Cardiac function in rats selectively bred for low- and high-capacity running

Rat genetic models of intrinsic (i.e., untrained) low-capacity runners (LCR ) and high-capacity runners (HCR) are being developed by artificial selecti ve breeding for treadmill running. At generation 3, these lines differed in running capacity by 114%. We used generation 3 rats to test the hypotheses that HCR, relative to LCR, have 1) greater isolated cardiac performance an d 2) more resistance to myocardial ischemic insult. The LCR ran for 227 +/- 7 m, and the HCR ran 994 +/- 11 m at exhaustion (337% difference, P < 0.00 1). Isolated heart performance was assessed from cardiac output (CO) genera ted at constant preload (15 mmHg) and afterload (70 mmHg) using a Langendor ff-Neely working heart preparation. CO averaged 33.5 +/- 2.0 ml.min(-1).g(- 1) in LCR hearts and 49.9 +/- 1.4 ml.min(-1).g(-1) in HCR hearts (49% diffe rence, P < 0.001). Recovery of CO after 25 min of global ischemia was not d ifferent between the lines. These results suggest that 1) increased cardiac performance accounts for part of the difference in running capacity betwee n the lines; and 2) unlike exercise training, genetically determined intrin sic capacity for exercise does not influence the recovery from 25 min of gl obal low-flow cardiac ischemia.