Adrenomedullin inhibits the contraction of cultured rat testicular peritubular myoid cells induced by endothelin-1.

The present study documents that adrenomedullin (AM), a vasoactive peptide originally identified in pheochromocytoma tissue and present in the testis, in vitro affects the function of testicular peritubular myoid cells (TPMC), a contractile cell type located in the seminiferous tubule wall. AM stimulated cAMP production by cultured TPMC taken from 16-day-old rats, and this effect was completely inhibited by the AM antagonist AM-(22-52) and partially by the CGRP (calcitonin gene-related peptide) antagonist CGRP-(8-37). Studies on TPMC contractile activity documented that AM inhibits TPMC contraction induced by endothelin-1 (ET-1) and that its effect is antagonized by AM-(22-52). Neutralizing AM produced by TPMC with the addition of anti-AM antibody induced a significant increase of ET-1-induced contraction. When exposed to the protein kinase A inhibitor H-89, AM inhibitory activity on ET-1-induced TPMC contraction was suppressed, whereas the nitric oxide synthase inhibitor N:(G)-nitro-L-arginine methyl esther did not modify AM activity. In conclusion, our study indicates that AM stimulates cAMP production and inhibits the contraction induced by ET-1 in TPMC in vitro, and that AM produced by TPMC has an autocrine effect. We propose that AM may have a role in the control of seminiferous tubule contraction.