Hepatic Protein Synthetic Activity in Vivo after Ethanol Administration

Hepatic protein synthetic activity in vivo was measured by the incorporation of [ 3 H]puromycin into elongating nascent polypeptides of rat liver to form peptidyl‐[ 3 H]puromycin. Our initial experiments showed that saturating doses of [ 3 H]puromycin were achieved at 3‐6 μmol/100 g body weight, and that maximum labeling of nascent polypeptides was obtained 30 min after injection of the labeled precursor. Labeled puromycin was found to be suitable for measuring changes in the status of protein synthesis, since the formation of the peptidyl‐[ 3 H]puromycin was decreased in fasted animals and was increased in rats pretreated with L‐tryptophan. [ 3 H]Puromycin incorporation into polypeptides was then measured after acute ethanol administration as well as after prolonged consumption of ethanol which was administered as part of a liquid diet for 31 days. Acute alcohol treatment caused no significant change in [ 3 H]puromycin incorporation into liver polypeptides. In rats exposed to chronic ethanol feeding, peptidyl‐[ 3 H]puromycin formation, when expressed per mg of protein, was slightly lower compared to pair‐fed controls, but was unchanged compared to chow‐fed animals. When the data were expressed per mg of DNA or per 100 g body wt, no differences in protein synthetic activity were observed among the three groups. These findings indicate that neither acute nor chronic alcohol administration significantly affects protein synthetic activity in rat liver. They further suggest that accumulation of protein in the liver, usually seen after prolonged ethanol consumption, is apparently not reflected by an alteration of hepatic protein synthesis.