Effect of oestradiol benzoate on corpora lutea in rats bearing pituitary autografts.

Abstract

ABSTRACT Female rats received pituitary autotransplants beneath the kidney capsule at 11 to 12 weeks of age or were hypophysectomized only at the metoestrous stage of the cycle. Subcutaneous injections of oestradiol benzoate (OB) were started 30 to 40 days following surgery in the first 3 experiments. In Experiments 1 and 2, Series 1 injections consisted of 50, 50 and 25 μg of OB given subcutaneously on days 0, 3 and 5. Series 2 injections were the same as Series 1 but given on days 16, 19 and 21. Pituitary grafts were removed from half of the rats on day 15 in Experiment 1. Ovarian weights were obtained on day 28. In Experiment 3, the dose of OB was raised to 100 μg per injection giving a total of 300 μg for each series. In Experiment 4, hypophysectomized rats without pituitary autotransplants were given Series 1 and 2 OB injections at the level of 125 μg per series. In Experiment 5, subcutaneous injections of OB were started 5 to 7 days following pituitary autotransplant. Rats were injected daily with 50 μg for 5, 10, 20, 40 and 80 days, with autopsies following 4 or 5 days after the last injection. In Experiment 6, 50 μg was injected daily in hypophysectomized rats without pituitary transplants for 5 and 20 days. The immediate effect of OB injections into rats bearing pituitary autografts was a significant (P < 0.01) increase in ovarian weight. Long term treatment (> 40 days) caused a significant (P < 0.05) decrease in ovarian weight. Short term treatment followed by a 23 or 35 day period of no treatment gave an even greater decrease in ovarian weight (P < 0.01). Hypophysectomized rats showed no effect on ovarian weights with similar OB treatments, indicating the importance of the pituitary gland in this response. Removal of the autotransplanted pituitary gland 10 days after the first series was completed, had no apparent effect on regression of the corpora lutea. There was no effect on adrenal weight in any of the experiments. It is suggested that oestrogens initiate a process which ultimately results in luteal regression in rats bearing pituitary autografts.