Adrenergic effects on plasma levels of glucagon, insulin, glucose and free fatty acids in rabbits--influences of selective blocking drugs.

Abstract

Species differences concerning the effects of alpha- and beta-receptor stimulation on glucagon release and carbohydrate metabolism have been reported. The aim of the present study was to investigate how the subtypes of alpha- and beta-receptors regulate the plasma levels of glucagon, insulin, glucose and free fatty acids in fasted rabbits. Epinephrine-induced 1) hyperglucagonaemia, 2) hypoinsulinaemia and 3) hyperglycaemia were significantly inhibited by alpha-2 receptor blockade (yohimbine), and not influenced by alpha-1 receptor blockade (prazosin). Isoproterenol-induced 1) hyperglucagonaemia was not affected by beta-1 or beta-2 receptor blockade, 2) hyperinsulinaemia was inhibited by a lower dose of beta-2 (ICI 118.551) than beta-1 receptor blockade (metoprolol), 3) hyperglycaemia was inhibited by beta-2 receptor blockade and 4) increases in the plasma levels of free fatty acids were blocked by beta-1 receptor blockade. It is concluded that in fasted rabbits: 1) plasma levels of glucagon are mainly increased by alpha-2 receptor stimulation, 2) plasma levels of insulin are decreased by alpha-2 receptor stimulation, and increased more by beta-2 than by beta-1 receptor stimulation, 3) plasma levels of glucose are increased by alpha-2 and beta-2 receptor stimulation and 4) the plasma levels of free fatty acids are increased by beta-1 receptor stimulation.