Estrogenic effects of an antiestrogen, MER-25, on eating and body weight in rats.

Ethamoxytriphetol, MER-25, which acts as an estrogen antagonist on other estrogen-sensitive behaviors and in peripheral tissues, was found to be fully estrogenic with respect to eating behavior and body weight regulation. The MER-25 causes decreases in eating and weight gain that are not due to toxicity, as indicated by its failure to induce a learned aversion to saccharin and by its failure to alter spontaneous activity. Estradiol benzoate (EB) and MER-25 similarly affect eating and body weight in gonadectomized rats: Both cause a transient decrease in food intake and a permanent decrease in body weight relative to controls; the eating and body weight effects of both MER-25 and EB are attenuated by progesterone; and both MER-25 and EB affect females more than males. Because of its full estrogenicity, MER-25 fails to antagonize the effects of EB on eating and body weight while simultaneously antagonizing effects of EB on sexual behavior, the uterus, and the vagina. The results indicate that the systems mediating the effects of estrogens on eating and body weight differ biochemically from other behavioral and somatic estrogen-sensitive systems.