970 



SPERM, OVA, AND PREGNANCY 



12 



11 



10 



_ 9 



DO 



I ^ 



^ 5 



^ A 



3 



2 



1 ^ 



Normal pregnancy 

 Sheep SI ° 



Sheep S3 • 



Sheep S 2 « 



Sheep S2A x 



Additional sheep A 



I 

 A 



! 



I 



I 



-A ho 

 I 



I 

 I 



I 



I 

 I 



I 

 I 

 I 



I 



JL_L 



20 



40 



60 80 



Time (days) 



100 



120 



140 



Fig. 16.9. Concentration of gestagen in the blood of the pregnant ewe. Gestation levels 

 were determined bv the Hooker-Forbes test. (From G. M. Neher and M. X. Zarrow, J. 

 Endocrinol., 11,323,1954.) 



of the fact that castration of the rabbit 

 invariably leads to abortion whereas cas- 

 tration of the pregnant ewe does not do so 

 if the ovaries are removed during the sec- 

 ond half of pregnancy. Again the proges- 

 terone determinations were carried out on 

 untreated serum and the samples assayed 

 by the Hooker-Forbes technique using pro- 

 gesterone as a standard. An initial rise in 

 the serum gestagen level occurred soon 

 after mating and seemed to level off at a 

 concentration of 6 ixg. per ml. approxi- 

 mately the 50th day of gestation (Fig. 

 16.9). Thereafter, the concentration re- 

 mained unchanged for approximately 50 

 days, when a second rise to a level of 8 to 

 12 fj.g. occurred. These levels remained un- 

 changed until at least 30 minutes after par- 

 turition was complete. 



Castration at various times after the 

 66th day of pregnancy failed to influence 

 the concentration of circulating gestagen 

 or interfere with the pregnancy. The data 

 in Figure 16.10 show a normal concentra- 

 tion of 8 to 10 fxg. gestagen from the 114th 

 day of gestation to parturition although the 

 animal was ovariectomized the 114th day. 

 Pregnancy was normal in all castrated 



ewes and the expected drop in scrum ges- 

 tagen was observed following parturition. 



It can now be stated that the human 

 being, the monkey, the ewe, the rabbit, the 

 mouse, and probably the guinea pig (Her- 

 rick, 1928; Ford, Webster and Young, 

 1951) have met the problem of a second 

 source of progesterone supply with varying 

 degrees of success. In the ewe, placental re- 

 placement of the ovary as a source of pro- 

 gesterone can be considered as complete 

 by approximately the 66th day of preg- 

 nancy. Castration at this time will neither 

 interfere with the pregnancy nor with the 

 concentration of the hormone in the blood. 

 In the monkey, castration as early as the 

 25th day of gestation (Hartman, 1941) 

 does not interfere with pregnancy and in 

 the human being castration as early as the 

 41st day after the last menstrual period 

 may not interfere with pregnancy (Melin- 

 koff, 1950; Tulsky and Koff, 1957). One 

 may conclude, therefore, that the placenta 

 can adequately take on the role of the 

 ovary in this regard. On the other hand, 

 aspects of the situation in the human fe- 

 male are still puzzling, especially the blood 

 gestagen values; but despite this ambiguity 



