This work was supported by National Institutes of Health Grants R00 HL112952 (to R. H.), R01 HL108618 (to J.P.G.), P01 HL051971, and P20 GM104357. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

NOTE: All animal procedures were performed according to the NIH Public Health Service Policy on the Human Care and Use of Animals and were approved by the Institutional Animal Care and Use Committee of the University of Mississippi Medical Center. All procedures involving the use of radioisotopes were approved and performed according to the guidelines set by the radiation safety office of the University of Mississippi Medical Center.
1. Preparation of Stock Buffer Solutions and Reagents
<ol>...

<ol>
	<li>Neely, J. R., Morgan, H. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relationship+between+carbohydrate+and+lipid+metabolism+and+the+energy+balance+of+heart+muscle.">Relationship between carbohydrate and lipid metabolism and the energy balance of heart muscle.</a> Annu Rev Physiol. 36, 413-459 (1974).</li><li>Sen, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose+regulation+of+load-induced+mTOR+signaling+and+ER+stress+in+mammalian+heart.">Glucose regulation of load-induced mTOR signaling and ER stress in mammalian heart.</a> J Am Heart Assoc. 2, e004796 (2013).</li><li>Young, M. E., McNulty, P., Taegtmeyer, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adaptation+and+maladaptation+of+the+heart+in+diabetes:+Part+II:+potential+mechanisms.">Adaptation and maladaptation of the heart in diabetes: Part II: potential mechanisms.</a> Circulation. 105, 1861-1870 (2002).</li><li>Stanley, W. C., Recchia, F. A., Lopaschuk, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myocardial+substrate+metabolism+in+the+normal+and+failing+heart.">Myocardial substrate metabolism in the normal and failing heart.</a> Physiol Rev. 85, 1093-1129 (2005).</li><li>Fillmore, N., Lopaschuk, G. 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L., Lopaschuk, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methodology+for+measuring+in+vitro/ex+vivo+cardiac+energy+metabolism.">Methodology for measuring in vitro/ex vivo cardiac energy metabolism.</a> J Pharmacol Toxicol Methods. 43, 141-152 (2000).</li><li>Neely, J. R., Liebermeister, H., Battersby, E. J., Morgan, H. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+pressure+development+on+oxygen+consumption+by+isolated+rat+heart.">Effect of pressure development on oxygen consumption by isolated rat heart.</a> Am J Physiol. 212, 804-814 (1967).</li><li>Taegtmeyer, H., Hems, R., Krebs, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Utilization+of+energy-providing+substrates+in+the+isolated+working+rat+heart.">Utilization of energy-providing substrates in the isolated working rat heart.</a> Biochem J. 186, 701-711 (1980).</li><li>Liao, R., Podesser, B. K., Lim, C. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+continuing+evolution+of+the+Langendorff+and+ejecting+murine+heart:+new+advances+in+cardiac+phenotyping.">The continuing evolution of the Langendorff and ejecting murine heart: new advances in cardiac phenotyping.</a> Am J Physiol Heart Circ Physiol. 303, H156-H167 (2012).</li><li>Cingolani, O. H., Kass, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pressure-volume+relation+analysis+of+mouse+ventricular+function.">Pressure-volume relation analysis of mouse ventricular function.</a> Am J Physiol Heart Circ Physiol. 301, H2198-H2206 (2011).</li><li>Pacher, P., Nagayama, T., Mukhopadhyay, P., Batkai, S., Kass, D. 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G., Guthrie, P. H., Taegtmeyer, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Decreased+long-chain+fatty+acid+oxidation+impairs+postischemic+recovery+of+the+insulin-resistant+rat+heart.">Decreased long-chain fatty acid oxidation impairs postischemic recovery of the insulin-resistant rat heart.</a> FASEB J. 27, 3966-3978 (2013).</li><li>Goodwin, G. W., Taylor, C. S., Taegtmeyer, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+energy+metabolism+of+the+heart+during+acute+increase+in+heart+work.">Regulation of energy metabolism of the heart during acute increase in heart work.</a> J Biol Chem. 273, 29530-29539 (1998).</li><li>Lopaschuk, G. D., Ussher, J. R., Folmes, C. D., Jaswal, J. S., Stanley, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Myocardial+fatty+acid+metabolism+in+health+and+disease.">Myocardial fatty acid metabolism in health and disease.</a> Physiol Rev. 90, 207-258 (2010).</li><li>Neely, J. R., Denton, R. M., England, P. J., Randle, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effects+of+increased+heart+work+on+the+tricarboxylate+cycle+and+its+interactions+with+glycolysis+in+the+perfused+rat+heart.">The effects of increased heart work on the tricarboxylate cycle and its interactions with glycolysis in the perfused rat heart.</a> Biochem J. 128, 147-159 (1972).</li><li>Katz, J., Dunn, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose-2-t+as+a+tracer+for+glucose+metabolism.">Glucose-2-t as a tracer for glucose metabolism.</a> Biochemistry. 6, 1-5 (1967).</li><li>Gillis, A. M., Kulisz, E., Mathison, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cardiac+electrophysiological+variables+in+blood-perfused+and+buffer-perfused,+isolated,+working+rabbit+heart.">Cardiac electrophysiological variables in blood-perfused and buffer-perfused, isolated, working rabbit heart.</a> Am J Physiol. 271, H784-H789 (1996).</li><li>Qiu, Y., Hearse, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+ischemic+vulnerability+and+responsiveness+to+cardioplegic+protection+in+crystalloid-perfused+versus+blood-perfused+hearts.">Comparison of ischemic vulnerability and responsiveness to cardioplegic protection in crystalloid-perfused versus blood-perfused hearts.</a> J Thorac Cardiovasc Surg. 103, 960-968 (1992).</li><li>Cotter, D. G., Schugar, R. C., Crawford, P. 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J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+rates+of+protein+in+the+Langendorff-perfused+rat+heart+in+the+presence+and+absence+of+insulin,+and+in+the+working+heart.">Synthesis rates of protein in the Langendorff-perfused rat heart in the presence and absence of insulin, and in the working heart.</a> Biochem J. 132, 603-608 (1973).</li><li>Hindlycke, M., Jansson, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose+tolerance+and+pancreatic+islet+blood+flow+in+rats+after+intraperitoneal+administration+of+different+anesthetic+drugs.">Glucose tolerance and pancreatic islet blood flow in rats after intraperitoneal administration of different anesthetic drugs.</a> Ups J Med Sci. 97, 27-35 (1992).</li><li>Zuurbier, C. J., Keijzers, P. J., Koeman, A., Van Wezel, H. B., Hollmann, M. 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D., Larsen, T. S., Lopaschuk, G. D., Severson, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose+and+fatty+acid+metabolism+in+the+isolated+working+mouse+heart.">Glucose and fatty acid metabolism in the isolated working mouse heart.</a> Am J Physiol. 277, R1210-R1217 (1999).</li><li>Iannaccone, P. M., Jacob, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rats!+.">Rats! .</a> Dis Model Mech. 2, 206-210 (2009).</li></ol>

The preceding protocol details the methods to simultaneously quantify the flux of substrate through glucose oxidation and fatty acid oxidation in the isolated working rat heart. The measurements can then be superimposed to the recorded cardiac functional parameters to determine the relationship between substrates metabolism and cardiac work under baseline and stress conditions (change in workload, ischemia-reperfusion, etc&#8230;). It is also possible to evaluate how the metabolism/contraction relationship is af...

Clinical Relevance
In the mammalian heart, there is a strong positive relationship between the flux of substrates through oxidative metabolic pathways, ATP generation and cardiac work1. Over the past two decades, the investigation of the intricate link between cardiac metabolism and function has led to recognize that alterations in cardiac metabolism are a cause for contractile dysfunction and possibly pathological structural remodeling in the setting of different types of heart disease2-4.Therefore, it is expected that our understanding of the mechanisms governing metabolic remodeling of the stressed heart will lead to the identification of therapeutic targets for the prevention or treatment of heart failure5-7. The recent publication of a scientific statement from the American Heart Association on &#34;Assessing Cardiac Metabolism&#34; emphasizes the growing interest of the scientific community for this field of research8. But while the technological advances in cardiac imaging now allow for a rapid and accurate evaluation of cardiac morphology and function, the in vivo study of cardiac metabolism remains limited and burdensome: Nuclear Magnetic Resonance (NMR) spectroscopy and Positron Emission Tomography (PET) imaging can be used to follow cardiac high energy phosphate metabolism and Krebs cycle activity, but these techniques are plagued by high operating costs and by their inability to determine the contribution of various substrates to oxidative metabolism in steady-state conditions9.To this date the ex vivo working heart preparation represents the sole and unique technique available to study, simultaneously and in real time, contractile function and flux of substrates into oxidative metabolic pathways7,9. The following protocol aims to provide guidelines in the preparation and utilization of reagents used to determine the rates of substrates utilization in the isolated working rat heart.
The Isolated Working Rodent Heart Apparatus
Although the technique is almost half a century old, the isolated working rat heart preparation remains a method of choice for cardiovascular research. As with the Langendorff heart preparation, the working rodent heart offers a relatively simple, reliable, and inexpensive way to measure a wide range of cardiac parameters independently from the confounding effects of other organs, neurohormonal and other circulating factors. But in contrast to the Langendorff-perfused heart, the working heart continues to perform near-physiological cardiac work, a prerequisite for the generation of oxidative metabolic flux to levels that are relevant to in vivo conditions. This is achieved by delivering the perfusion buffer to the left ventricle (LV) via a cannula connected to the left atrium, and as the LV fills and contracts, the buffer is ejected through the aortic line against a determined afterload hydrostatic pressure. The design of the perfusion apparatus originally described by Neely and colleagues10 was subsequently improved by Taegtmeyer, Hems and Krebs11, but has changed very little ever since. As described in the original apparatus, contractile function can be assessed through determination of cardiac output, using no more than graduated cylinders and a stopwatch to measure aortic and coronary flows10,11. Several vendors now offer complete working rodent heart perfusion systems. These commercially available apparatus can be acquired with flowprobes, pressure transducers, a pressure-volume catheter and all the equipment necessary for cardiac functional data acquisition and analysis. The vendors provide extensive documentation and training sessions to familiarize the new user with their equipment. Several review articles also detail protocols on the working heart instrumentation and on the use of catheters to measure cardiac function in rodents12-15. For this reason, we will only briefly mention the set-up of the perfusion apparatus and the recording equipment. The present protocol rather aims to complement the already available information with a description of the methods that can be implemented to simultaneously measure the rates of glucose and long-chain fatty acid oxidation, the two major energy providing substrates in the normal heart. We describe here all the steps involved in the use of radiolabeled energy substrates for the assessment of myocardial oxidative metabolism, from the preparation of reagents and buffers to the recovery and processing of samples, to the data analysis.
Principles of the Method
Cardiomyocytes generate the bulk of their energy for contraction from the oxidative phosphorylation of fatty acids (principally long-chain fatty acids) and carbohydrates (glucose and lactate). The heart has very limited energetic reserves and relies on a constant supply of these energy providing substrates from the circulation. The catabolism of glucose through the glycolytic pathway yields pyruvate which is then decarboxylated by the pyruvate dehydrogenase complex of the inner mitochondrial membrane. Long-chain fatty acids, extracted from circulating albumin or lipoprotein triglycerides, are first activated into acyl-CoA molecules in the cytosol and subsequently transported inside the mitochondrial matrix through the carnitine shuttle to enter the beta-oxidation pathway. The acetyl-CoA molecules produced by the catabolism of glucose and fatty acids fuel the Krebs cycle to generate the reducing equivalents (NADH and FADH2) which are used by the electron transport chain to build the proton-motive force across the inner mitochondrial membrane and generate ATP through the activity of the ATP synthase. Water and carbon dioxide are the end byproducts of the enzymatic reactions taking place inside the Krebs cycle. The supply of 14C- and 3H- radiolabeled substrates (such as 14C-radiolabeled glucose and 3H-radiolabeled oleic acid) to the isolated working heart will consequently lead to the production of 14CO2 and 3H2O which can be quantitatively recovered from the coronary effluent. The collection of 14CO2 is carried out by keeping the isolated perfused heart into a sealed chamber and by immediately recovering the coronary effluent as it exits the heart. A small anion exchange column is used to separate and recover 3H2O from the coronary effluent. The radioactivity from the processed samples is measured with a liquid scintillation counter, and with knowledge of the specific activity of the radiolabeled substrates used, it is then possible to individually quantitate the flux of glucose and fatty acid in the oxidation pathways16,17.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Sodium Chloride (NaCl)</td>
			<td>Fisher Scientific</td>
			<td>BP358</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Chloride (KCl)</td>
			<td>Fisher Scientific</td>
			<td>BP366</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Phosphate Monobasic (KH2PO4)</td>
			<td>Fisher Scientific</td>
			<td>P284</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Sulfate Heptahydrate (MgSO4*7H2O)</td>
			<td>Fisher Scientific</td>
			<td>M63</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Bicarbonate (NaHCO3)</td>
			<td>Fisher Scientific</td>
			<td>S233</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride (CaCl2)</td>
			<td>Sigma-Aldrich</td>
			<td>C5670</td>
			<td></td>
		</tr>
		<tr>
			<td>AG 1-X8 resin, chloride form, 100-200 dry mesh size, 500 g</td>
			<td>Bio-Rad</td>
			<td>1401441</td>
			<td>This item can be replaced by purchasing directly the hydoxide form&#160; (see reference below), but this will cost almost 8 times more</td>
		</tr>
		<tr>
			<td>AG 1-X8 resin, hydroxide form, 100-200 dry mesh size, 100 g</td>
			<td>Bio-Rad</td>
			<td>1432445</td>
			<td>Purchasing this item allows to bypass the conversion of the anion exchange resin from the chloride form to the hydroxide form (See section 1.2 of protocol)</td>
		</tr>
		<tr>
			<td>Glass Microanalysis Vacuum Filter Holder</td>
			<td>Fisher Scientific</td>
			<td>09-753-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Hydroxide (NaOH)</td>
			<td>Fisher Scientific</td>
			<td>S318</td>
			<td>Corrosive. Consult the product MSDS for appropriate handling and storage.</td>
		</tr>
		<tr>
			<td>Gas Dispersion Tube with Fritted Cylinder</td>
			<td>Fisher Scientific</td>
			<td>11-138B</td>
			<td></td>
		</tr>
		<tr>
			<td>Probumin Bovine Serum Albumin Fatty Acid Free, Powder</td>
			<td>EMD Millipore</td>
			<td>820027</td>
			<td>We recommend the use of a charcoal-defatted BSA, as other purification process such as cold ethanol fractionation may leave residues toxic for the heart.</td>
		</tr>
		<tr>
			<td>Sodium Oleate</td>
			<td>Sigma-Aldrich</td>
			<td>O7501</td>
			<td></td>
		</tr>
		<tr>
			<td>Oleic Acid, [9,10-3H(N)]-</td>
			<td>PerkinElmer</td>
			<td>NET289005MC</td>
			<td>Radioactive material. Follow your Institution&#39;s radiation safety office guidelines for ordering and handling.</td>
		</tr>
		<tr>
			<td>Dialysis Membrane Tubing, 29 mm diameter</td>
			<td>Fisher Scientific</td>
			<td>08-667E</td>
			<td></td>
		</tr>
		<tr>
			<td>D-(+)-Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G7021</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose, D-[14C(U)]-</td>
			<td>PerkinElmer</td>
			<td>NEC042B005MC</td>
			<td>Radioactive material. Follow your Institution&#39;s radiation safety office guidelines for ordering and handling.</td>
		</tr>
		<tr>
			<td>Humulin R U-100</td>
			<td>Eli Lilly and Company</td>
			<td>NDC 0002-8215-01 (HI-210)</td>
			<td></td>
		</tr>
		<tr>
			<td>Inactin Hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>T133</td>
			<td>Controlled substance on USDEA Schedule III</td>
		</tr>
		<tr>
			<td>3-0 Silk Black Braid</td>
			<td>Roboz Surgical</td>
			<td>SUT-15-3</td>
			<td></td>
		</tr>
		<tr>
			<td>10X Hyamine Hydroxide</td>
			<td>PerkinElmer</td>
			<td>6003005</td>
			<td>Highly toxic and causes severe burns. Consult the product MSDS for appropriate handling and storage</td>
		</tr>
		<tr>
			<td>20 mL Glass Scintillation Vials</td>
			<td>Fisher Scientific</td>
			<td>03-341-25E</td>
			<td>Use glass vials for quantitative recovery of 14CO2</td>
		</tr>
		<tr>
			<td>20 mL HDPE Scintillation Vials</td>
			<td>Fisher Scientific</td>
			<td>03-337-23B</td>
			<td>Use HDPE vials for quantitative recovery of 3H2O</td>
		</tr>
		<tr>
			<td>Red Rubber Sleeve Stoppers</td>
			<td>Fisher Scientific</td>
			<td>14-126DD</td>
			<td>Fit 20 mL scintillation vials; Reusable</td>
		</tr>
		<tr>
			<td>BD PrecisionGlide Needle 23G x 40 mm</td>
			<td>BD</td>
			<td>305194</td>
			<td>Use to inject perchloric acid through the rubber sleeve stopper of the CO2 trap</td>
		</tr>
		<tr>
			<td>Perchloric Acid, 60%</td>
			<td>Fisher Scientific</td>
			<td>A228</td>
			<td>Highly corrosive and may act as an oxidizer and/or cause an explosion hazard. Consult the product MSDS for appropriate handling and storage</td>
		</tr>
		<tr>
			<td>Ultima Gold, Scintillation Cocktail</td>
			<td>PerkinElmer</td>
			<td>6013327</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass Wool</td>
			<td>Fisher Scientific</td>
			<td>AC38606</td>
			<td></td>
		</tr>
		<tr>
			<td>Decon Dri-Clean Detergent Powder</td>
			<td>Fisher Scientific</td>
			<td>04-355</td>
			<td>For cleaning of glassware, plastic parts, and tubing</td>
		</tr>
		<tr>
			<td>Alconox Tergazyme Enzyme-Active Powered Detergent</td>
			<td>Fisher Scientific</td>
			<td>16-000-115</td>
			<td>For cleaning of &#34;hard to reach&#34; surfaces (tubing, glassware) contaminated by fatty acid-BSA residue</td>
		</tr>
	</tbody>
</table>

methods for the determination of rates of glucose and fatty acid oxidation in the isolated working rat heart

The mammalian heart is a major consumer of ATP and requires a constant supply of energy substrates for contraction. Not surprisingly, alterations of myocardial metabolism have been linked to the development of contractile dysfunction and heart failure. Therefore, unraveling the link between metabolism and contraction should shed light on some of the mechanisms governing cardiac adaptation or maladaptation in disease states. The isolated working rat heart preparation can be used to follow, simultaneously and in real time, cardiac contractile function and flux of energy providing substrates into oxidative metabolic pathways. The present protocol aims to provide a detailed description of the methods used in the preparation and utilization of buffers for the quantitative measurement of the rates of oxidation for glucose and fatty acids, the main energy providing substrates of the heart. The methods used for sample analysis and data interpretation are also discussed. In brief, the technique is based on the supply of 14C- radiolabeled glucose and a 3H- radiolabeled long-chain fatty acid to an ex vivo beating heart via normothermic crystalloid perfusion. 14CO2 and 3H2O, end byproducts of the enzymatic reactions involved in the utilization of these energy providing substrates, are then quantitatively recovered from the coronary effluent. With knowledge of the specific activity of the radiolabeled substrates used, it is then possible to individually quantitate the flux of glucose and fatty acid in the oxidation pathways. Contractile function of the isolated heart can be determined in parallel with the appropriate recording equipment and directly correlated to metabolic flux values. The technique is extremely useful to study the metabolism/contraction relationship in response to various stress conditions such as alterations in pre and after load and ischemia, a drug or a circulating factor, or following the alteration in the expression of a gene product.

Two representative experiments are described in the figures below. In both cases, the heart of a 16 week old male Sprague Dawley rat was isolated and perfused in the working mode with KH buffer prepared according to the preceding protocol. In each experiment, the heart was subjected to a stress condition to affect cardiac work. Cardiac contractile function was assessed by continuous recording of pulse pressure through insertion of a pressure transducer in the aortic line and by determinat...

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Methods for the Determination of Rates of Glucose and Fatty Acid Oxidation in the Isolated Working Rat Heart

The following protocol describes the preparation and utilization of buffers for the quantitative measurement of rates of glucose and fatty acid oxidation in the isolated working rat heart. The methods used for sample analysis and data interpretation are also discussed.

The mammalian heart is a major consumer of ATP and requires a constant supply of energy substrates for contraction. Not surprisingly, alterations of ...

The overall goal of this procedure is to obtain simultaneous real time measures of myocardial rates of glucose oxidation and fatty acid oxidation, as well as cardiac contractual function in an isolated working rat heart. This method can help answer key questions in the cardiovascular field. Such as how the heart metabolically adapts to acute changes in energy demands and how these responses affected in pathological conditions.The main advantage of this technique is that it provides the investigator total control over the environmental variables such as the nature and the concentrations of substrates, drugs, or hormones delivered to the heart. The most would be Bhavisha Bakrania a post doctoral fellow from the cardiovascular Reno resource center at the University of Mississippi Medical Center. To begin, start the pump to prime the perfusion apparatus and to oxygenate the buffer.After preparing the materials, anesthetize a rat and prepare it for surgery. Clip the abdomen free of hair and perform a mid line incision with lateral extension. Move the stomach and intestine aside to access the inferior vena cava and inject 200 USP units of Heparin.Wait five to 10 seconds, then using scissors cut the diaphragm and the sides of the rib cage to expose the contents of the chest cavity. Next, delicately grab the heart using the hand and excise both the heart and lungs together. Cut at the level of the descending aorta, being careful not to damage the aortic arch and ascending aorta in the process.Immediately transfer the heart and lungs to a dissection dish filled with ice cold KH buffer. After the heart stops beating, learn to work quickly so it can be restarted within a minute or two. Now submerge the heart and lungs in a new dish of ice cold KH buffer.Quickly trim off any large pieces of lung tissue, then cut the descending aorta right above the aortic arch. For the following steps, take the necessary precautions for use of radioactives. Next, using forceps carefully open the aorta and slide the heart up onto the cannula.Be very careful not pass the aortic route with a cannula, as this may cause hypoperfusion of the heart and damage to the aortic valves. Now, secure the junction with a micro clip and initiate the Lagendorff perfusion of the heart. Without rushing, secure the aorta to the aortic cannula using a 3 0 silk suture and remove the micro clip.Then locate the pulmonary vein and trim away non cardiac tissues as needed. Leave enough tissue to anchor the left atrium to the cannula. The cannulation of the left atrium is the second most critical step of the protocol as improper insertion of the cannula or the presence of a leak will weaken contractions and compromise the quantification of metabolic rates.Next, prepare the left atrial line cannula, just as done for the right cannula. Then with forceps, delicately grab the opening of the pulmonary vein and slide the heart up on the atrial cannula. Move the tissues as needed without bending the aorta or overly straining the heart.Then secure the cannula with a 3 0 silk suture. Finally, open the atrial line while simultaneously switching the aortic line to working mode. If buffer leaks out from the left atrium, close the atrial line and switch back to Lagendorff mode.Then use more sutures to better secure the cannula and try switching to working mode again. If the experiment includes direct measurement of LV function with a catheter, then begin by puncturing the LV apex using a 26 gauge needle, introduce a pressure volume catheter and align the shaft with the LV longitudinal axis. Then position the distal electrode E1 just below the aortic valve, adjacent to the endocardial border and position the proximal electrode E4 just inside the ventricular wall.Now seal the heart in a water jacketed chamber. Then start monitoring functional parameters in the software. Once baseline parameters have been stable for at least five minutes, start recording data.To measure the coronary flow, record the time it takes to collect 20 milliliters of effluent. Then take two millimeters of the effluent into a syringe via the three way stopcock and discard the remainder. Immediately transfer the two milliliter sample into a micro centrifuge tube and take a half milliliter aliqout to determine the rate of glucose oxidation.Store the rest on ice. Continue taking coronary effluence samples periodically and before finishing, inject 10 micro liters of hypertonic saline into the atrial line. Just before it attaches to the cannula.Use the response to this bolus to calculate the parallel conductance for accurate determination of cardiac volume. Next, unseal the heart chamber and remove the catheter in the LV.Then cut the heart off the cannulas and drop it into ice cold KH buffer. Now, quickly dry the heart on a paper towel and measure its wet weight.Once weighed, proceed to dissect the required tissue samples and then freeze the remaining tissue using tongs cooled on dry ice. In preparation, load glass scintillation vials with one milliliter of 10x hyamine hydroxide. Prepare one for each coronary effluence sample and two for controls.As soon as a sample vial is loaded, place it directly into a loaded scintillation vial. For the analysis, delicately cap the vial with a rubber sleeve stopper and use parafilm to seal the vial. Now, using a one milliliter syringe with a long 23 gauge needle, inject 200 micro liters of 60%perchloric acid through the rubber sleeve.Let all the sample vials sit overnight. The next day, carefully retrieve each sample tube with tweezers and wash their bottoms off over the open vials with one milliliter of scintillation cocktail to retrieve all of the hydroxide of hyamine. Then add nine more milliliters of scintillation cocktail to each vial.To get the specific activity, add 0.5 milliliters of profusion buffer into two of the vials. Now shake the vials vigorously and let the vial settle for at least six hours before taking measurements. To determine the myocardial oleate oxidation rates, first prepare an anionic exchange resin column for each sample.Just load the tips of three milliliters syringe tubes with glass wool. Then add the resin water slurry up to the two milliliter mark in each column using a transfer pipette. Next, wash the resin by passing two milliliters of ultra pure water through each column three times.Then place scintillation vials under the columns and load the columns with a half milliliter of coronary effluent. For the background measurement, use perfusion buffer instead. Now, elute the columns successively with one half milliliter, one milliliter, and finally two milliliters of ultra pure water.Discard the columns. Then add 13 milliliters of scintillation cocktail to the vials. Add 0.5 milliliters of perfusion buffer directly to two vials filled with 13 milliliters of liquid scintillation cocktail for determination of the specific activity.Vigorously shake the vials, let them settle for six plus hours and take measurements. Hearts were isolated from two 16 week rats and subjected to different stress conditions. For one heart, an acute increase in work load was simulated by increasing the after load by 40%and by adding epinephrine to the perfusion buffer.The heart rate immediately increased by more than 50%with the work jump induction. The cardiac power increased by more than 40%at the work jump, which was accompanied by an increase in both rates of glucose and oleate oxidation. The relative increase from base line for glucose oxidation was striking.The other heart was subjected to 15 minutes of global ischemia and 30 minutes of reperfusion. Under these experimental conditions, a near normal pulse pressure was restored a few minutes into the reperfusion. Within 10 minutes, cardiac power rapidly increased to above pre-ischemia values before returning to near baseline values.This resulted from increased oleate oxidation. Where as glucose oxidation was quick to resume to pre-ischemic activity. Once mastered, isolation of the heart to the initial reperfusion in the working mode can be done in less than five minutes if performed properly.Following this procedure, other methods such as RNA and protein expression analyses can be done in order to answer additional questions, such as the effect of a drug or stress condition on molecular signaling pathways. Don't forget that working with radio tracers can be extremely hazardous and precautions such as wearing full personal protective equipments should be always taken while performing this procedure.

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14.5K vistas.  University of Mississippi Medical Center. The overall goal of this procedure is to obtain simultaneous real time measures of myocardial rates of glucose oxidation and fatty acid oxidation, as well as cardiac contractual function in an isolated working rat heart. This method can help answer key questions in the cardiovascular field. Such as how the heart metabolically adapts to acute changes in energy demands and how these responses affected in pathological conditions.The main advantage of this technique is that it provides the...