Sheep testicular and epididymal angiotensin converting enzyme: Inhibitions by captopril, lisinopril and enalapril

Inhibition of angiotensin converting enzyme (ACE) in presence of captopril (C), lisinopril (L) and enalapril (E) were investigated in testis and epididymis of sheep using Hip-His-Leu as substrate. Captopril, lisinopril and enalapril were competitive inhibitors of the enzyme from both tissues. Differences in the I₅₀ and K(i) values using these three inhibitors reflects the affinities of these inhibitors for the ACE. In addition, the relative potencies of captopril, lisinopril and enalapril were different for testicular ACE (C > L > E) and epididymal ACE (L > C > E). This observation suggests differences between the active sites of the testicular and epididymal ACE which may reflect on their functions in vivo.