Sperm Preparation Methods

Abstract

The spermatozoa of all placental (eutherian) mammals, including humans, are in a protective, nonlabile state at ejaculation and are incapable of fertilization even if they are placed in direct contact with an oocyte.Consequently, they must undergo a subsequent period of final maturation during which they acquire the capacity to interact with the oocyte-cumulus complex and achieve fertilization.This process, which was discovered independently by Austin and Chang in 1951, was termed capacitation, and spermatozoa in the ejaculate are prevented from undergoing capacitation by one or more decapacitation factors that are present in the seminal plasma (Yanagimachi, 1994).Capacitation of eutherian spermatozoa is essential for fertilization not only in vivo but also in vitro, and underlies the manipulation of spermatozoa for clinical in vitro fertilization (IVF).Not only does seminal plasma contain one or more decapacitation factors that prevent spontaneous capacitation of spermatozoa upon ejaculation, but it also contains one or more factors to which prolonged exposure has adverse effects on sperm function, including the ability to penetrate cervical mucus (Kremer, 1968), undergo the acrosome reaction in vitro, and the fertilization process in general (Rogers et al, 1983;Mortimer and Mortimer, 1992;Mortimer et al, 1998).Consequently, in order for eutherian spermatozoa to have the capacity to fertilize an oocyte, they must be separated from the seminal plasma, and hence, the separation of human spermatozoa from seminal plasma is an essential prerequisite for them to be able to achieve capacitation and express their intrinsic fertilizing ability.In assisted reproductive technology (ART) laboratories, this need is manifested in the process commonly referred to as ''sperm washing,'' in which spermatozoa are somehow removed from the seminal plasma and resuspended in culture medium.Prolonged exposure (30 minutes) to seminal plasma after ejaculation can permanently diminish the fertilizing capacity of human spermatozoa in vitro (Rogers et al, 1983), and contamination of prepared sperm populations with only traces of seminal plasma can diminish, or even