Objective:To study the effect of inter medin(IMD) on smooth muscle of rat seminal vesicles including the specific receptors and the signal pathways involved.Methods:The contraction of the seminal vesicle in response to norepinephrine(NE) andADM2/IMD was studied by the organ bath method.The effects of antagonists for calcitonin gene related peptide(CGRP), adrenomedullin(ADM) andIMD receptors, and inhibitors of nitric oxide synthase, [L-NG-NitroarginineMethylEster,L-NAME) and cAMP-dependent protein kinase(PKA),KT5720] were also investigated.The first overshoot, amplitude, frequency and basal tone were measured. Results:There is no significant effect ofIMD on the initial overshoot, frequency and the basal tone in the seminal vesicle contraction.Only the amplitude of the contraction induced byNE was inhibited byIMD.TheIMD inhibitory actions on amplitude were completely blocked by hADM22-52 andL-NAME, but not by hCGRP8-37 orKT5720.Furthermore, the action was diminished byIMD17-47.Conclusion:The results demonstrated that the inhibitory action ofIMD onNE-induced seminal vesicle contraction was mediated via theADM receptor(s) and the nitric oxide production pathway, partially by theIMD receptor, but not by theCGRP receptor and the cAMP-PKA pathway.