Vitamin A Status Regulates Hepatic Lecithin: Retinol Acyltransferase Activity in Rats

The activity of lecithin:retinol acyltransferase (LRAT) was determined in microsomes from the liver and small intestine of rats with differing vitamin A status. In animals depleted of retinol, as judged by undetectable liver vitamin A stores and low plasma retinol concentrations, hepatic LRAT activity was almost undetectable, whether assayed with retinol bound to cellular retinol-binding protein or solvent-dispersed retinol. In contrast, neither the activity of intestinal LRAT nor that of acyl-CoA:retinol acyltransferase in either liver or intestine differed from that of vitamin A-adequate rats. During the course of vitamin A depletion, liver LRAT activity fell progressively, nearly in parallel to the decrease in plasma retinol concentration. Oral repletion of vitamin A-depleted rats with 0.8 mg of retinol resulted in a very rapid restoration of plasma retinol concentration and full recovery of hepatic LRAT activity within 24 h, together with deposition of retinyl ester in the liver. These data strongly implicate LRAT activity in liver as responsible for the storage of hepatic retinyl esters. Retention of the intestine's capacity to esterify retinol during vitamin A deficiency provides a mechanism for capture of dietary vitamin A, while reduced hepatic LRAT activity may function to redirect retinol in liver from storage to other metabolic pathways.