LIPID-ACCUMULATION IN ISOLATED-PERFUSED RAT HEARTS HAS NO APPARENT EFFECT ON MECHANICAL FUNCTION OR ENERGY-METABOLISM AS MEASURED BY P-31 NMR

Male Sprague-Dawley rats were fed diets that contained 20% by weight s oybean oil or rapeseed oil (21% and 43% erucic acid) for 7 days. The r apeseed oil diets increased the cardiac triacylglycerol content 5-fold and 25-fold, respectively, above control values. Hearts were removed from the animals and perfused with modified Krebs-Henseleit buffer at 37-degrees-C. The calculated rate-pressure product was used as a measu re of contractile function. P-31 NMR spectra were acquired throughout a protocol that consisted of 12 min control perfusion, followed by 12 min perfusion with 20 mum isoproterenol, 12 min washout, 12 min total global ischemia, and 28 min reperfusion. The steady state levels of cr eatine phosphate, ATP, intracellular pH, contractile function, and the free energy of ATP hydrolysis (DELTAG(ATP)) were determined for all t hree groups of hearts. Isoproterenol more than doubled the rate-pressu re product of the hearts on all diets and decreased the concentrations of creatine phosphate and ATP with a concomitant rise in Pi. After gl obal ischemia, creatine phosphate levels recovered fully, ATP levels r emained low, and most hearts developed ventricular fibrillation. Chang es in intracellular pH were the same for all groups: pH was 7.1 throug hout the equilibration and isoproterenol perfusion period, decreased t o pH approximately 6.4 during ischemia, and returned to 7.0 during rep erfusion. The results indicate that the fat accumulation that occurs i n the hearts of rats fed diets rich in high erucic acid rapeseed oil d oes not interfere with the cardiac high energy phosphate metabolism or contractile function. These data imply that the free fatty acid in th ese hearts did not reach the levels required to uncouple oxidative pho sphorylation.