Release of vasopressin by enkephalin

Leu-enkephalin, its stable analogue [D-Ala2-D-Leu5]-enkephalin and the C-fragment of lipotropin (beta endorphin) injected intravenously in the rat produced antidiuretic responses which were inhibited reversibly by naloxone. It was shown for Leu-enkephalin that injection into the cerebral ventricles was at least ten times more effective than intravenous injection and for [D-Ala2-D-Leu5]-enkephalin that the antidiuretic response was associated with increased excretion of vaspressin in the urine.