Thyroxine treatment reduces the anorectic effect of estradiol in rats

In order to examine a possible interaction between thyroxine and estradiol in the control of feeding, 14 ovariectomized adult female rats were given daily injections of 9.8 micrograms/100 g of body weight of 1-thyroxine (T). Another 14 rats received 0.15 ml of saline (S) subcutaneously each day, and food intake was measured for both groups daily. After 15 days of treatment, 8 rats from each group were also given a single injection of 6 micrograms of estradiol benzoate (EB), and the remaining 6 rats of each group received peanut oil vehicle. It was found that T-treated rats showed a significantly smaller drop in food intake after EB than did S-treated rats. This thyroxine-induced decrease in responsiveness to EB did not appear due to any changes in body weight per se but may be related to effects of thyroxine on general metabolism.