Calcium antagonists and hormone release. I. Effects of verapamil on insulin release in normal subjects and patients with islet-cell tumor.

Intravenous infusion of verapamil, an organic antagonist of calcium transport into cells, produced a marked and significant inhibition of glucose-, glucagon- and sulfonylurea-induced increases in serum insulin in normal subjects. Also, blood glucose concentrations remained significantly higher after the secretagogue plus verapamil than after the secretagogue alone. Blood glucose concentrations increased regularly after verapamil + glucagon administration indicating that verapamil is not capable of inhibiting the hepatic glycogenolysis induced by glucagon. Two patients with islet-cell tumor, treated with verapamil for 5 days, experienced a decrease in the severity and frequency of hypoglycemic attacks while "autonomous" insulin release was inhibited. The present results clearly show that calcium antagonists are capable of inhibiting insulin response to appropriate stimuli in normal subjects. Therapeutic association of calcium antagonists and sulfonylureas should be used with caution in the light of the present findings. Calcium antagonists can be useful drugs in the treatment of hypoglycemia caused by islet-cell tumor.