Protein Synthetic Activity of Heart Microsomes and Ribosomes during Left Ventricular Hypertrophy in Rabbits

Abstract

Certain aspects of cytoplasmic protein synthesis have been studied during the early stages (0 to 5 days) of left ventricular hypertrophy produced by supravalvular constriction of the ascending aorta in adult rabbits. At 5 days after constriction, cell-free protein synthesis by microsomal preparations from hypertrophied heart muscle was increased, both from free phenylalanine or leucine (50 to 130%), and from phenylalanyl-soluble RNA, both with (70 to 250%) or without (70 to 150%) polyuridylic acid as artificial messenger. Such increased activity was observed as early as 24 hr, and persisted to 5 days (the limit of the study). Sham preparations also displayed increased activity at 24 hr, which subsided by 5 days. The increased activity could be localized to the microsomal fraction: no differences were found when soluble fractions from normal, sham, and hypertrophied hearts, or from liver, were interchanged. Ribosomes from hypertrophied hearts were no more active than normal ribosomes. Increased yields of microsomal, ribosomal, and soluble RNA were found. It is suggested that the increased protein synthesis occurring in hypertrophy is localized in the microsomes, that soluble factors are not of major significance, and that an increased number of ribosomes (and microsomes) play a major role.