Fatty acid oxidation by isolated perfused working hearts of aged rats.

It has been reported that mitochondria isolated from hearts of old rats have lower respiratory activity than mitochondria from young rats. In order to determine the physiological correlates of these changes, the metabolism of hearts from young and old rats has been compared in a perfused working heart preparation. The oxidation of [14C]palmitate to 14CO2, oxygen consumption, and nucleotide levels were measured under different cardiac workloads. The hearts from old animals performed less cardiac work and utilized less oxygen and palmitate in proportion to tissue mass, but the ratio of oxygen consumed to pressure developed was unaltered. There was a small but significant decrease in cardiac efficiency expressed as the ratio between the rate of oxygen consumed and ventricular pressure development. Tissue levels of total carnitine and long-chain acylcarnitine derivatives were greatly reduced in the older heart without significant change in free CoA, acetyl-CoA, or long-chain acyl-CoA. The adenine nucleotide levels were not significantly different in the two groups. The results appear consistent with the in vitro studies on isolated mitochondria.