Abstract
It is well known that hypophysectomy interrupts pregnancy in the rat when performed during the first half of pregnancy. In such animals, the pregnancy is maintained by human chorionic gonadotrophin (HCG) substituted for pituitary luteotrophin.
This study was carried out to examine for the effect of pregnant mare's serum gonadotrophin (PMSG) on maintenance of pregnancy in the rat hypophysectomized before establishment of placenta, and the effect of estrogen on maintenance of pregnancy with estrone, since PMSG stimulates estro-gen production in the ovary.
Hormones were injected subcutaneously, once daily, following hypophysectomy through day 10 of gestation (day 0 was the day of sperm detection in the vaginal smear, in the morning). Animals were sacrificed on day 20 of gestation (in this experiment, the Wistar-Imamichi rats were employed).
No effect of maintaining pregnancy was obtained by daily injections of 5, 10 and 50 I.U. of PMSG in animals hypophysectomized on days 4 and 5 of gestation. However, when animals were hypophysectomized on days 6, 7, 8 and 9 the pregnancy was maintained in various ratios by injec-tions of 1, 5 and 10 I.U. of PMSG. In the groups hypophysectomized on days 7, 8 or 9 of gestation, the pregnancy was maintained in 88% of animals, by daily injections of 5 or 10 I.U. of PMSG, but a deleterious effect of PMSG was found, when daily injections of 10 or 20 I.U. were continued to animals hypophysectomized on the same days described above.
The daily injections of 8.0 μg. of estrone maintained the pregnancy in 50 and 57% of animals hypophysectomized on days 8 and 9 of gestation, however, no effect was obtained in animals hypophysectomized on day 7, as far as daily injections of 1.016.0 μg. of estrone were continued.
This report demonstrated that it is possible for PMSG to maintain the pregnancy in rats hypophysectomized on and after day 6 of coitus, however, it is not clear whether PMSG acts directly on the corpus luteum to secretes a certain amount of progestin.
