[Total and contractile protein synthesis during experimental cardiac hypertrophy]

The fractional turnover rate of the total protein extracted from cardiac rat ventricles has been measured by the continuous infusion flow technique in unanesthesized animals using 3H-lysine as a marker. This turnover rate approximated 12 p. 100 per day, doubled after aortic stenosis or aortic incompetence, and reached a peak within a week after stenosis and 2 weeks after incompetence. The fractional turnover rate of actin and myosin heavy-chains has been measured by the same technique using 14C-tyrosine as a marker and preparative gel electrophoresis to isolate the protein. This turnover rate approximated 22 and 9 p. 100 per day for myosin and actin, respectively, and doubled 4 days after aortic stenosis. It is suggested that a drop in contraction efficiency triggered protein synthesis in cardiac overloading.