Retinol-binding protein levels are increased in association with gonadotropin levels in healthy women

Recent studies have demonstrated an association between retinol-binding protein (RBP4) and insulin resistance. Retinol-binding protein is decreased in women and elevated in polycystic ovary syndrome. However, prior studies have not investigated the relationship between RBP4, gonadal steroids, and gonadotropins in healthy women. The aim of this study was to determine the RBP4 levels in a cohort of healthy women with a range of body mass indices and glucose tolerances to investigate the relationship between RBP4, gonadotropin levels, and menopausal status. Serum RBP4 levels were measured by enzyme-linked immunosorbent assay and quantitative Western blot in 88 healthy women (aged 24-59 years) from the general community in a cross-sectional study. Retinol-binding protein was higher in postmenopausal compared with premenopausal women (26.1 ± 2.1 vs 19.3 ± 0.5 μg/mL, P = .001). In univariate analysis, RBP4 was associated with follicle-stimulating hormone (r = 0.37, P = .0004), luteinizing hormone (r = 0.3, P = .005), and sex hormone-binding globulin (r = −0.24, P = .03) and trended to significance with estradiol (P = .09) but not with free testosterone or dehydroepiandrosterone sulfate. Retinol-binding protein was also associated with insulin at 2 hours during an oral glucose tolerance test (r = 0.24, P = .03) and the area under the curve for insulin during the oral glucose tolerance test (r = 0.26, P = .02). In multivariate regression modeling, both follicle-stimulating hormone (P = .03) and luteinizing hormone (P = .04) remained significantly associated with RBP4 after controlling for estradiol, sex hormone-binding globulin, insulin area under the curve, cholesterol, triglycerides, waist-to-hip ratio, and tumor necrosis factor α. Retinol-binding protein was not associated with inflammatory markers or with carotid intima-media thickness. Therefore, RBP4 is higher in postmenopausal women and is associated with gonadotropin concentrations in healthy women.