ULTRASTRUCTURAL-LOCALIZATION OF ANGIOTENSIN-CONVERTING ENZYME IN EJACULATED HUMAN SPERMATOZOA

Angiotensin-converting enzyme (ACE) is known to be released from human spermatozoa during capacitation, However, it has not yet been localiz ed ultrastructurally in ejaculated sperm cells. Therefore, the purpose of the present study was to demonstrate the location of ACE by means of immunoelectron microscopy and direct immunofluorescence. In additio n, ACE activity of spermatozoa was correlated with standard semen para meters. The activity of angiotensin-converting enzyme was measured in spermatozoa from 115 donors and patients attending the andrological ou tpatient department. Progressive motility was negatively correlated wi th sperm ACE activity (Spearman rank correlation r = -0.364, P < 0.000 1), whereas no statistically significant correlations with sperm conce ntration, total motility and morphology were observed. Immunoelectron microscopy demonstrated that ACE is mainly located at the plasma membr ane of the acrosomal region, equatorial segment, postacrosomal region and midpiece, In contrast, only weak ACE-like immunoreactivity was fou nd at the flagellum, In cases of cells with missing plasma membranes A CE seems also to be located at the surface of the outer acrosomal memb rane. By means of immunohistochemical methods, different patterns of A CE-like immunofluorescence were observed: (i) fluorescence of the acro some or the entire sperm head, midpiece and flagellum; (ii) fluorescen ce of the postacrosomal region, midpiece and flagellum; (iii) bright f luorescence of the equatorial segment with less intensive labelling of the postacrosomal region and flagellum, Induction of the acrosome rea ction by calcium ionophore A23187 resulted in an increase of spermatoz oa with weak acrosomal fluorescence, indicating loss of the plasma mem brane.