synthesis of subcellular protein fractions in the rat heart in vivo in response to chronic ethanol feeding an investigation was made into the chronic effects of ethanol on the subcellular protein fractions in the hearts of young rats 80100 g body weight rats were fed a nutritionally adequate liquid diet containing ethanol as 36 of total energy controls were fed the same diet in which ethanol was substituted by isoenergetic glucose at the end of 6 weeks rats were killed and hearts were fractionated into sarcoplasmic myofibrillar and stromal protein fractions by differential solubilisation the total myofibrillar protein content was significantly reduced by chronic ethanol feeding though the contents of other fractions were relatively unaltered the fractional and absolute rates of myofibrillar protein synthesis were significantly increased but the synthesis rates of sarcoplasmic and stromal protein fractions were unaffected by ethanol feeding this suggests independent regulation of myofibrillar protein content in the ethanol exposed heart these changes may be responsible for alterations in myocardial function in alcoholic cardiomyopathy