In order to observe an early change in protein synthesis in response to a rise in cardiac work load, incorporation of leucine and lysine into cardiac protein was studied in the rat heart-lung preparation. The following results were obtained.
The incorporation of lysine into the trichloracetic acid precipitable fraction was less than that of leucine. The rate of leucine incorporation into left ventricular protein was higher (49.9 mμ/g min vs. 35.5 mμg/g min) at a high cardiac power level (31.2 g m/min) than at a low level (6.5 g m/min). A similar difference was observed in the right ventricle. Since the work level of the right ventricle is lower than that of the left, the incorporation per unit increase in cardiac power and work was larger in the right than in the left ventricle. However, the relative increase in incorporation expressed in percentage of that found at low power and work levels was of a similar magnitude between the two ventricles. The incorporation was unaffected by pretreatment with actinomycin (1 mg/kg) but was greatly inhibited by puromycin (10 mg/100 ml) or cycloheximide (25 mg/kg).
It is proposed that this relationship between the amino acid incorporation and the levels of cardiac load may be the earliest signal in the development of cardiac hypertrophy.
Heart-Lung Preparation Cardiac Work Cardiac Power Myocardium Cardiac Hypertrophy Protein Synthesis Amino Acid Incorporation Actinomycin Puromycin Cycloheximide
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