Characterisation of the effect of intravenous infusion of glucose and tolbutamide on the insulin delivery rate in man.

Serum insulin response to a single bolus of IV glucose or tolbutamide was measured in eight healthy subjects. Insulin disappearance rate was assessed by deconvolution from the serum insulin levels, using the measured insulin disappearance rate. The mean rate constant of insulin disappearance was 0.238 +/- 0.005 min-1 (mean +/- SEM). Basal insulin delivery rate was 8.0 to 9.0 mU/min and the delivery rate following glucose injection (0.5 g/kg body weight) showed a biphasic response, whereas that after tolbutamide injection (15.6 mg/kg body weight), a monophasic response. After glucose injection, 1.7 +/- 0.3 U of insulin was delivered during the first phase (0--10 min) and 5.6 +/- 1.6 U during the second phase (11--60 min). After tolbutamide injection, 1.5 +/- 0.3 U of insulin was delivered during the first 10 min. Between 11 and 40 min, 1.6 +/- 0.5 U of insulin was delivered. The results thus confirm and also quantitate biphasic insulin secretion after a bolus of glucose with a monophasic response after tolbutamide. The method is suitable for studies of the insulin secretogogues in man.