Effect of isoproterenol on the metabolism of myocardial fatty acids

The effect of β -adrenergic stimulation on myocardial fatty acid metabolism was studied in the anesthetized open-chest dog. Isoproterenol (1 μg/kg/min) was infused; and samples of arterial blood and of left ventricular wall were taken at the 5th min for the determination of the following variables: (1) in arterial blood: lactate and serial free fatty acids (FFA); (2) in myocardial tissue: creatine phosphate (CP), ATP, lactate, carnitine, acylcarnitine, glycerol, and the fatty acid content of each of phospholipids (PL), cholesterol esters (CE), triglycerides (TG), diglycerides (DG), monoglycerides (MG), and FFA. A capillary gas chromatography was used for fatty acid assay. Isoproterenol decreased the content of creatine phosphate but not of ATP. Lactate increased in both arterial blood and myocardial tissue. The five-fold increase in arterial FFA ( P β -stimulation in comparison with control group (2694±689 vs. 7518±833 nmol/g wet wt, P P The most marked individual changes (except in PL) were observed on monounsaturated fatty acids, 18: 1 ω 9, 18: 1 ω 7, and 16:1 cis . The significant changes of monounsaturated/saturated and of 16:1 cis /16: 1 trans ratios, in arterial FFA and tissue TG, suggested modifications in the distribution of fatty acids. Polyunsaturated, 18:2 and 18:3 ω 3, were less modified than monounsaturated; and C 20 fatty acid changes were negligible. It may be concluded that: (1) β -stimulation leads to a mobilization of heart lipids, and primarily to the mobilization of triglyceride; (2) Acylcarnitine formation is enhanced; (3) The unsaturated fatty acids, and particularly the monounsaturated, are mobilized in preference to saturated; and the metabolism of cis -isomers is faster than that of trans -isomers.