The effect of the administration of sheep anti LHRH γ globulin (anti LHRHG) on the maintenance of pregnancy was investigated in rats. Nidation was confirmed by laparotomy on day 7 or 8 of pregnancy. In one experiment, rats were then injected iv with 1 ml anti LHRHG or normal sheep γ globulin (NSG) daily from days 7 to 11. The uteri were inspected again on day 14 of pregnancy, when it was found that complete resorption of the fetuses had occurred in the anti LHRHG treated rats, but that the fetuses were normal in the NSG treated control rats. The effect of a single injection of 1 ml of anti LHRHG on day 7, 8, 9, 10, 11, or 12 of pregnancy was also investigated. Administration on day 9 or 10 resulted in complete resorption of the fetuses by the time of the 2nd inspection on day 14, and treatment on day 8 or 11 was partially effective. However, treatment on day 7 or 12 exerted little effect on viability of the fetuses. None of the rats showed vaginal bleeding following treatment with anti LHRHG. Termination of pregnancy by anti LHRHG could be prevented by (SC) injection of 1 μg LHRH twice daily, or by 4 mg progesterone (SC) once daily, from days 9 through 12 of pregnancy. The ovaries of the rats treated with anti LHRHG from days 7 to 11 were smaller than those of the NSG treated control rats, and some of the corpora lutea underwent cystic degenerative changes. Lutein cells of the former were also smaller than those of the latter. Serum progesterone levels were reduced after a single injection of anti LHRHG on day 9 or 10, but not on day 7 or 12 of pregnancy. There was excellent agreement between the reduction of serum progesterone and fetal resorption. Serum LH levels were low on days 7 through 12 in the anti LHRHG treated as well as the NSG treated rats, and the possible suppressive effect of anti LHRHG on LH could not be revealed because of insufficient sensitivity of the radioimmunoassay method. No significant difference was observed in serum prolactin levels between the groups of rats. The results clearly indicate that LHRH, by maintaining progesterone secretion, is indispensable on days 9 and 10 of pregnancy for the maintenance of pregnancy.
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