Sperm preparation methods.

Abstract

DAVID MORTIMERFrom the Genesis Fertility Centre, Vancouver, BC,Canada.The spermatozoa of all placental (eutherian) mammals,including humans, are in a protective, nonlabile state atejaculation and are incapable of fertilization even if theyare placed in direct contact with an oocyte. Consequently,they must undergo a subsequent period of final maturationduring which they acquire the capacity to interact withthe oocyte–cumulus complex and achieve fertilization.This process, which was discovered independently byAustin and Chang in 1951, was termed capacitation, andspermatozoa in the ejaculate are prevented from under-going capacitation by one or more decapacitation factorsthat are present in the seminal plasma (Yanagimachi,1994). Capacitation of eutherian spermatozoa is essentialfor fertilization not only in vivo but also in vitro, andunderlies the manipulation of spermatozoa for clinical invitro fertilization (IVF).Not only does seminal plasma contain one or more de-capacitation factors that prevent spontaneous capacitationof spermatozoa upon ejaculation, but it also contains oneor more factors to which prolonged exposure has adverseeffects on sperm function, including the ability to pene-trate cervical mucus (Kremer, 1968), undergo the acro-some reaction in vitro, and the fertilization process in gen-eral (Rogers et al, 1983; Mortimer and Mortimer, 1992;Mortimer et al, 1998). Consequently, in order for euthe-rian spermatozoa to have the capacity to fertilize an oo-cyte, they must be separated from the seminal plasma,and hence, the separation of human spermatozoa fromseminal plasma is an essential prerequisite for them to beable to achieve capacitation and express their intrinsicfertilizing ability. In assisted reproductive technology(ART) laboratories, this need is manifested in the processcommonly referred to as ‘‘sperm washing,’’ in whichspermatozoa are somehow removed from the seminalplasma and resuspended in culture medium.Prolonged exposure ( 30 minutes) to seminal plasmaafter ejaculation can permanently diminish the fertilizingcapacity of human spermatozoa in vitro (Rogers et al,1983), and contamination of prepared sperm populationswith only traces of seminal plasma can diminish, or even