Effectiveness of estradiol in preventing and reversing obesity induced by ovariectomy and high-caloric diet in female rats.

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Abstract
Estrogens were recently described as being most effective in restraining the food intake and body weight of female rats that face impending obesity. A corollary is that estrogens are more effective in preventing than reversing the body weight gain that accompanies ovariectomy (Ovx). Four experiments examined the effects of estradiol benzoate (EB) on food intake, body weight, ano-nasal length, and body weight to body length ratio (Lee index) of ovariectomized and intact rats maintained on control or high-fat diets, and of Ovx and intact rats that had been reduced by deprivation. Estradiol benzoate was highly effective in preventing the increase in food intake, body weight and ano-nasal growth after Ovx. It was relatively ineffective in reversing body weight gain after Ovx. When ano-nasal length was also considered, EB was effective in returning Ovx rats to an appropriate body weight for their increased ano-nasal length. Approximately 40% of the body weight gain after Ovx appears to be due to skeletal growth and the increased tissue mass necessary to maintain it. Intact rats fed a high-caloric diet did not exhibit an increased rate of ano-nasal growth, which indicates that the skeletal growth that occurs after Ovx is not simply a result of increased food intale. Estradiol benzoate was eventually effective in reducing the body weights of intact rats maintained on a high-fat diet, but it also reduced the body weights of intact control rats. The high-fat diet did not alter the amount of weight gained after Ovx. Apparently, EB modulates food intake and body weight by multiple mechanisms, one of which is by modulating skeletal growth. The nature of the effect of EB on the body weight of intact rats suggests that this effect occurs by still another mechanism.