Sperm nuclear instability and staining with aniline blue: abnormal persistence of histones in spermatozoa in infertile men.

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.