The chronic administration of isoproterenol via an osmotic pump has been widely used to recapitulate changes in advanced heart failure in mice. This method is simple and requires less surgical expertise than other models, such as LAD and TAC. Demonstrating the procedure will be Dr.Vincent Ren, a research scientist from Dr.Yibin Wang's laboratory.
After weighing and recording the body weight of each mouse, calculate the appropriate amount and concentration of isoproterenol for each animal, and dissolve the isoproterenol in 120 microliters of sterile 0.9%sodium chloride. Mix thoroughly for one minute to completely solubilize the isoproterenol, and weigh and record the weight of one empty osmotic pump, together with and without its flow moderator, per mouse. Attach a 27-gauge, blunt-tipped filling tube provided with the osmotic pumps, and load one, one-milliliter syringe with 120 microliters of the isoproterenol solution per mouse.
Holding a pump in the upright position, insert the filling tube through the pump opening at the top until the tip of the filling tube sits near the bottom of the pump reservoir, and slowly depress the syringe plunger until the isoproterenol solution fills to the pump opening. When the pump has been loaded, carefully remove the filling tube, and wipe off the excess solution. Insert back the flow moderator to close the pump, and wipe off any excess solution.
Then reweigh the pump to confirm that over 90%of the reservoir volume has been filled. Place the mouse in the supine position on a heated pad, and remove the air from the lower abdomen. For surgical osmotic pump implantation, confirm a lack of response to toe pinch in an anesthetized mouse, and apply ointment to the animal's eyes.
Clean the exposed skin with a suitable disinfectant, and make a one-centimeter midline skin incision. Use a pair of blunt-ended scissors to carefully dissect the skin from the underlying peritoneal walls, and use forceps to pull the peritoneal walls away from the underlying bowel. Use fine scissors to cut a 0.8-centimeter hole in the peritoneal wall, and insert the osmotic pump flow moderator end first into the peritoneal cavity.
When the pump is in place, use 5-0 absorbable sutures in an interrupted fashion to close the hole in the peritoneal wall, and use 6-0 nonabsorbable sutures to close the skin. Then place the mouse in a dedicated incubator with monitoring until full recumbency before returning the animal to its home cage. Here, a summary of the weekly changes based on the selected echocardiographic parameters and the expected time to model development are presented.
Although variations are observed between mouse strains, on average, interventricular septal wall thickness at end diastole and fractional shortening increase in the first week but decrease by later time points. The left ventricular internal diameter at end diastole and the left ventricular mass increase over a period of three weeks. Further, mouse hearts demonstrate visibly larger left ventricular chamber dimensions under isoproterenol, as well as greater amounts of fibrosis relative to saline-treated controls.
It is critical to maintain a sterile surgical environment during the survival surgery to minimize post-operative infection and morbidity. Successful model creation can be assessed in vivo by serial echocardiography for hypertrophy, dilation, and dysfunction, as well as ex vivo via histological and molecular assessment of harvested cardiac tissue. We have applied this method to over 100 strains of inbred mice to assess cardiac remodeling traits due to chronic beta-adrenergic stimulation.
The results are published and readily available.
