ADRENERGIC BETA RECEPTORS AND PLASMA FREE FATTY ACIDS

¹ Departments of Biology and Biochemistry, Ayerst Research Laboratories, Montreal, Quebec, Canada

The importance of the sympathetic nervous system in the generation of free fatty acids (FFA) is well recognized. The question arises about which type of adrenergic receptor is involved in this mechanism. In the present study, the effect of four adrenergic beta receptor blocking agents on plasma FFA, serum glucose, heart rate, blood pressure and electrocardiogram was examined in anesthetized dogs and cats. Given intravenously to dogs, pronethalol and dichloroisoprotenerol consistently produced a prolonged and pronounced elevation of plasma FFA, while no such change was observed after propranolol or MJ-1999. Similar results were obtained in cats. Propranolol, although not affecting the plasma FFA level per se, like pronethalol, still suppressed the FFA increase induced by epinephrine or isoproterenol, and diminished that caused by amphetamine. In contrast, the adrenergic alpha receptor blocking agent dibenamine did not have these properties. It is postulated that the adrenergic receptors involved in the generation of FFA are similar to, but not identical with, the adrenergic beta receptors in the cardiovascular system. No correlation was detected between the effect of beta receptor blocking agents on plasma FFA and serum glucose concentrations.