822 



SPERM, OVA, AND PREGNANCY 



most striking changes in the oviduct is the 

 dilation of the ampulla during the heat pe- 

 riod (Sobotta, 1895; Alden, 1942b; Burdick, 

 Whitney and Emerson, 1942). In the rat 

 several of the loops of the ampulla begin to 

 dilate between the 3rd and 4th hours after 

 the onset of heat, maximal dilation being 

 about the time of ovulation (Odor, 1948) . A 

 constriction at the distal end of the dilated 

 loop is frequently visible as a distinct 

 blanched segment a few millimeters in 

 length and in which the mucosal folds fit 

 snugly against each other. This valve-like 

 constriction is responsible for the retention 

 of the oviducal fluids and eggs for at least 

 18 to 20 hours. Nothing is known of the 

 nervous or hormonal mechanisms effecting 

 the constriction, nor how spermatozoa cope 

 with the stenosis as they proceed through 

 the oviducts to reach the ampullae where 

 sperm penetration occurs. The eggs of the 

 mouse, rat, and hamster are fertilized in the 

 dilated ampullae and I'emain there for ap- 

 proximately 20 to 30 hours after ovulation 

 (Burdick, Whitney and Emerson, 1942; 

 Odor and Blandau, 1951 ; Strauss, 1956 1 . In 

 the rabbit the freshly ovulated eggs pass 

 through the upper half of the oviduct within 

 2 hours after ovulation and come to lie at 

 the junction of the ampulla and isthmus. 

 They remain here for the next day and a 

 half (Greenwald, 1959). 



Normally sperm penetration into the eggs 

 of mammals takes place in the ampullae. 

 There are, however, several interesting ex- 

 ceptions. In ferrets, tenrecs, and shrews 

 spermatozoa somehow enter the ovarian fol- 

 licles containing the ripe eggs and penetrate 

 them before ovulation. 



Both ciliary activity and peristalsis are 

 involved in moving the eggs into the dilated 

 ampullae. Burdick, Whitney and Emerson 

 (1942) showed that ciliary action in the 

 second loop of the oviduct in the mouse is 

 sufficiently strong to rotate a whole cluster 

 of eggs. Vigorous, localized peristaltic 

 waves, spaced 12 to 16 seconds apart, 

 seemed to be more important than the cilia 

 in moving the eggs towards the entrance of 

 the isthmus. Almost identical observations 

 have been reported for the transport of eggs 

 in the ampulla of the rat (Alden, 1942b; 

 Odor, 1948). 



As the time of ovulation approaches in 

 the rat, the contractions of the dilated loops 

 of the ampulla increase in amplitude more 

 than in rate. The force of the aduterine con- 

 traction waves, measured by the rate of 

 movement of particulate matter in the lu- 

 men, greatly exceeds that of the antiperi- 

 staltic activity. The contraction waves do 

 not extend beyond the constriction at the 

 uterine end of the dilated ampulla. Clumps 

 of ovulated eggs, stained lycopodium spores, 

 or ascaris eggs were moved vigorously back- 

 wards and forwards within the lumen of the 

 tube and then forced gradually into the dis- 

 tal, most dilated loop. This vigorous ac- 

 tivity subsided rapidly after ovulation and 

 would have been missed completely if con- 

 tinuous observations had not been made. It 

 would be important to determine more ac- 

 curately the temporal relationship between 

 ovulation, the dilation of the ampulla, and 

 the changes in the pattern of muscular con- 

 tractions of this area as compared with the 

 remaining coils of the oviduct. 



The passage of ova through the isthmus 

 and intramural regions proceeds at a re- 

 markably constant rate in various animals. 

 The principal forces invoked are muscular 

 or ciliary or both. Whatever the mechanism 

 for propulsion may be, it is not necessarily 

 similar for all species nor for any particular 

 segment of the oviduct within a single ani- 

 mal (Sobotta, 1914; von ]\Iikulicz-Radecki, 

 1925; von ]\Iikulicz-Radecki and Nahm- 

 macher, 1925, 1926; Kok, 1926; Alden, 

 1942b; Burdick, Whitney and Emerson, 

 1942; Odor, 1948). 



On the basis of their studies on the be- 

 havior of the rabbit oviduct in vitro, Black 

 and Asdell (1958) suggested that the move- 

 ment of the luminal contents imparted by 

 the circular muscles is ample to account for 

 the transport of sperm and eggs through all 

 of the oviduct except the isthmus. When the 

 ova reach the isthmus they w^ait until suf- 

 ficient fluid "surges down the tube to sweep 

 them through the tubo-uterine junction" 

 (Black and Asdell, 1959). 



When the in vivo movements of oviducts 

 are studied by short interval time-lapse 

 cinematography one is impressed wdth the 

 variety of contraction patterns exhibited at 

 different times in the cycle. These observa- 

 tions re-emphasize the importance of ap- 



