Capacitation

This chapter gives a summary of capacitation, which is an additional “maturation” process that spermatozoa must undergo to acquire fertilization potential. Sperm capacitation is a prerequisite for the acrosome reaction that is a release of proteolytic enzymes enabling sperm penetration through the egg coat. Capacitation can be initiated by incubating spermatozoa in any medium that retains them in a competent state, provided that it is free of seminal fluid. The removal of seminal fluid is essential, because it contains decapacitating factors that inhibit capacitation. This is possibly one of the reasons for the observation that ejaculated spermatozoa of many species are more resistant to in vitro capacitation than are epididymal spermatozoa. The inhibitory effect of seminal fluid on capacitation became evident when it was shown that on exposure to seminal fluid, capacitated spermatozoa loses both their ability to undergo induced acrosome reaction and their fertilizing potential—that is, they become “decapacitated”. This chapter finally concludes with a remark that mammalian spermatozoa should undergo two ripening stages for acquiring fertilization potential: maturation in the male reproductive tract and capacitation in the female genital tract or in vitro. Sperm motility and fertility are acquired during maturation, and the abilities to find the egg and penetrate it are acquired during capacitation. Capacitation is not involved in the actual transfer of the sperm genetic material to the egg. Its role is to prepare the conditions for such a transfer and to ensure that spermatozoa reaching the egg are those endowed with the capacity to penetrate and fertilize it.