  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 were fed with diets containing 400, 2300, or 9858 IU/kg VA for 31-33
weeks. VA concentrations were measured in plasma and liver. Bioavailability and
intestinal conversion efficiency of $\beta$-carotene to VA were 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, were measured in the intestine and liver of female rats. Plasma
retinol concentrations were lower and hepatic free retinol concentrations were
higher in females than in males. There was no effect of dietary VA content on
$\beta$-carotene bioavailability and its conversion efficiency, but
bioavailability was higher and conversion efficiency was lower in females than
in males. The expression of most genes exhibited a U-shaped dose response curve
depending on VA intake. Main 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.

Tissues and Organs