Sperm Capacitation and Fertilization in Mammals

Abstract

Current evidence and speculations concerning the nature of sperm capacitation in mammals are reviewed and critically assessed. Capacitation, a subtle functional change which must occur at least in some mammals before fertilization can take place, occurs in sperm as a result of exposure to secretions of the female tract. In some species the noncapacitated state may enable sperm to undergo a period of storage in the cauda epididymidis after completion of maturation in the mate; alternatively, the noncapacitated state may enable sperm to withstand exposure to the female tract for some time before the arrival of the egg. In several species evidence indicates capacitation enables sperm to penetrate the cumulus oophorus and the zona pellucida. Capacitation may involve changes on the sperm surface, such as the unmasking of so-called receptor sites. Both the uterus and the fallopian tube play a part in capacitation. Contraception via capacitation control by steroid therapy alone is unlikely to be achieved. The question of the need for capacitation in man is as of yet resolved. Areas reviewed include need for capacitation in different mammals, analysis of factors important for capacitation, changes in sperm during capacitation, and events involved in fertilization. Species for which definite evidence of capacitation has been found include the rat, rabbit, hamster, ferret, and sheep.