Chronic vitamin A status and age affect the activity of liver lecithin: Retinol acyltransferase (LRAT)

Newly absorbed vitamin A (VA) is stored in the liver as esterified retinol. LRAT, a microsomal enzyme, is implicated in this process. We have shown previously that liver LRAT activity is regulated by VA status and exogenous retinoids. However, the effect of long-term VA status (chronic VA-marginal, control, or VA-supplemented diets), or of age, on liver LRAT activity is unknown. In this study, rats were fed diets (VA-marginal, control, or VA-supplemented) until they were 2, 8-10 or 18-20 mo old (9 diet-age groups, n=6 rats/group). Liver tissue was fixed for light and electron microscopy and LRAT activity was measured in liver homogenates using ³H-retinol bound to cellular retinol-binding protein, CRBP, as substrate. By 2-way ANOVA, VA status significantly affected liver LRAT activity (P<0.0001), but age did not. However, the interaction between VA status and age was highly significant (P<0.0001). For all ages, LRAT activity was low (averaging 20.2% of control, P<0.05) in VA-marginal rats and elevated (139.3% of control, P<0.05) in VA-supplemented rats. With increasing age, liver LRAT activity declined in VA-marginal rats, while it increased slightly but significantly in VA-supplemented rats. Liver LRAT activity was positively correlated with total plasma VA. Hepatic morphology changed with age and VA status. We conclude that within a range of chronic VA status that excludes VA deficiency and toxicity, there is significant regulation of liver LRAT activity which is correlated with plasma total retinol concentration.