Action of pro-opiomelanocortin products on the rat vas deferens

Behavioral study of pro-opiomelanocortin products indicates that beta-endorphin and corticotrophin-like peptides have antagonistic effects. However, these peptides have similar actions on the rat vas deferens. beta-endorphin, alpha-MSH and ACTH each inhibit electrically evoked contraction of the duct, but the corticotrophin derived peptides are tenfold more potent on a molar basis (ED50 = 9 nM). Pharmacological analysis shows that the action of corticotrophin-derived peptides does not involve an opiate receptor mechanism. The results are discussed in terms of the central action of the peptides.