DIETARY VITAMIN-A MODULATES THE PROPERTIES OF RETINOIC ACID AND GLUCOCORTICOID RECEPTORS IN RAT-LIVER

Properties of retinoic acid receptors and glucocorticoid receptors of rat liver were influenced by retinol status in a nonsimilar manner. Th e binding of the retinoic acid receptors which was lowered in vitamin A-deficient animals relative to controls was restored by a single dose (100 mug) of retinoic acid; in vitamin A-overloaded animals (40-fold the control intake) the binding was greater than in controls. The bind ing of the glucocorticoid receptor was higher in vitamin A-deficient r ats than in controls and restored by retinoic acid supplementation, bu t did not differ from controls in the vitamin A-overloaded rats. The c ellular actions of glucocorticoid hormone and retinoic acid were inves tigated by assaying the activity of some related enzymes. The activity of tyrosine aminotransferase reflected glucocorticoid receptor bindin g in vitamin A-deficient and vitamin A-restored rats. The decreased ty rosine amino transferase activity observed in vitamin A-overloaded rat s could be related to the inhibition of expression of tyrosine amino t ransferase gene by retinoic acid, Alcohol dehydrogenase activity was u naffected or only slightly affected by vitamin A status. The known exi stence of glucocorticoid hormone- and retinoic acid-sensitive elements in the alcohol dehydrogenase gene could explain such observations. Fu rthermore, the changes in the binding of retinoic acid receptors and g lucocorticoid receptors were often in opposite directions. These resul ts provide new evidence for the mechanisms by which the amount of diet ary vitamin A modulates hormonal status.