[Intermediate myocardial metabolism. Changes in ischemia, diabetes and hyperthyroidism].

Long-chain free fatty acids (FFA) are oxidized, in preference to carbohydrates, by a myocardium with normal oxygen supply. Their utilization is increased in diabetes and most probably also in hyperthyroidism, since in both cases plasma FFA concentrations are augmented. Under conditions of ischaemia, the long-chain fatty acid esters of coenzyme A (CoA) and carnitine accumulate in cells. This accumulation depends on the degree of coronary blood flow reduction, being very high in moderate ischaemia and much reduced when the coronary flow is nul. The accumulation of acyl-CoA and acylcarnitine in ischaemic myocardium is amplified by diabetes. The presence in the cells of these amphophilic compounds (notably acylcarnitine) in high concentrations has been associated with changes in the structure and properties of mitochondrial and sarcolemmal membranes. Finally, the accumulation of glycolysis end-products (e.g. lactates and protons) may condition the degree of functional recovery from global and total ischaemia. In this respect, recently obtained in vitro data show that a decrease in cellular pH may be one of the determinant factors in reperfusion.