Effect of kininase II inhibitors on bradykinin-stimulated bovine sperm motility

It has been found that the enzyme kininase II present in the seminal plasma inactivates the kinins produced by the kallikreins, thus blocking their beneficial effects on the motility of post-ejaculated mammalian spermatozoa. In this study we examined the influence of 2 kininase II inhibitors (captopril and enalapril maleate) on bradykinin-induced bovine sperm motility. Ejaculates were collected from Holstein-Friesian bulls, and semen samples exhibiting reduced sperm motility (30 to 60%; mean 53 +/- 3.8%) were used. Each semen sample was divided into 6 portions: 1) control; 2) treated with bradykinin (M-8); 3) treated with captopril (M-2); 4) treated with enalapril maleate (M-3); 5) treated with bradykinin + captopril; and 6) treated with bradykinin + enalapril maleate. Total sperm motility was recorded over 4 h at 1-h intervals. It was found that in the second hour after treatment both the combinations of bradykinin + captopril and bradykinin + enalapril maleate considerably enhanced sperm motility compared with that of the controls (P < 0.01 and P < 0.05, respectively). Total sperm motility rates of semen samples treated with these combinations were also higher than in the samples treated either with inhibitors alone or with bradykinin alone. We concluded that the stimulatory effect of bradykinin on bovine sperm motility was considerably potentiated and prolonged by the addition of the kininase II inhibitors.