EFFECT OF RESIDUAL ENDOGENOUS INSULIN-SECRETION ON THE ABNORMAL OXYTOCIN RESPONSE TO HYPOGLYCEMIA IN INSULIN-DEPENDENT DIABETICS

Objectives. Arginine-vasopressin (AVP) and oxytocin (OT) secretions ar e abnormally stimulated by hypoglycaemia in patients with IDDM. Since previous studies showed that AVP secretion is influenced by the persis tence of residual endogenous insulin secretion, we wondered whether th is factor also regulates OT secretion. Design. Case-control study: the OT response to insulin-induced hypoglycaemia was measured in normal a nd diabetic patients with or without residual endogenous insulin secre tion. Subjects. Ten normal male subjects, 10. C-peptide positive (CpP) and 11 C-peptide negative (CpN) male diabetic patients. Tests. Prelim inary studies: plasma C-peptide levels were measured after intravenous administration of 1 mg glucagon. Insulin tolerance test (ITT): diabet ics were studied after optimization of their metabolic status by 3 day s of treatment with constant subcutaneous insulin infusion. CpP and Cp N diabetics and normal controls were tested with an intravenous admini stration of 0.15 IU per kg body weight insulin. Blood samples for OT a ssay were taken just before the rapid injection of insulin (time 0) an d at time 15, 30, 45 and 60 min. Results. The basal concentrations of OT were similar in all groups. Insulin induced a similar hypoglycaemic nadir in all groups at 30 min, even though diabetic groups showed a d elayed recovery in blood glucose levels. The glycaemic pattern was sim ilar in all diabetic patients. Hypoglycaemia-induced OT rise was signi ficantly higher in the two diabetic groups than in the normal group. H owever, CpN patients showed significantly higher OT increments than Cp P subjects.Conclusions. These data indicate that a residual endogenous insulin secretion exerts a partial protective action against the hypo thalamic-pituitary disorder affecting the OT secretory system in IDDM.