In Vitro Work Load and Rat Heart Metabolism

Abstract The isolated working rat heart preparation was used to study the effects of well defined work loads on heart protein synthesis. The rate of protein synthesis was evaluated by measuring the incorporation rate of phenylalanine‐ 3 H into whole heart protein. Increased pressure load (afterload) accelerated the protein synthesis. A stimulatory effect was demonstrated with glucose or palmitate as substrate and with 1 or 5 times the normal rat plasma levels of all amino acids in the perfusion medium. The protein synthesis of both control and overloaded hearts was significantly accelerated with palmitate as substrate or with high levels of all amino acids. The work load effect could, thus, be obtained under conditions optimal for heart protein synthesis in vitro . In contrast to the stimulatory effect of in‐creased afterload the rate of protein synthesis was not changed when the left atrial filling pressure (preload) was increased, although the external heart work was raised several times. End systolic volume was markedly increased in pressure overloaded hearts compared to hearts perfused under control conditions or with increased preload. It is concluded that an increase in contractile tension during systole and/or an increase in the end systolic volume was a necessary requirement for the acceleration of protein synthesis.