The significance of the blood glucose level for plasma insulin response to intravenously administered tolbutamide in healthy subjects

The effect of intravenous tolbutamide on insulin release in normal human subjects was investigated under various experimental conditions. The blood glucose level was either allowed to fall after i.v. tolbutamide or kept within normal limits by a concomitant glucose infusion. In other experiments, tolbutamide was given during different degrees of hypoglycaemia induced by insulin. It was found that tolbutamide provoked a rapid and short-lasting insulin release as well as a post-initial and extended insulin release, provided the blood glucose concentration was kept within normal limits. The hitherto accepted transiency of tolbutamide action in healthy subjects seems to be due to the hypoglycaemia which follows the administration of the drug. During more marked hypoglycaemia induced by exogenous insulin, the insulin releasing capacity of tolbutamide was almost blunted. Tolbutamide markedly enhanced the insulin release following glucose administration. The findings presented might clarify some of the therapeutic effects of the drug in diabetes mellitus.