Inhibitory effect of dexamethasone on the oxytocin response to insulin-induced hypoglycemia in normal men

Glucocorticoids are known to reduce both ACTH and arginine vasopressin responses to insulin-induced hypoglycemia in normal men. The present study was undertaken in order to establish whether glucocorticoids are capable of modifying the oxytocin (OT) response to hypoglycemia. For this purpose, 8 normal men (28–33 yr) were tested with insulin (0.15 IU/kg in an iv bolus) [insulin tolerance test (ITT)] with and without pretreatment with dexamethasone (2 or 4 mg in an iv bolus 10 min before insulin). Eight different subjects (29–35 yr) were tested with dexamethasone alone. The administration of dexamethasone (2 or 4 mg) alone changed neither ACTH nor OT concentrations in the plasma during the next hour. Insulin produced similar hypoglycemic responses, regardless of dexamethasone treatment. ACTH levels rose significantly in response to insulin-induced hypoglycemia, with a mean peak response at 45 min (p<0.01 vs baseline). Two and four mg dexamethasone produced similar significant reductions of the ACTH response to hypoglycemia (p<0.02 at 45 min, p<0.05 at 30 and 60 min vs ITT). In the ITT, OT levels rose significantly in response to hypoglycemia, with a mean peak response at 45 min (p<0.01 vs basal value). The pretreatment with 2 or 4 mg dexamethasone reduced in a similar manner the hypoglycemia-induced OT rise (p<0.05 at 30 and 45 min vs ITT). These findings show a partial inhibition by dexamethasone of the OT response to hypoglycemia. In view of the possible hyperglycemic effects of OT at least in pathological conditions, such as diabetes mellitus, the inhibition by glucocorticoids of OT secretion may be supposed to play a role in the regulation of glucose homeostasis.