Capacitation is the penultimate[1] step in the maturation of mammalian spermatozoa and is required to render them competent to fertilize an oocyte.
In vivo, capacitation occurs after ejaculation, when the spermatozoa leave the vagina and enter the upper female reproductive tract.
The uterus aids in the steps of capacitation by secreting sterol-binding albumin, lipoproteins, and proteolytic and glycosidasic enzymes such as heparin.
After either in vivo or in vitro capacitation the sperm must undergo the final maturation step, activation, involving the acrosome reaction.
Non-mammalian spermatozoa do not require this capacitation step and are ready to fertilize an oocyte immediately after release from the male.
[citation needed] Because assisted reproductive technologies, or ARTs, such as in vitro fertilization (IVF) or intrauterine insemination (IUI) require the induction of sperm cell capacitation outside of normal biological parameters, numerous methods have been developed to induce this process in mammalian sperm cells.
Capacitation can then be induced by adding media designed to mimic the electrolytic composition of the fallopian tubes, where fertilization occurs.
[7] Adding heparin to capacitation inducing medium mimics the secretion of heparin-like gycosaminoglycans (GAGs) near the oocyte and initiates the acrosome reaction.
A simple method uses Coomassie brilliant blue G250 to stain cells, providing visual evidence of intact or reacted acrosomes.