β-Carotene Bioavailability and Conversion Efficiency Are Significantly Affected by Sex in Rats First Observation Suggesting a Possible Hormetic Regulation of Vitamin A Metabolism in Female Rats

Scope: To study the effect of variation in dietary vitamin A (VA) content on its hepatic and intestinal metabolism. Methods and Results: Adult female and male rats are fed with diets containing 400, 2300, or 9858 IU kg(-1) VA for 31-33 weeks. VA concentrations are measured in plasma and liver. Bioavailability and intestinal conversion efficiency of beta-carotene to VA are assessed by measuring postprandial plasma beta-carotene and retinyl palmitate concentrations after force-feeding rats with beta-carotene. Expression of genes involved in VA metabolism, together with concentrations of RBP4, BCO1, and SR-BI proteins, are measured in the intestine and liver of female rats. Plasma retinol concentrations are lower and hepatic free retinol concentrations are higher in females than in males. There is no effect of dietary VA content on beta-carotene bioavailability and its conversion efficiency, but bioavailability is higher and conversion efficiency is lower in females than in males. The expression of most genes exhibited a U-shaped dose response curve depending on VA intake. Conclusions: beta-Carotene bioavailability and conversion efficiency to VA are affected by the sex of rats. Results of gene expression suggest a hormetic regulation of VA metabolism in female rats.