740 



SPERM, OVA, AND PREGNANCY 



the spermatozoa during capacitation, ear- 

 lier suppositions leaned toward the view that 

 something is lost or gained by the gametes 

 which results in enzyme activation recjuired 

 for fertilization (Austin and Bishop, 1957). 

 It has since been suggested that the change, 

 in rat sperm at least, involves processes lead- 

 ing to the disintegration or loss of the acro- 

 some from the sperm head, thereby exposing 

 structures responsible for egg penetration 

 (Austin and Bishop, 1958a, b). The revers- 

 ible counteraction of capacitation by rabbit 

 seminal plasma, demonstrated by Chang 

 (1957), casts some doubt, however, on the 

 likelihood of pronounced structural changes 

 occurring during this phase of si:)erm matu- 

 ration. Until the physiologic changes respon- 

 sible for the suggested morphologic altera- 

 tions are clarified, the mechanism of 

 capacitation will remain obscure. 



F. DUR.\TION OF SPERM MOTILITY THROUGHOUT 

 THE TRACT 



The viability of spermatozoa in the am- 

 pulla, assessed by motility, outlasts their 

 fertilizing capacity (Table 13.8). Elsewhere 

 in the tract, motility serves as a criterion for 

 sperm longevity, and considerable variation 

 in the ability of separate segments of the 

 tract to support it has been demonstrated. 

 Rat spermatozoa, for example, survive in 

 the cornua about 12 hours, compared with 

 16 or 17 hours in the oviducts (White, 

 1933a) . Sperm motility in the human fundus 

 appears to be less than that in the Fallopian 

 tube (Farris, 1950; Rubenstein, Strauss, 

 Lazarus and Hankin, 1951). 



In most mammals the alkaline cervical 

 mucus sustains motility well, whereas the 

 acidic vaginal depository is detrimental. Mo- 

 tile spermatozoa have been reported in hu- 

 man cervical mucus a week after coitus, al- 

 though the average duration of motility 

 here is closer to 2 days. The duration of 

 motility in cervical mucus varies with the 

 cycle, maximal motility coinciding with the 

 time of ovulation (Beshlebnov, 1938; Cohen 

 and Stein, 1951). Estrogen-induced hyper- 

 secretion of mucus is claimed to increase 

 sperm viability as well as penetrability. 

 Longevity in the cervical mucus of the es- 

 trous macaque is approximately 24 hours. 



The primate vagina is notably inhospita- 



ble to spermatozoa, presumably because of 

 its high acidity. Motility is sustained in the 

 human vagina rarely longer than 3 to 4 

 hours (Weisman, 1939), and the duration is 

 believed to vary inversely wdth changes in 

 vaginal acidity (pH 4 to 5). The human 

 vaginal pH, curiously enough, has been 

 claimed to reach a minimum at the time of 

 ovulation, an overt sign, according to 

 Schockaert, Delrue and Ferin (1939), of 

 high estrogenic activity (Fig. 13.11 ). On the 

 other hand, a sharp rise in vaginal pH of 

 approximately 0.5 unit was claimed by Zuck 

 and Duncan (1939) to be coincident with 

 ovulation; this elevation is inconstant and, 

 when it does occur, may be due to the pres- 

 ence of alkaline cervical mucus. Normally, 

 in the cow, the influx of mucus renders the 

 vagina alkaline at estrus (Lardy, Pounden 

 and Phillii)s, 1940). Under normal circum- 

 stances, the inseminate is only briefly, if at 

 all, exposed to the vaginal medium. When 

 not ejaculated directly into the cervix or 

 uterus, the semen may be conducted rap- 

 idly toward the cervical canal by longi- 

 tudinal contraction waves (Noyes, Adams 

 and Walton, 1958). It is doubtful, therefore, 

 whether the high hydrogen-ion concentra- 

 tion, characteristic of the vagina, is of any 

 great significance in the reproductive econ- 

 omy of most mammals. 



G. SPERM VIABILITY IX RELATION TO 

 TUBAL PHYSIOLOGY 



In view of the great wealth of information 

 concerning uterine and tubal transport and 

 sperm survival, on the one hand, and uterine 

 function and hormonal responses, on the 

 other, there has been an appalling lack of in- 

 terest in the nature of the genital fluids and 

 the immediate environment surrounding the 

 spermatozoa during their sojourn within the 

 female genital tract. The corresponding defi- 

 ciency of our knowledge of the male genital 

 tract was previously noted. Difficulties in 

 technique exist, to be sure, but they are far 

 from insurmountable, and rich rewards 

 should result from exploration in this virgin, 

 but obviously fertile, field. 



A review of the extensive literature on the 

 cytochemistry of the endometrium and tubal 

 epithelium and on the changes with varia- 

 tions in the estrous cycle reveals consider- 



