Properties of spermatozoa in relation to their elimination after vasectomy

Sperm disposal and the formation of sperm granulomas are two related critical aspects of vasectomy which have been studied in man and several animal models. Since mammalian spermatozoa present a keratinoid quality, a comparison was made of the resistance of human and rat spermatozoa. When exposed to dithiothreitol and sodium dodecyl sulfate, human sperm decondense readily while rat sperm resist decondensation for long periods of time. A cooperative effect in the rate of decondensation was observed for human sperm but not for rat sperm. Oxidation of sulfhydryl groups renders human spermatozoa as resistant as rat spermatozoa, indicating that disulfide crosslinks are involved in this resistance. Human spermatozoa constitute a heterogeneous population with respect to sulfhydryl group content, suggesting variations in the state of maturation and/or elimination. The sulfhydryl group content of rat epididymal spermatozoa was similar from one cell to another, suggesting little sperm reabsorption in the epididymis. Human and rat spermatozoa differ in size, resistance to decondensing agents, cooperative effect during decondensation, and content and localization of sulfhydryl groups; these differences can explain why vasectomized rats invariably develop huge granulomas while this side effect is not severe in vasectomized men.