Coronary autoregulation and metabolism in hypothermic rat and ground squirrel hearts

An isovolumic Langendorff preparation was used to perfuse rat and ground squirrel (Spermophilus tridecemlineatus) hearts at 37, 27, 17, and 7 degrees C. Perfusion pressure (PP) was randomly increased or decreased (40, 60, 70, 110, 120, or 140 mmHg) from a control PP of 90 mmHg. Coronary flow (CF) was measured immediately after each PP change (initial CF) and after stable flow was observed (final CF). Compared with initial flow, final CF was decreased at high PPs or increased at low PPs (autoregulation) in hearts from both species, but rat hearts did not autoregulate CF or develop left ventricular systolic pressure (LVSP) at 7 degrees C. Squirrel hearts generated LVSP at all temperatures and perfusion pressures. LVSP and initial CF were proportional to PP in both species, but squirrel heart LVSP was independent of PP at 7 degrees C. Myocardial O2 consumption (MVO2) was highly correlated with CF in all hearts at 37 degrees C but not at lower temperatures. Squirrel hearts were more efficient (MVO2 vs. HR X LVSP) than rat hearts at low temperatures but less efficient at 37 degrees C. The intrinsic temperature adaptations displayed by squirrel hearts would support continued myocardial function when body temperature and blood pressure fluctuate throughout the stages of hibernation.