Hypothalamic responsiveness to oestrogen in hypothyroid rats.

When 50 iu of PMS is given at 28 days of age, ovulation occurs on day 31, in thyroidectomized rats receiving PMS at 28 days of age, ovulation appears on day 30 and 31. PMS treated thyroidectomized rats were given 0.5 mug oestrogen at 9 a.m. on day 29 or 30. Injection on day 29 increases ovulation, but the injection of day 30 has no effect. Injection of 1.0 mug oestrogen on day 29 reduces activity, however, 1.0 mug on day 30 increases ovulation. These results infer than the hypothyroid state in PMS-treated rats significantly alters hypothalamic responsiveness to oestrogen.