Improvement of glucose tolerance by verapamil in patients with non-insulin-dependent diabetes mellitus.

To study the effect of verapamil on the glucose tolerance and insulin response to oral glucose, 6 healthy subjects and 15 patients with non-insulin-dependent diabetes mellitus (NIDDM) were performed on separate days: 1) A standardized oral glucose load, 2) an identical glucose load during i.v. infusion of verapamil, and 3) a third oral glucose load after one week of oral verapamil treatment. No significant differences were found when the insulin and glucose responses with and without verapamil were compared. The patients with NIDDM were divided into three groups. Two tests were performed on separate days in each patient: group 1, a standardized oral glucose load and an identical glucose load during i.v. verapamil infusion; group 2, a standardized oral glucose load and a similar glucose load after one week of oral verapamil treatment; group 3, the protocol of group 2 was followed but oral placebo was given instead of verapamil. In groups 1 and 2, verapamil improved the tolerance for oral glucose, whereas the insulin response remained unaffected. In group 3, no significant differences were found in the insulin and glucose responses to the two oral glucose loads. These findings thus imply that verapamil improves the tolerance for oral glucose regardless of the route of verapamil administration in patients with NIDDM. They also indicate that this is accomplished by an effect of verapamil on other glucose regulatory factors than insulin.