A new Met-enkephalin analogue suppresses plasma vasopressin in man.

Metkephamid acetate, a newly synthetized analogue of methionine enkephalin, suppressed plasma vasopressin levels from 2.4 pg/ml to 0.8 pg/ml after intramuscular administration to 4 normal human volunteers. This suppression occurred in the absence of significant changes in either plasma osmolality or blood pressure. Thus, metkephamid acetate, like many other opiates which bind to the mu subtype of opiate receptors, has a direct suppressive effect on plasma vasopressin levels.