Adrenomedullin inhibits norepinephrine-induced contraction of rat seminal vesicle

Objective: To investigate the effect of adrenomedullin (ADM) on seminal vesicle smooth muscle contractions in the rat and the specific receptor involved. Whether it was dependent on the nitric oxidant pathway was also investigated.

Methods: The seminal vesicles from Sprague-Dawley rats aged 8-10 weeks were incubated in Kreb's solution. Using an organ bath technique, the contraction of the seminal vesicle in response to norepinephrine (NE) and ADM was recorded, in the presence or absence of an ADM receptor blocker (hADM22-52), a calcitonin-gene-related peptide (CGRP) receptor blocker (hCGRP8-37), and L-NG-nitroarginine methyl ester, an endothelial nitric oxide synthase inhibitor. The basal tone, amplitude, and frequency of contraction were measured after incubation with the drugs.

Results: The results showed that the contraction induced by NE was effectively inhibited by ADM. The basal tone, amplitude, and frequency all decreased. The ADM effects on the NE-induced increases in basal tone and amplitude were completely blocked by hCGRP8-37, the CGRP receptor antagonist, but were not abolished by L-NG-nitroarginine methyl ester.

Conclusion: The findings have demonstrated that in the seminal vesicle the inhibitory effect of ADM on NE-induced contraction was mediated by the CGRP receptor but not by nitric oxide production.