Estrus- and ovariectomy-induced body weight changes: Evidence for two estrogenic mechanisms.

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Abstract
Estrogenic body weight modulation in female rats is usually thought to result indirectly from estrogenic food intake modulation. Estrogens may influence body weight by at least 2 mechanisms, 1 of which is independent of food intake changes. When female rats were ovariectomized (Ovx) and food intake was limited to preoperative levels, the Ovx animals still gained large body weight amounts. Although Ovx rats gained more weight than controls on the same amount of food, during 33 h of food deprivation Ovx and control animals lost body weight at the same rate, which indicates that the prefasting metabolic rates of the 2 groups were generally simiilar. Examination of food deprivation recovery suggested that the weight gain rate after Ovx was very gradual. During the first 40 days after surgery, the ano-nasal lengths of Ovx rats increased twice as fast as the ano-nasal lengths of the intact rats, which suggests a mechanism for the gradual increase in body weight induced by Ovx. Intact rats'' body weights followed a regular 4-day cycle during ad lib feeding, but when the estrus-associated decrease in food intake was prevented, the cyclic body weight changes were dramatically altered. Thus estrogens appear to regulate body weight by at least 2 mechanisms: food intake modulation (cycling females) and modulation of ano-nasal growth or other metabolic processes (Ovx females).