Some effects of ovariectomy and estrogen replacement on body composition in the rat

Sprague-Dawley rats were ovariectomized (OvX) at 3 ages, day 2 (D2), week 4 (W4) and week 7 (W7); a group of OvX W7 rats were treated daily with estrogen (OB;2 micrograms for 2 or 5 weeks from 10 weeks of age). Rats were slaughtered at 4 ages, weeks 7, 9, 12 and 15, for the chemical analysis of carcass and skin. Chemical compositions were analysed as % wet weight and as component weights by two-way analysis of variance. Component weights were also analysed by allometry, regressing against nose-anal length. Ovariectomy increased overall body weight without causing obesity. The weight gain of the OvX rat was mainly a true growth response but OvX affected body proportions so that at a given body length the OvX rat had a larger skin and carcass than controls. Ovariectomy at the earliest age (D2) produced the smallest response in body weight and body length but produced the greatest fat redistribution towards the skin and away from the carcass; there was no net change in whole body fat levels following OvX. Long-term daily OB treatment increased fat reserves but slowed the growth of other body components, including the axial skeleton. Whereas OvX redistributed components between skin and carcass, OB treatment reversed this process.