Differential effects of retinoids and chronic ethanol consumption on membranes in rats

Liver plasma membranes (LPM) were prepared from vitamin A-deficient and -sufficient rats as well as from animals treated with retinoic acid, with or without ethanol. Although the fluorescence polarization value of LPM prepared from retinoic acid-fed animals was significantly lower than that of controls (0.201 +/- 0.008 vs. 0.254 +/- 0.005, P less than 0.001), no effect was seen with a vitamin A-deficient diet (0.259 +/- 0.005). No change in the fluorescence polarization was observed in erythrocyte ghost membranes with either vitamin A deficiency or chronic ethanol consumption. The sialic acid concentration of the membranes was significantly higher in LPM and erythrocyte ghosts obtained from vitamin A-deficient animals (37.6 +/- 1.1 vs. 29.6 +/- 0.7 nmol/mg protein for LPM, P less than 0.01, and 77.7 +/- 0.6 vs. 62.0 +/- 1.7 for erythrocyte ghosts, P less than 0.001); the LPM of retinoic acid-treated animals had the lowest values (26.9 +/- 1.6 nmol/mg protein). This sialic acid concentration of LPM was positively correlated with the fluorescence polarization (r = 0.775, P less than 0.001). Chronic ethanol feeding resulted in lower hepatic and LPM vitamin A and greater LPM fluidity with higher cholesterol esters in all diet groups (P less than 0.001). Because increased sialic acid concentration has been incriminated in the pathogenesis of tumor development, it may provide a mechanism whereby lowered hepatic vitamin A promotes carcinogenesis and retinoic acid feeding opposes this process.