The spermatozoa of most invertebrates (e.g., sea urchins) and nonmammalian vertebrates (e.g., fishes and amphibians) have full capacity to fertilize eggs upon leaving the testis. Testicular spermatozoa of mammals, on the other hand, do not possess the ability to do so. Their fertilizing capacity develops as they pass through the epididymis (Young, 1931; Nishikawa and Waide, 1952; Blandau and Rumery, 1964; Bedford, 1966; Orgebin-Crist, 1967). This process, apparently “unique” to mammals, is referred to as the epididymal maturation of spermatozoa. Even after their maturation, however, spermatozoa require an additional phase of maturation or capacitation within the female genital tract before they are able to fertilize eggs (Austin, 1951, 1952; Chang, 1951a). Thus, epididymal maturation and capacitation are two extra steps that mammaliam spermatozoa must take before they can effect fertilization. In this chapter, I will discuss how mammalian spermatozoa prepare themselves for fertilization and how the spermatozoa and eggs interact during fertilization. The process and mechanisms of sperm transport in the female genital tract will not be dealt with extensively here. Readers are referred to Bishop (1961, 1969), Blandau (1969), Bedford (1970b, 1972b), Thibault (1972, 1973a), Zamboni (1972), Blandau and Gaddum-Rosse (1974), Hafez and Thibault (1975), Overstreet and Katz (1977), Overstreet and Cooper (1978, 1979b), Overstreet et al. (1978), Shalgi and Kraicer(1978), Cooper et al. (1979) and Hunter (1975, 1980). The rejection or elimination of extra spermatozoa by the fertilized egg, one of the most fascinating events in fertilization, will not be discussed here. Instead, readers are referred to the chapter by Dr. Wolf in this volume. The physiology of egg activation has been described and discussed to some extent by Gwatkin (1977) and Yanagimachi (1978a). There are numerous reviews dealing with general aspects of mammalian fertilization. The following are recommended to aid in grasping the outline of mammalian fertilization: Austin and Bishop (1957), Austin and Walton (1960), Austin (1961, 1968), Blandau (1961), Piko (1969), Thibault (1969), Bedford (1970a,b, 1972b), Gwatkin (1976, 1977), Yanagimachi (1977, 1978a), Bedford and Cooper (1978) and Hunter (1980).

Mechanisms of Fertilization in Mammals

https://pubag.nal.usda.gov/download/34158/PDF

Physiology of spermatozoa at high dilution rates: the influence of seminal plasma.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mrd.1120100210

Zona‐free hamster eggs: Their use in assessing fertilizing capacity and examining chromosomes of human spermatozoa

Intrauterine insemination: a critical review.

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

https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.1939-4640.2000.tb03390.x

Kuldip C. Kanwar

Papers

Effects of human seminal plasma on fertilizing capacity of human spermatozoa.