Arginine vasopressin suppresses oxytocin release from the superfused rat hypothalamo-pituitary complex

The role of arginine vasopressin (AVP) in the regulation of oxytocin secretion was studied in a superfusion system of the hypothalamo-pituitary complex from cycling female rats in dioestrus of the oestrous cycle. After perfusion with Medium 199 alone at 37 degrees C for an equilibration period of 2.5 h, perfusion with Medium 199 containing 10 mU/ml AVP for 30 min caused a prompt and significant (P less than 0.05) decrease in the oxytocin level of up to 60% of that before AVP perfusion, whereas Medium 199 containing 0.1 mU/ml AVP had no effect on oxytocin efflux. This finding suggests that AVP may be involved in the regulation of oxytocin release from the hypothalamo-pituitary system.