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

In 5 experiments with a total of 162 female and 8 male Sprague-Dawley rats, ethamoxytriphetol (MER-25), which acts as an estrogen antagonist on other estrogen-sensitive behaviors and in peripheral tissues, was fully estrogenic with respect to eating behavior and body weight regulation. Dosages of MER-25 ranged from 100 mug to 125 mg/kg. MER-25 caused decreases in eating and weight gain that were 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; 2 mug) and MER-25 both caused a transient decrease in food intake and a permanent decrease in body weight relative to controls; the effects of both were attenuated by progesterone (5 mg); and both MER-25 and EB affected females morethan males. MER-25 failed 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. Results suggest that the systems mediating estrogen effects on eating and body weight are biochemically different from other behavioral and somatic estrogen-sensitive systems. (27 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).