Influence of female and male sex steroids on body composition in the rabbit model

Objective To study the influence on body composition of estrogen replacement therapy (ERT) in female rabbits and of replacement therapy with testosterone (TRT) in male rabbits using dual-energy X-ray absorptiometry (DEXA). Methods Cholesterol-fed female and male rabbits receiving a weight-restricted diet (100 g/day) were used. Total lean tissue mass (LTM), total body fat tissue mass (FTM) and total tissue mass (TTM) were determined by DEXA at baseline, after which the animals were gonadectomized and treated with sex steroids. Soft body composition was then determined again after 30–31 weeks of treatment. Results Relative to controls, ERT with estradiol (E2) doses of 2 and 4 mg/day significantly increased LTM ( p < 0.001), whereas E2 0.5 and 1 mg/day had a neutral effect on LTM. The change in fat mass, however, was not statistically significant between groups. In male rabbits, compared with castrated control rabbits, LTM decreased in testosterone-treated animals (by 7–12%; p < 0.001) but FTM decreased relatively more (by 66–79%; p < 0.0001). In both genders, body weight correlated with TTM as determined by DEXA (r = 0.89–0.91, p < 0.0001). Conclusion In this in vivo model of growing rabbits, estrogen replacement significantly increased LTM in female animals, whereas testosterone replacement significantly decreased FTM in males, suggesting that soft body composition of both genders is significantly affected by replacement with sex steroids. Until comparable human data are available, it is speculated that similar changes in soft body composition may occur in humans treated with sex steroids.

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