732 



SPERM, OVA, AND PREGNANCY 



secretions, pronounced at the time of ovula- 

 tion (Bishop, 1956a), serve as vehicle of 

 transport for the sperm. The copious uterine 

 fluid secreted in the rat during tlie proestrum 

 performs the same role (Warren, 1938). 



It is probable that ciliary activity plays 

 a greater role in some animals than in others 

 in distributing sperm throughout the female 

 tract. Thus, Parker ( 1931 ) stressed the im- 

 portance of adovarian ciliary currents in the 

 oviducts of the turtle, pigeon, and chicken. 

 With respect to a6ovarian currents, more- 

 over, it should be pointed out that these, too, 

 could serve a function by orienting the sperm 

 toward the infundibulum ; whereas unneces- 

 sary emphasis should not be placed on this 

 as a transport mechanism, considerable evi- 

 dence exists to show that sperm orient 

 against a current and, when free-swimming, 

 make considerable progress upstream (Adol- 

 phi, 1906a, b; Yamane and Ito, 1932; von 

 Khreninger-Guggenberger, 1933; Brown. 

 1944; Sturgis, 1947). 



The activity of the several segments of 

 the female genital tract varies with phases 

 of the ovarian cycle and, as a consequence, 

 may alter the rate of sperm migration (see 

 Austin and Bishop, 1957). The active motil- 

 ity of both the Fallopian tube and uterus, 

 characteristic of estrus, is depressed by pro- 

 gestational conditions, although little change 

 is found immediately after ovulation (Rey- 

 nolds, 1949; Borell, Nilsson and Westman, 

 1957; Black and Asdell, 1958). Cyclic 

 changes in sperm-transport time through the 

 uterus and oviducts have been noted in the 

 cow (Warbritton, McKenzie, Berliner and 

 Andrews, 1937) and sow (du Mesnil du Buis- 

 son and Dauzier, 1955 ) . Recent work of 

 Noyes, Adams and Walton (1959) suggests 

 that estrogen enhances fertilization of rab- 

 bit ova transplanted into castrates by in- 

 creasing the efficacy of sperm transport, i.e., 

 by reducing the obstacles to sperm migra- 

 tion present in nonestrous does (Noyes, 

 1959a). 



The most spectacular development involv- 

 ing endocrine control of sperm transport 

 during the past decade has been the demon- 

 stration that oxytocin, as an important me- 

 diator of uterine activity, is essential, in 

 some cases at least, for the rapid migration 

 of sperm from the cervix to the site of fer- 



tilization (VanDemark and Moeller, 1951; 

 VanDemark and Hays, 1952; Hays and 

 VanDemark, 1951, 1953a). Excised and per- 

 fused cow uteri function as a transport sys- 

 tem so long as oxytocin is present in the per- 

 fusate. Motile sperm, artificially inseminated 

 into the cervix, are carried to the ovarian 

 end of the oviduct in as few as 2.5 minutes. 

 Even nonmotile sperm are transported 

 throughout the tract within 5 minutes. In 

 the absence of oxytocin, however, sperm mi- 

 gration does not occur; in fact, the cells do 

 not even enter the fundus. Oxytocin is also 

 apparently released during natural and ar- 

 tifical insemination of the cow (Hays and 

 VanDemark, 1951, 1953b). and its admin- 

 istration, during mating, augments uter- 

 ine contractility (Hays and VanDemark, 

 1953a ) . Oxytocin may have a general role 

 in the uterine responses to mating and rapid 

 transport of spermatozoa through the geni- 

 tal tracts of some other animals as well 

 (Harris, 1951; Cross, 1958), although it is 

 to be noted that coitus is claimed to abolish 

 temporarily uterine contractions in women 

 (Bickers and Main, 1941). 



C. CRITICAL REGIONS OF SPERM TRANSPORT 



The unrestricted passage of sperm, which 

 is apparently characteristic of the heifer, is 

 not, however, exhibited by all mammals. The 

 cervix, the uterotubal junction, and, to a 

 lesser degree, the isthmus of the Fallopian 

 tube can each constitute an obstacle to free 

 sperm transport. In these regions, active 

 sperm motility may then assume some sig- 

 nificance as a means of migration. In the 

 rabbit only 1 sperm in about 50,000 reaches 

 the site of fertilization; in the ewe and rat, 

 the proportion is even smaller (Braden, 

 1953). According to Braden, of the total 

 number of sperm deposited in the rabbit 

 vagina during a normal insemination (about 

 60 X 10" cells), the proportions transmitted 

 are roughly as follows: approximately 1 out 

 of 40 traverses the cervix ; of these, one-third 

 reach the uterotubal junction; 1 out of 160 

 passes the uterotubal junction and enters 

 the Fallopian tube; and of these, one-fourth 

 ultimately reach the ampulla. The distribu- 

 tion of spermatozoa throughout the rabbit 

 genital tract at various times after copula- 

 tion is presented in Figure 13.8. 



