EFFECTS OF HYPOTHERMIA ON ENERGY-METABOLISM IN RAT AND RICHARDSONS GROUND-SQUIRREL HEARTS

Glycolysis, glucose oxidation, palmitate oxidation, and cardiac functi on were measured in isolated working hearts from ground squirrels and rats subjected to a hypothermia-rewarming protocol. Hearts were perfus ed initially for 30 min at 37 degrees C, followed by 2 h of hypothermi c perfusion at 15 degrees C, after which hearts were rewarmed to 37 de grees C and further perfused for 30 min. Functional recovery in ground squirrel hearts was greater than in rat hearts after rewarming. Hypot hermia-rewarming had a similar general effect on the various metabolic pathways in both species. Despite these similarities, total energy su bstrate metabolic rates were greater in rat than ground squirrel heart s during hypothermia despite a lower level of work being performed by the rat hearts, indicating that rat hearts are less efficient than gro und squirrel hearts during hypothermia. After rewarming, energy substr ate metabolism recovered completely in both species, although cardiac work remained depressed in rat hearts. The difference in functional re covery between rat and ground squirrel hearts after rewarming cannot b e explained by general differences in energy substrate metabolism duri ng hypothermia or after rewarming.