Enkephalin-degrading enzymes in normal and subfertile human semen.

ABSTRACT: Opioid peptides have been reported to have impor-tant functions in human reproduction. Indeed, very high concentra-tions of enkephalins and their degrading enzymes have been re-ported in human semen. In the present paper, we compare theactivity of two enkephalin-degrading enzymes, aminopeptidase Nand neutral endopeptidase 24.11, in different fractions of semenfrom normozoospermic, fertile men and from subfertile patientswith different abnormalities revealed by spermiogram analysis (as-thenozoospermia, necrozoospermia, and teratozoospermia). Highlevels of activity of aminopeptidase N were found in the solubleand particulate sperm fractions of semen from patients presentingasthenozoospermia with necrozoospermia. In contrast, lower ami-nopeptidase N activity was measured in the soluble sperm fractionof asthenozoospermic semen. The percentage of dead spermato-zoa was positively correlated with aminopeptidase N activity inboth soluble and particulate sperm fractions. In contrast, the per-centage of immobile spermatozoa was negatively correlated withaminopeptidase activity in soluble and particulate sperm, and inprostasome fractions. Levels of activity of neutral endopeptidasewere found to be unaltered among the different conditions. In sum-mary, the results of the present study indicate that alterations inthe activity of aminopeptidase N may be one of the molecular com-ponents that contribute to male human subfertility.Key words: Opioid peptide, peptidase, seminal fraction, spermmotility, sperm death.J Androl 2004;25:733–739