Protein synthesis during systolic and diastolic cardiac overloading in rats: a comparative study.

The rate of protein synthesis in the heart of normal rats and those with either abdominal aortic stenosis (AS), aortic incompetence (AI) or both AS + AI, was measured by a continuous infusion of (3H) lysine. The total protein synthesis rate in normal animals averaged 13% per day. During bot types of hypertrophy, there was an increased incorporation of (3H) lysine into proteins without any significant change in the specific radioactivity of free lysine in the tissue. After 6 days of stenosis, the synthesis rate of total mixed RNA-free proteins of the two ventricles had increased to 24.8% per day, and returned to normal by the second week. After aortic incompetence, the average fractional rate of protein synthesis was near normal during the first week and a significant increase (up to 28% per day) was observed only after 2 to 3 weeks. Protein synthesis returned to normal by the first month. The rate of protein synthesis was normal in the final stage of cardiac overloading comparable to that obtained when both stenosis and incompetence had been combined. These results were in agreement with in vitro studies which showed a normal protein synthesis rate during the first hours of volume overloading It was hypothesised that the trigger for protein synthesis in both conditions was a decline in efficiency due to a change in the speed of shortening.