Changes in protein, RNA and DNA and rates of protein synthesis in muscle-containing tissues of the mature rat in response to ethanol feeding: a comparative study of heart, small intestine and gastrocnemius muscle.

1. The relative sensitivity of heart, small intestine and skeletal muscle to chronic ethanol feeding was investigated in mature Wistar rats fed ethanol as 36% of total energy intake; controls were fed the same diet in which ethanol was substituted by isoenergetic glucose. 2. Chronic ethanol feeding had no apparent effect on the protein, RNA and DNA contents of heart homogenates (atria and ventricles). The ratios of RNA/protein (synthetic capacity), RNA/DNA (synthetic material per nucleus) and protein/DNA (DNA-unit or apparent cell size) were also unaltered in the hearts of alcohol-fed rats. Fractional rates of cardiac protein synthesis (ks), and synthesis relative to RNA (kRNA) and DNA (kDNA) and absolute rates of protein synthesis (Vs) were unaffected by ethanol feeding. The total content of cardiac soluble proteins was unaltered by chronic ethanol feeding, but there were small and statistically significant decreases in the contents of the myofibrillar and stromal protein fractions. There were no differences in ks in any of the cardiac subcellular protein fractions. 3. In the small intestine, ethanol feeding had no statistically significant effect on either protein or RNA contents, but there was an apparent increase in RNA when expressed relative to either protein or DNA, though the DNA-unit was unaltered. There were also substantial decreases in ks, kRNA, kDNA and Vs of approximately 15-35%. 4. In the gastrocnemius, RNA contents were significantly reduced by ethanol feeding but protein and DNA contents were unaffected. Indices of the synthetic capacity and synthetic material per nucleus were also reduced, but the DNA-unit was unaltered. These observations were accompanied by approx. 15-30% reductions in ks, kRNA, kDNA and Vs in response to ethanol feeding. 5. It is concluded that various aspects of protein metabolism in the heart, small intestine and skeletal muscle are adversely affected by chronic ethanol toxicity. The characteristics and magnitude of the responses in each tissue differ. Effects in the heart may be subtle, though haemodynamic indices may ensue. The ethanol-induced alterations in the small intestine and skeletal muscle may be responsible for gastrointestinal disturbances in motility and skeletal muscle weakness, respectively.