BIOLOGY OF SPERMATOZOA 



737 



l)e forced through the junction from the 

 uterine to the ovarian side in both the cow 

 and ewe (Anderson, 1928). The resistance to 

 flow, in the cow at least, is greatest during 

 estrus (Anderson, 1927; Whitelaw, 1933). 

 During this early and important period of 

 investigation, the structural aspects of the 

 uterotubal junction of a wide variety of 

 mammals were described, particularly the 

 villi and folds which ajipear to guard the 

 opening of the Fallopian tubes (Lee, 1925b; 

 Anderson, 1928). Anderson's paper should 

 be consulted for details of the comparative 

 structure of the junction in 25 species of 

 mammals and for her particularly thorough 

 discussion of this region in the sow. 



A general conclusion which arises from 

 these considerations of the uterotubal junc- 

 tion is that the structure is sufficiently com- 

 plex (Fig. 13.10) to render spurious many 

 attempts to correlate forced-fluid determina- 

 tions with sperm transport. It seems likely 

 that in a case like the cat, for example, the 

 fluid pressure applied would occlude the 

 uterotubal orifices with villi or folds, and 

 that the greater the pressure, the tighter the 

 seal; under normal conditions the junction 

 would remain more or less patent, at least 

 between muscular contractions, and allow 

 for sperm transport. 



That migration through the uterotubal 

 junction in the rat, under some circum- 

 stances, is probably accomplished by the 

 gametes themselves was indicated by the 

 ingenious investigation of Leonard and Perl- 

 man ( 1949). They injected live spermatozoa 

 of one or more species, as well as dead sperm 

 and India ink particles, into the rat uterus. 

 Spermatozoa of the rat, mouse, guinea pig, 

 and bull were injected singly, and combina- 

 tions of rat-guinea pig, rat-mouse, and rat- 

 bull sperm were introduced together. Dis- 

 tribution throughout the reproductive tract 

 was determined 1 to 14 hours later. Under 

 these conditions icf. Table 13.6) motile rat 

 si)ermatozoa freely penetrated the utero- 

 tubal junction in both estrous and diestrous 

 animals, but dead spermatozoa and inert 

 particles did not; foreign spermatozoa 

 passed through only very rarely. A similar 

 experiment on the rabbit, which also shows 

 evidence of uterotubal blockade, should 

 pro^•e rewarding. 



Fig. 13.10. Uterotubal junction of the rabbit. 

 (From D. H. Anderson, Am. J. Anat., 42, 255-305, 

 1928.) 



3. The Isthmus 



The lower segment of the oviduct consti- 

 tutes a partial obstacle to sperm migration 

 in both the rat and rabbit (Chang, 1951b; 

 Braden, 1953). In the latter, transport of 

 both sperm and eggs is slowed by a decrease 

 in muscular activity, in contrast to the move- 

 ments characteristic of the upper segment of 

 the duct (Black and Asdell, 1958) . The small 

 diameter of the lumen of the isthmus, along 

 with its kinks and extensive mucosal fold- 

 ing, may also retard sperm transport. 



In a recent extensive study to ascertain 

 the source of the fluctuations in gas pres- 

 sures during tubal insufflation of the rabbit, 

 Stavorski and Hartman (1958) demon- 

 strated that the isthmus is more important 

 than the actual uterotubal union in the de- 

 gree of resistance offered to applied pressure. 

 Sphincters were observed at both the utero- 

 tubal and tubo-ampullar junctions, but the 

 elbow-like kinks in the isthmus were found 

 to be the major source of resistance. The 

 pressures necessary to force an opening were 

 of the same order of magnitude whether a 

 uterotubal or a tubo-uterine approach was 

 employed. A suddenly applied high jiressure 



