Verapamil, a calcium antagonist, is known to inhibit glucose-induced and sulfonylurea-induced insulin release in vitro. However, there have been no reports on in vivo effects. The effect of verapamil on the peripheral IRI, blood sugar (BS) and calcium levels was investigated in thirteen normal subjects.
Verapamil, 5 mg, given to four subjects intravenously, caused a slight, but not significant, decrease in IRI, IRI/BS at thirty minutes. A fifty grams oral GTT was performed on nine subjects. Two days later, fifty grams of glucose was administered orally with verapamil 40 mg P. O. and 5 mg I. V. to the same subjects, who had been orally pretreated with 200 mg verapamil in the previous two days. Verapamil inhibited the IRI rise significantly at thirty minutes, but had no effect on BS and calcium levels at any time. The BS and IRI peaks were found at sixty minutes with the verapamil load while both peaks were found at thirty minutes during usual GTT.
These findings were consistent with in vitro studies even with the possible lower concentration of verapamil in vivo.