84 Discussion 



Harrison: Do you think they function, do they produce anything? 



Rowlands: I think it would be most difficult to prove their functional 

 activity. In two animals in which ovulation was induced very late on in 

 pregnancy the additional corpora lutea had no effect on the occurrence 

 of parturition, they regressed immediately afterwards, at the same time 

 as the corpora lutea of pregnancy. The other possibility is to observe 

 their capacity to inhibit follicular growth, but the latter recurs so 

 rapidly after normal ovulation in the guinea pig that little time is 

 available for observations to be made. Certainly, for the first 4-6 days 

 after induced ovulation and in the presence of induced corpora lutea, 

 vesicular follicles are absent. But at eight days after induced ovulation 

 they have reappeared. To this extent, there is some slight evidence that 

 they are functional. 



Krohn: Do I understand correctly that you cannot do in the guinea 

 pig what you can do in the rabbit — prolong the duration of pregnancy 

 by inducing a new set of corpora lutea ? 



Rowlands: No. In the two animals in which I induced ovulation very 

 late on in pregnancy, so that at the time of expected parturition the 

 induced corpora lutea would be in a fairly active state, they did not 

 inhibit parturition. 



Krohn : Is the corpus luteum necessary in the later stages of pregnancy 

 for the pregnancy to continue? 



Rowlands: The guinea pig is, of course, a rather peculiar animal in 

 this respect for the effect of ovariectomy on pregnancy is not quantal, 

 that is, abortion does not occur in all animals after this treatment. 

 Loeb and Hesselberg, many years ago, claimed that the corpora lutea 

 are required only for about the first 6 days after mating, but that ovari- 

 ectomy on the 3rd to 5th days of pregnancy caused some to abort on 

 about the 12th day. 



Jost: This has been studied again recently in Prof. Courrier's labora- 

 tory by Artunkal and Colonge in 1949. They found that castrating the 

 guinea pig before day 16 always produces abortion, but this abortion 

 may be avoided by progesterone. Later castration does not induce 

 abortion. So this is good evidence that the corpus luteum is neces- 

 sary during the first 16 days of pregnancy but afterwards it may be 

 suppressed. 



Huggett: Of course, if the corpus luteum is persistent the placenta 

 may not have to do quite so much. They may be supplementing each 

 other. 



T.-Duplessis: Do you have any data concerning the growth of the 

 corpora lutea during delayed pregnancy, for example in lactating rats 

 or other animals ? 



Rowlands: Not in the guinea pig but in the bank vole (Clethriomys 

 glareolus) there is a slow initial growth phase when the egg is free in the 

 tube and in the uterine lumen, which is followed by a second burst of 

 growth following the stimulus provided by implantation. 



T.-Duplessis: It would be interesting to know what happens in 

 animals like the mink where I believe you have delayed pregnancy of 

 about four or five months. 



