Abstract
The enlargement of the ovary observed during gestation in the rat is solely due to the corpora lutea attaining a much larger size than those of the normal cycle or those produced in non-pregnant animals by administration of gonadotropic substances; yet there has been little investigation of the factors regulating the size of the individual corpus luteum. We have shown 1 that the mere distension of the uterine cavity with paraffin leads to prolonged vaginal dioestrus and inhibits the involution of the corpora lutea of pregnancy even though the embryos and their placentae be removed; these corpora, however, showed histological signs of fatty degeneration and were unable to maintain the mammary glands in a fully developed condition. The hypophysis is not essential for the maintenance of the corpora lutea of gestation. 2 , 3 The administration of gonadotropic hormones produces larger corpora in the pregnant animal than in the non-pregnant. 4 Since the gonadotropic hormones lead not only to formation of new follicles and corpora lutea but also to involution of corpora already present, we have repeated and modified these experiments. Six rats received 3 injections of 50 units of A.P.L. (anterior-pituitary-like hormone of pregnancy urine) on 3 successive days at about mid-pregnancy. The animals were sacrificed 7 days later; their ovaries were found to contain very large numbers of corpora lutea, all of which were as large as normal corpora of gestation. There is, therefore, some factor in the pregnant animal which transforms experimentally-produced corpora lutea into corpora lutea of gestation, and maintains them throughout the whole period of pregnancy.
There is evidence that oestrin is produced in large quantities in the pregnant rodent. 5
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