Inhibition of protein degradation by anoxia and ischemia in perfused rat hearts.

Abstract

Hypoxia and anoxia were induced in isolated perfused rat hearts by reduction of perfusate oxygen tension. Ischemia was produced by restricting coronary flow in hearts working against high resistance. Protein degradation was estimated from release of free phenylalanine in the presence of cycloheximide, and from dilution of the specific radioactivity of perfusate phenylalanine. Both anoxia and ischemia inhibited protein degradation as compared to unpaced or paced aerobic control hearts, respectively. The effect of ischemia was greater than that of anoxia. Estimates of net phenylalanine release, in the absence of cycloheximide, suggested that rates of protein synthesis and degradation were more nearly in balance in ischemic, than in anoxic hearts. Although insulin inhibited proteolysis in aerobic tissues, no effect of the hormone was evident in energy-poor hearts. Anoxia and ischemia appeared to affect initial steps in the degradative pathway as evidenced by inhibition of the decrease in activity of Sadenosylmethionine decarboxylase. Inhibition of proteolysis in energy-poor hearts was accompanied by decreased latency of the lysosomal enzymes, P-acetylglucosaminidase and cathepsin D. A progressive reduction in perfusate oxygen tension (hypoxia) indicated that protein degradation was reduced significantly when perfusates were gassed with 30% 02, although levels of nucleotides and creatine phosphate were normal. Anoxia led to depletion of high energy phosphates and more marked inhibition of proteolysis. Lactate and hydrogen ions, metabolites that accumulate in ischemic hearts, inhibited proteolysis in aerobic and anoxic tissues. These results indicate that inhibition of protein degradation may involve both energy-depletion and metabolite accumulation.