Efficiency and capacity of protein synthesis are increased in pressure overload cardiac hypertrophy

We measured the rate of protein synthesis and total RNA content in the right ventricle (RV) at day 2 and day 4 after pulmonary artery constriction to determine the contributions of changes in capacity and efficiency of in vivo protein synthesis to pressure overload (PO) cardiac hypertrophy. A significant increase in the proportion of RV weight to total heart weight was observed at day 2 and day 4 when compared with untreated controls. The rate of protein synthesis was significantly higher at day 2 post-PO (0.31 +/- 0.06 day-1 or 30 +/- 5 mg.g RV-1.day-1, means +/- SD, P less than 0.05) as well as at day 4 (0.25 +/- 0.05 day-1 or 28 +/- 9 mg.g RV-1.day-1, P less than 0.05) than for untreated rabbits (0.15 +/- 0.03 day-1 or 17 +/- 4 mg.g RV-1.day-1). RNA content was significantly higher at day 2 (1.47 +/- 0.17 mg/g RV, P less than 0.05) than in controls (1.16 +/- 0.14 mg/g RV), whereas there was a slight but nonsignificant increase at day 4 (1.36 +/- 0.21 mg/g RV, P less than 0.1). The efficiency of protein synthesis (synthesis/RNA) per gram RV was significantly increased both at day 2 (20.5 +/- 2.2 g protein.g RNA-1.day-1, P less than 0.05) and day 4 (19.8 +/- 3.5 g protein.g RNA-1.day-1, P less than 0.05) compared with control (14.6 +/- 2.3 g protein.g RNA-1.day-1). The increase in efficiency appeared to be caused by pressure overload itself based on a comparison of 0-4 day data vs. data obtained from sham animals (P less than 0.05).