Role of ovarian hormones in the regulation of protein metabolism in women: effects of menopausal status and hormone replacement therapy

Abstract

The age-related decline in fat-free mass is accelerated in women after menopause, implying that ovarian hormone deficiency may have catabolic effects on lean tissues. Because fat-free mass is largely determined by its protein content, ovarian hormones would exert control through their effects on protein balance. Thus, we examined the effect of menopausal status and hormone replacement therapy on protein turnover. Healthy, middle-aged premenopausal (n=15; 49 ± 1 yr) and postmenopausal (n=18; 53 ± 1 yr) women were studied. Premenopausal women were tested at one timepoint. Post-menopausal women were tested before and two months following treatment with oral conjugated estrogens (0.625 mg) plus medroxyprogesterone acetate (2.5 mg; HRT; n=9) or placebo (n=9). Whole body protein breakdown, oxidation and synthesis were measured under postabsorptive conditions using [13C]leucine. No differences in whole body protein breakdown, oxidation or synthesis were found between premenopausal and postmenopausal women. Protein metabolism remained similar between groups after statistical adjustment for differences in adiposity and when sub-groups (n=10) of women matched for percent body fat were compared. In postmenopausal women, no effect of HRT was found on body composition or whole body protein breakdown, synthesis or oxidation. Thus, our results suggest no detrimental effects of ovarian hormone deficiency coincident with the postmenopausal state and no beneficial effect of ovarian hormone repletion with HRT on whole body protein turnover. Grant support NIH AG 15821, AG13978, AG021602.