Influence of verapamil on human glucose tolerance.

Studies have indicated that verapamil inhibits insulin release from pancreatic beta cells in vitro. Studies in this clinic, however, showed that both oral pretreatment with verapamil for 1 week and intravenous infusion of the drug over a period of 3 hours improved oral glucose tolerance in patients with type II diabetes without affecting insulin release. In contrast, verapamil failed to increase further the hypoglycemic effect of oral glibenclamide therapy when administered intravenously in diabetic patients. This hypoglycemic effect of verapamil does not appear to be caused by reduced glucose absorption from the gut because intravenous infusion of verapamil left the portal vein glucose response to glucose ingestion unaffected in normoglycemic patients who underwent portal vein catheterization for diagnostic purposes. It is more likely that verapamil affects the liver, leading to decreased hepatic glucose output, which supports previous reports that have shown an inhibitory influence of verapamil on enzymes involved in the gluconeogenetic and glycogenolytic processes.