Ultrastructural study on cytotoxic effects of cyclosporine A in spermiogenesis in rats.

Cyclosporine A (CsA) is known to have testicular toxicity, leading to male infertility. The occurrence of numerous anomalous spermatids and residual bodies in the epididymal ducts of rats treated with CsA was observed in our previous studies. To examine the fine structural changes of impaired spermiogenesis induced by CsA, rats were treated s.c. with 40 mg/kg/day CsA for 2 weeks. Desquamation of round spermatids still surrounded by a slender Sertoli cell cytoplasm was occasionally observed. A prominent change in the seminiferous tubules was an occurrence of numerous residual bodies containing one or more flagella. They were not phagocytosed by the Sertoli cell, and accumulated in the epididymal ducts. Cellular components in the epididymal lumen included degenerating round spermatids and abnormal spermatozoa and residual bodies. Although separation of the head from the tail of the spermatozoa was rarely seen, various kinds of abnormalities of flagella were frequently encountered; compact aggregation of numerous flagella in a single spermatozoon or residual body, disarrangement of mitochondrial or fibrous sheath with outer dense fibers, and fusion of flagella with a single intervening mitochondrial layer. These findings indicate that CsA gives rise to toxic effects on the spermiogenesis by impairing directly the spermiogenic cell development and by impeding Sertoli cell function including a reduction of its phagocytic activity.