title: Sensitivity of insulin secretion to feedback inhibition by hyperinsulinaemia.
abstract: The ability of insulin to inhibit its own secretion was examined in 15 normal subjects given an intravenous infusion of insulin in a dose of 0.25, 0.50, 1.0, 5.0 or 10.0 mU/kg/min for two hours. Arterial plasma insulin concentration achieved during the infusion segregated into three levels of hyperinsulinaemia: 35 +/- 1 (mean +/- SEM), 87 +/- 15 and 828 +/- 210 muU/ml. Plasma glucose concentration was kept constant at the basal level by a variable glucose infusion. Fasting C-peptide (0.29 +/- 0.02 pmol/ml) fell significantly in all subjects during hyperinsulinaemia and reached a concentration of 0.19 +/- 0.03 pmol/ml at 60 min and 0.14 +/- 0.03 at 120 min after the start of the insulin infusion. The C-peptide response was not related to the infusion dose nor to the steady state plasma insulin concentration. It is concluded that (a) basal insulin secretion as evaluated from C-peptide measurements is inhibited by small (24 +/- 3 muU/ml) physiological elevations in plasma insulin concentration independent of changes in plasma glucose, and (b) supraphysiological or even pharmacological elevations in plasma insulin do not result in a further decrease in endogenous insulin secretion above that achieved with mild hyperinsulinaemia.
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000032:analysis; D002096:C-Peptide / Q000097:blood; D006801:Humans; D007263:Infusions, Parenteral; D007328:Insulin / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D000078790:Insulin Secretion; D008297:Male
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin