Effects of antibody to oestrogen or of ovariectomy on the incorporation of [35-S]methionine into brain protein and on gonadotrophin levels during the oestrous cycle in the rat

Abstract

The incorporation of [35S]methionine into protein of the anterior pituitary and discrete brain areas was measured following the administration of antibodies to oestrogen, ovariectomy, or adrenalectomy on the afternoon of dioestrus. The antibody to oestrogen deleted the circadian rhythms of methionine incorporation normally observed in the various brain areas together with the peaks of incorporation normally observed in the median eminence area and anterior pituitary on the evening of pro-oestrus. The peaks of incorporative activity normally observed in the preoptic area and amygdala (relative to the putamen) at 03.00 h on the day of pro-oestrus were also deleted. Administration of the antiserum on the morning of pro-oestrus failed to alter the pattern of methionine incorporation normally observed on the evening of pro-oestrus. Ovariectomy performed at 16.00 h of dioestrus blocked the preovulatory rise of luteinizing hormone (LH) (as did the antibody to oestrogen) and inhibited the peak of methionine incorporation normally observed in the anterior pituitary on the evening of pro-oestrus. However, for the peak in the median eminence to be inhibited, ovariectomy had to be performed on the morning of the preceeding oestrus. Adrenalectomy alone, or adrenalectomy with ovariectomy, performed on the afternoon of dioestrus did not affect the levels of methionine incorporation in the brain or anterior pituitary at 18.00 h on the day of pro-oestrus. Animals which had been ovariectomized and injected with 2-5 mug oestradiol benzoate on the morning of oestrus showed significantly increased levels of methionine incorporation in all the brain areas and the anterior pituitary at 18.00 h of expected pro-oestrus. The administration of antibody to oestrogen to a similar group of animals on the afternoon of expected dioestrus inhibited the rise at 18.00 h of expected pro-oestrus. The apparent discrepancy between the results obtained with ovariectomy and the antiserum appeared to be due to the ability of the antiserum to neutralize the activity of oestrogens retained by the tissues. The present results suggest that the changes in incorporation of methionine into protein in the brain and anterior pituitary are brought about by the action of endogenous oestrogen: there appears to be a steady summative effect on the median eminence throughout the oestrous cycle together with a short-lived effect occurri4g during pro-oestrus and affecting the anterior pituitary.