflow for catheterization and continuous blood sampling during small animal PET/CT imaging and compared it to manual blood sampling and an image-derived approach. Using this highly-standardized workflow, the determination of the fluorodeoxyglucose ([18F]FDG) AIF is demonstrated. Further, this procedure can be applied to any radiotracer in combination with different animal models to create fundamental knowledge of tracer kinetic and model characteristics. This allows a more precise evaluation of the behavior of pharmaceuticals, both for diagnostic and therapeutic approaches in the preclinical research of oncological, neurodegenerative and myocardial diseases.

Here a protocol for continuous blood sampling during PET/CT imaging of rats to measure the arterial input function (AIF) is described. The catheterization, the calibration and setup of the system and the data analysis of the blood radioactivity are demonstrated. The generated data provide input parameters for subsequent bio-kinetic modeling.

For quantitative analysis and bio-kinetic modeling of positron emission tomography/computed tomography (PET/CT) data, the determination of the temporal ...

Physiology Lab Demonstration: Glomerular Filtration Rate in a Rat

Measurements of glomerular filtration rate (GFR), and the fractional excretion of sodium (Na) and potassium (K) are critical in assessing renal function in health and disease. GFR is measured as the steady state renal clearance of inulin which is filtered at the glomerulus, but not secreted or reabsorbed along the nephron. The fractional excretion of Na and K can be determined from the concentration of Na and K in plasma and urine. The renal clearance of inulin can be demonstrated in an anesthetized animal which has catheters in the femoral artery, femoral vein and bladder. The equipment and supplies used for this procedure are those commonly available in a research core facility, and thus makes this procedure a practical means for measuring renal function. The purpose of this video is to demonstrate the procedures required to perform a lab demonstration in which renal function is assessed before and after a diuretic drug. The presented technique can be utilized to assess renal function in rat models of renal disease.

The purpose of this protocol is to demonstrate the principles and techniques for measuring and calculating glomerular filtration rate, urine flow rate, and excretion of sodium and potassium in a rat. This demonstration can be used to provide students with an overall conceptual understanding of how to measure renal function.

Measurements of glomerular filtration rate (GFR), and the fractional excretion of sodium (Na) and potassium (K) are critical in assessing renal function ...

Long-Term Continuous Measurement of Renal Blood Flow in Conscious Rats

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