Effect of some β-adrenoceptor blocking drugs on insulin secretion in the rat

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Abstract
In pentobarbitone anaesthetized rats (±)-propranolol reduced the stimulatory effect of glucose, sulphonylureas, isoprenaline or phentolamine on insulin secretion. (+)-Propranolol produced similar effects to those produced by the racemate. Sotalol reduced only the insulin secretion stimulated by isoprenaline or phentolamine but not that stimulated by glucose or sulphonylureas. Complete inhibition of isoprenaline-induced hyperinsulinaemia was obtained with practolol, in a dose which was without effect on the plasma insulin elevations produced by glucose or glibenclamide. (±)-Propranolol inhibited glucose or tolbutamide-stimulated insulin secretion from chopped pancreas in vitro indicating a direct action of the drug on the pancreas. It is suggested that propranolol-induced inhibition of insulin secretion may not be entirely due to the β-adrenoceptor blocking activity of the drug.