The effect of chronic ethanol feeding on body and plasma composition and rates of skeletal muscle protein turnover in the rat.

(1) Sexually immature and mature rats were fed a nutritionally-complete liquid diet or isovolumetric quantities of the same diet in which 36% of the calories as glucose were substituted by isocaloric ethanol. (2) After 6 weeks ethanol feeding, significant reductions in body weight (approx. 15%) occurred in both groups of rats. In immature rats there were significant reductions (7-21%) in bone, gastrocnemius, liver, and skin weights. The total skeletal muscle mass was reduced by 20%. Lung and kidney weights were not significantly altered. In mature rats smaller decreases in organ weights were found, which were only significant for skeletal muscle and skin. The gastrocnemius protein content was significantly reduced in immature but not in mature rats. Plasma protein concentrations were unaltered in both groups. (3) Plasma aspartate aminotransaminase, gamma glutamyl transferase and creatine kinase activities in immature and mature rats were not significantly altered by ethanol feeding, but there were increases in plasma alkaline phosphatase activities in immature, but not in mature, rats. Plasma glucose was slightly raised by ethanol feeding in immature but not mature rats. Plasma triglycerides and insulin were unaltered in both groups of rats. (4) Protein synthesis was measured with a flooding dose of L[4(3)H]-phenylalanine. Rates of protein breakdown were calculated from the difference between synthesis and growth. Fractional and absolute rates of skeletal muscle protein synthesis were reduced by 13-30% by ethanol treatment, in immature and mature rats. Fractional rates of protein breakdown were also reduced by ethanol, by 13 and 19% in immature and mature rats, respectively.