Retinol-binding protein mRNA is induced by estrogen in the kidney but not in the liver

Vitamin A is mobilized from the liver and transported in plasma as retinol bound to retinol-binding protein (RBP). In addition to the liver, several extrahepatic tissues including the kidney have been shown to contain RBP mRNA. A study was conducted to explore the role of sex hormones in the regulation of RBP mRNA levels in the kidney compared to those in the liver. Treatment of female rats with a single dose of testosterone or chronic treatment with testosterone had only a slight effect on the steady-state level of RBP mRNA in the kidney and the liver. However, treatment of male rats with estrogen caused an increase in the steady-state level of RBP mRNA in the kidney but not in the liver. A single injection of 17 beta-estradiol, either 1.0 or 0.1 micrograms/g body weight, resulted in a rapid rise in the level of RBP mRNA in the kidney which was maximal at 3-6 h (fivefold induction) after treatment. In addition, treatment of ovariectomized female rats with estrogen also resulted in a rapid rise in the accumulated level of RBP mRNA in the kidney while having no influence in the liver. Finally, studies using the anti-estrogen drug, hydroxytamoxifen, resulted in blockage of the estrogen-related induction of RBP mRNA in the kidney, suggesting that the induction of RBP mRNA in the kidney by estrogen may be mediated by the nuclear estrogen receptor. Taken together these data suggest that the regulation of RBP mRNA, levels in the liver and kidney, at least with respect to estrogen, is different.