During mammalian spermiogenesis, replacement of the somatic histones by basic proteins, the protamines, allows normal sperm nuclear condensation. In this study we have evaluated the degree of chromatin compaction in spermatozoa from 191 infertile subjects, affected by different testicular disorders, compare with that in 50 fertile sperm donors (controls). In infertile men, there was a higher percentage of unstable spermatozoa after incubation with sodium dodecyl sulphate (SDS) and of stained spermatozoa after staining with aniline blue (P less than 0.001 vs. controls). Furthermore, a positive linear correlation was found between SDS-unstable spermatozoa and stained spermatozoa (P less than 0.001), suggesting that sperm instability was related to a defect in histone-replacement by sperm-specific nucleoproteins, protamines. When the patients were considered according to pathology, high sperm nuclear instability and a high percentage of stained spermatozoa were detected in groups affected by varicocele, idiopathic infertility and in patients with a history of unilateral cryptorchidism. In the latter group the same alterations were observed even when the cryptorchid testis had been removed during surgery. In the group with a past history of mumps orchitis these parameters did not show any difference when compared with controls.

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Recently it has been observed that ejaculated human sperm possess high angiotensin converting enzyme (ACE) activity and that this enzyme is released during the process of capacitation. This observation raises the possibility that ACE may be involved in the fertilization process. To verify this hypothesis, we tested the effects of a potent ACE inhibitor, Captopril, on acrosome reaction induced by capacitating medium (3.5% HSA-added BWW) and on ability of human capacitated spermatozoa to penetrate zona-free hamster oocytes. Addition of Captopril (100 nmol l-1) modified neither sperm motility nor viability at any time considered, but significantly reduced the acrosome reaction percentages of sperm incubated in capacitating medium. Furthermore, Captopril significantly reduced the percentage of penetrated oocytes. The mean penetration rates both in the absence and presence of Captopril were 65.5 +/- 4.9% and 26.9 +/- 2.3% (P less than 0.001) respectively. These findings provide evidence that sperm release of ACE during capacitation may have a physiological role in the regulation of the mechanisms that allow sperm acrosome reaction and thus fertilizability.

In azoospermic subjects, testicular cytological analysis permits the identification of different sub-types and this classification may be very important in determining therapy, particularly the choice between surgical treatment and the hypothetical use of assisted fertilization techniques by retrieval of epididymal or intratesticular spermatozoa or spermatids.