Thermoregulation of myocardial protein synthesis

The effect of temperature on myocardial protein synthesis was evaluated using L-[14C]phenylalanine incorporation into total protein of isolated rabbit right ventricular papillary muscles. Muscles were incubated in oxygenated Krebs-Ringer buffer containing tracer amino acid at temperatures of 25-43 degrees C or incubated without tracer at varying temperatures up to 120 min and then incubated at 37 degrees C for an additional 2 h with the tracer present for the final hour of incubation. Higher as well as lower than physiological temperatures depressed tracer amino acid incorporation. Recovery of myocardial protein synthesis from thermal injury was incomplete when the experimental temperature deviated by 6 degrees C or more from the control and exposure exceeded 60 min. In addition, tracer amino acid incorporation on reoxygenation and return to 37 degrees C in muscles exposed to anoxia at 25 degrees C did not differ from that in muscles exposed to anoxia at 37 degrees C. Specific activity of the intracellular amino acid pool was directly measured in appropriate experiments and variation of this parameter could not account for the depressed tracer amino acid incorporation. Likewise methylprednisolone (10-5 M), chloroquine phosphate (10-5 M), and glucose (15 mM), if present during hyperthemia, did not ameliorate thermal damage. It is concluded that hyperthermia as well as hypothermia can cause irreversible alterations rather than reversible inhibition of myocardial protein synthesis.