Capacitation

Capacitation is a process sperm must undergo to prepare to fertilize an egg. This is a process that mature spermatozoa undergo after entering the oviduct and uterus of the female reproductive tract. Sperm must undergo capacitation and the acrosome reaction to be able to penetrate through the outer layers of an oocyte, namely the cumulus ooporus and the zona pellucida. Capacitation results in hyperactivation of sperm motility, with the acrosome and cortical reaction following this. Compounds such as heparin and progesterone can be used to induce capacitation.

As a result of the sperm entering the upper female reproductive tract, the sperm are introduced to an extracellular environment that contains a cholesterol acceptor (usually serum albumin), electrolytes, and energy substrates such as glucose, pyruvate, and lactate. It is this change in environment that triggers capacitation. For purposes of in vitro fertilization, capacitation occurs by incubating spermatozoa that have been retrieved via ejaculation or extracted from the epididymis and incubated in a defined medium for several hours. There are different techniques to perform the capacitation step: simple washing, migration (swim-up), density gradients, and filter.