Chronic ethanol consumption alters rat liver plasma membranes and potentiates release of alkaline phosphatase

The aim of this study was to investigate possible mechanisms involved in the elevation of serum alkaline phosphatase activity in alcoholics. Male Sprague-Dawley rats were pair-fed nutritionally adequate liquid diets containing ethanol as 36% of energy or an isocaloric amount of carbohydrate for 4-5 wk. Serum alkaline phosphatase activity was increased moderately but significantly. Hepatocytes isolated from ethanol-fed animals exhibited pronounced morphologic alterations of their plasma membranes by scanning electron microscopy and a reduced content of alkaline phosphatase despite an increase in total liver alkaline phosphatase content. Chronic ethanol feeding also potentiated the release of alkaline phosphatase from the cells during incubation with 50 mM ethanol. Furthermore, chronic ethanol feeding resulted in reduced recovery of alkaline phosphatase in hepatic plasma membranes isolated by sucrose gradient centrifugation but did not affect the recoveries of other plasma membrane markers (5'-nucleotidase and Na+,K+-adenosine triphosphatase) nor the subcellular distribution of alkaline phosphatase in the nuclear, mitochondrial, microsomal, and cytosolic fractions. These findings suggest that the increased serum alkaline phosphatase levels observed in response to chronic ethanol feeding may be due, at least in part, to increased lability of this plasma membrane enzyme.