Effects of α1-, α2- and β-adrenoceptor blockers on insulin secretion in the rat

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Abstract
The effects of .alpha.- and .beta.-adrenoceptor blockade on plasma concentrations of insulin and glucose were studied in the anesthetized rat. Infusion of the .alpha.1-adrenoceptor blocker prozosin (80 .mu.g/min), the .alpha.2-adrenoceptor blocker yohimbine (15 .mu.g/min) or the non-selective .alpha.-adrenoceptor blocker phentolamine (15 .mu.g/min) during 50 min increased plasma insulin levels by about 1.5-2.5 ng/ml. The effects of phentolamine and prazosin on circulating insulin persisted throughout the infusion; the effect of yohimbine seemed to be more transient. Plasma glucose levels increased slightly during infusion of prazosin, but tended to decrease in response to phentolamine and yohimbine. The .beta.-adrenoceptor blocker propranolol (15 .mu.g/min) lowered basal plasma insulin and glucose levels. It also depressed plasma insulin during infusion of all 3 .alpha.-adrenoceptor blockers without any appreciable influence on plasma glucose. Apparently, both .alpha.1- and .alpha.2-adrenoreceptor as well as .beta.-adrenoceptors are involved in the regulation of basal insulin secretion in the rat.