Abstract
Female rats were injected with 8 or 16 IU of pregnant mares serum gonadotropin (PMS) at 29 or 30 days of age. The primary effect of PMS seems to be initiation of ovarian development. On the first or second day following PMS injection 15 or 20 IU of human chorionic gonadotropin (HCG) were administered. Upon injection of HCG on the first day after PMS ovulation was induced in 100% of the animals. The ovulation was precocious since after PMS injection a normal course of preovulatory follicular development in prepuberal rats takes about 48 hours. A greater number of oocytes were ovulated in the animals which had been administered the larger PMS dose. While 56% of the animals treated with HCG on Day 1 mated 95% of those treated on Day 2 mated. Neither implantation sites nor blastocysts were found in the uteri of mated animals inected with HCG on Day 1 but 82% of the rats injected on Day 2 were found to have uterine implantation sites on the tenth day after detection of vaginal sperm. Thus after the time of ovulation and mating were advanced by 24 hours no evidence of normal pregnancy was seen. Since all the events studied were initiated by PMS injection alterations in follicular processes are believed to be associated with the absence of pregnancy. For a successful pregnancy synchronization of oocyte maturation and follicular development seems to be necessary.
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