Volpi R, Chiodera P, Capretti L, Caffarri G, Giuliani N, Caiazza A, Coiro V (University of Parma, Hospital of Codogno, Hospital of Guastalla, Hospital of Fidenza, Italy). Effect of residual endogenous insulin secretion on the abnormal oxytocin response to hypoglycaemia in insulin-dependent diabetics. J Intern Med 1998; 244: 43–8. Objectives Arginine-vasopressin (AVP) and oxytocin (OT) secretions are abnormally stimulated by hypoglycaemia in patients with IDDM. Since previous studies showed that AVP secretion is influenced by the persistence of residual endogenous insulin secretion, we wondered whether this factor also regulates OT secretion. Design Case-control study: the OT response to insulin-induced hypoglycaemia was measured in normal and diabetic patients with or without residual endogenous insulin secretion. Subjects Ten normal male subjects, 10 C-peptide positive (CpP) and 11 C-peptide negative (CpN) male diabetic patients. Tests Preliminary studies: plasma C-peptide levels were measured after intravenous administration of 1 mg glucagon. Insulin tolerance test (ITT): diabetics were studied after optimization of their metabolic status by 3 days of treatment with constant subcutaneous insulin infusion. CpP and CpN diabetics and normal controls were tested with an intravenous administration of 0.15 IU per kg body weight insulin. Blood samples for OT assay were taken just before the rapid injection of insulin (time 0) and 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 delayed recovery in blood glucose levels. The glycaemic pattern was similar in all diabetic patients. Hypoglycaemia-induced OT rise was significantly higher in the two diabetic groups than in the normal group. However, CpN patients showed significantly higher OT increments than CpP subjects. Conclusions These data indicate that a residual endogenous insulin secretion exerts a partial protective action against the hypothalamic-pituitary disorder affecting the OT secretory system in IDDM.
