862 



SPERM, OVA, AND PREGNANCY 



early pregnancy. Krehbiel (1937) found, for 

 example, in the experimentally induced de- 

 ciduomas of the rat that glycogen and lipids 

 appeared intracellularly in cells which cyto- 

 logically seemed identical with those of the 

 normal endometrium of pregnancy. 



It would be interesting to know whether 

 the same intensity of artificial stimulus 

 would induce the decidual response in the 

 uteri of a variety of animals. In the rat, for 

 example, the slightest pressure against the 

 superficial uterine epithelium, at the proper 

 time after ovulation, is sufficient to initiate 

 the decidual response. Thus a bit of lint, 

 small clumps of cells, and glass or paraffin 

 beads the approximate size of eggs effect an 

 endometrial response identical with the re- 

 sponse to the normally implanting embryo 

 (Blandau, 1949a). In this species the very 

 earliest changes in the subepithelial stroma 

 begin when the blastocyst is attached only 

 very tenuously to the uterine epithelium 

 (Fig. 14.22). From this response of the 

 endometrium, perhaps localized pressure 

 is sufficient to induce the decidual reac- 

 tion. Equally impressive is the fact that the 

 decidual response begins before there is any 

 alteration in the superficial uterine epithe- 



-r^ H^l:y.' 



'f/. 



•}^v::i/L. 





Fic. 11.22. I.MiigiiiKhii.il ^.riinn 1 hrough the anti- 

 mesometiial wall of a pregnant rat killed on the 

 5th day. The loosely attached rat blastocyst has 

 initiated the subepitheUal decidual response. There 

 is no detectable alteration in the superficial epi- 

 thelium. X 450. 



limn detectable by microscopic means. Thus, 

 any stimulus from living eggs or inert ob- 

 jects within the lumen is transmitted to the 

 underlying stroma directly through the in- 

 tact lining epithelium. Wimsatt (1944), in 

 describing the earliest phases of implanta- 

 tion in the bat, came to the conclusion that 

 the changes in the epithelium of the pocket 

 into which the blastocyst comes to rest is 

 "an expression of a localized physiologic re- 

 action of the uterus to some chemical stimu- 

 lus of unknown nature liberated by the 

 ovum, which may produce this effect by act- 

 ing locally on the epithelium or by inducing 

 a local relaxation in the uterine muscle." 



It is important to recall again that the de- 

 struction and removal of the uterine epithe- 

 lium by the trophoblastic cells of the rat 

 blastocyst do not begin until the embryo lies 

 deeply within the decidual crypt and a siz- 

 able decidual response has been elicited (Al- 

 den, 1948). Therefore, the initiation of the 

 decidual reaction and the active invasion of 

 the endometrium by the trophoblast are two 

 distinctly different phenomena separated by 

 a considerable interval of time. In the guinea 

 pig, rabbit, monkey, man, and possibly other 

 mammals, the normal decidual response is 

 not elicited until the embryo has effected the 

 removal of the sujierficial uterine epithe- 

 lium. Recently, it has been shown that there 

 is a definite species difference in the response 

 of the endometrium to glass or paraffin beads 

 inserted into the uterus of properly timed 

 females (Blandau, 1949a). In the rat, the 

 beads initiated the decidual response and 

 were implanted in a manner similar to blas- 

 tocysts. In the guinea pig, the beads did not 

 effect the removal of the uterine epithelium, 

 and only occasionally was a minimal decid- 

 ual response induced. Thus it would appear 

 for the guinea pig, at least, not only that the 

 .stimulus must be a direct one to the under- 

 lying stroma but that a certain amount of 

 tissue injury or invasion is necessary before 

 the decidual response can be initiated. 



As we suggested earlier, the initiation of 

 the decidual reaction may be the result of a 

 localized pressure exerted by the blastocyst, 

 or of the action of some chemical substance 

 secreted by the egg, which is transmitted to 

 a properly sensitized subepithelial stroma. 

 Recently, Shelesnyak (1952, 1954, 1959a, 



