Superovulation in the Androgen-Treated Immature Rat

Treatment with PMS alone fails to induce ovulation in immature Wistar rats treated with testosterone propionate on the fourth day of postnatal life, but treatment with PMS plus HCG causes ovulation. This is additional evidence that superovulation fol lowing the injection of PMS alone involves endogenous gonadotropin release. {Endocrinology 74: 811, 1964) F rats treated with testosterone during the neonatal period characteristically exhibit precocious vaginal opening and as adults show persistent vaginal cornification, absence of ovulation and decreased ovarian weight (1). In contrast, little is known of the state of the ovary before puberty in the androgen-treated rat. Since ovulation can be readily induced in the normal immature rat, the present study was undertaken to examine the ovarian response to exogenous gonadotropin (PMS alone and PMS plus HCG) in the normal and the androgen-treated immature rat. Materials and Methods Immature rats of the Wistar colonies maintained at Oxford and at Purdue were used. Litter size was reduced within 2 days of birth to 8 in the case of the Oxford colony and to 6 for the Purdue colony. Both groups were weaned at 21 days of age. The androgen treatment consisted of a single subcutaneous injection of 1.25 mg of testosterone propionate in oil on the fourth day of life, i.e., approximately 96 hr after birth. A single injection of PMS was given subcutaneously at 30 days of age for the Oxford colony and at 24 days of age for the Purdue colony. These ages were chosen because a maximal or nearmaximal ovulatory response to PMS alone is obtained at these ages in the 2 colonies. When HCG was also given it was injected subcutaneously 56 hr after the PMS treatment. All animals were killed 72-74 hr after the PMS injection, Received November 18, 1963. 1 Locke Research Fellow of the Royal Society, Oxford. 2 X-R Fellow of the Purdue Research Foundation, Purdue. 3 Senior Post-Doctoral National Science Foundation Fellow (1962-1963), Purdue. and the tubal ova were recovered and counted as previously described (2); in addition, ovarian and uterine weights were determined in the Oxford experiment. Results The ovarian weight of the androgentreated animals was significantly lower than that of the controls at 33 days of age (Table 1). This difference was also seen in animals killed at 26 days of age; the mean body weight of both 9 normal and 9 treated animals was 46 g; the average ovarian weight of the normals was 34.4 ±1.3 mg/100 g body weight and of the androgen-treated animals 21.2 ±1.9 (p