AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 2 357-R365, Copyright © 1989 by American Physiological Society
Coronary autoregulation and metabolism in hypothermic rat and ground squirrel hearts
R. F. Burlington, M. S. Dean and S. B. Jones
Department of Biology, Central Michigan University, Mt. Pleasant 48859.
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.
