EXPRESSION AND LOCALIZATION OF ENDOTHELIN-CONVERTING ENZYME IN RAT VAS-DEFERENS

Endothelins (ETs) are a family of vasoconstrictor and mitogenic peptid es originally isolated from the endothelial cells. Three isoforms of E T, namely ET-1, ET-2 and ET-3, are generated from their respective int ermediate precursors big ETs through specific endoproteolytic cleavage by endothelin converting enzyme (ECE). Using reverse-transcription po lymerase chain reaction (RT-PCR), we have isolated a cDNA encoding for ECE from both the prostatic and epididymal halves of rat vas deferens . In situ hybridization using digoxigenin-labeled ECE cDNA probe demon strated that ECE mRNA is preferentially localized in the inner longitu dinal smooth muscle layer adjacent to submucosa region of rat vas defe rens. Both ET-1 and big ET-1 at 30 nM potentiated electrically stimula ted contractile response of prostatic vas deferens. Pre-incubation of tissue with a metalloprotease ECE inhibitor phosphoramidon (10 mu M) s trongly inhibited the response to big ET-1, but not to ET-1. On the ot her hand, big ET-1 failed to elicit contractile response of epididymal vas deferens. Phosphoramidon alone did not affect both the basal and electrically stimulated contractile responses in vas deferens. These d ata indicate that the circulating ET-1 and its immediate precursor big ET-1 could differentially regulate smooth muscle contractions in the prostatic and epididymal vas deferens of the rat.