Embryo development capacity of oocytes fertilized by immature sperm and sperm treated with motility stimulants.

The fertilizing ability of mouse spermatozoa develops during maturation and coincides with the acquisition of motility. The lack of progressive motility of spermatozoa from the testis and precaudal segments of the epididymis interferes with their ability to fertilize oocytes after insemination in vitro. The removal of cumulus cells for insemination in vitro and the use of subzonal injection of a single spermatozoon resulted in a higher number of oocytes fertilized by immature caput and corpus spermatozoa. High rates of embryonic arrest and retarded development were observed in oocytes fertilized by caput and corpus spermatozoa when compared with oocytes fertilized by cauda spermatozoa. However, when the oocytes were enclosed in their cumulus cells or microinjected with a single spermatozoon, these effects were reduced. A block in embryonic development was also observed after human and mouse oocytes were exposed to the sperm motility stimulants pentoxifylline (PTF) and 2-deoxyadenosine (DOA). These observations suggest that exposure of oocytes to PTF and DOA should be avoided.