Protein and Nucleic Acid Synthesis During the Reparative Processes Following Myocardial Infarction

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Abstract
The effect of myocardial infarction upon protein and nucleic acid synthesis of the heart was studied. Myocardial infarction was produced in dogs by ligation of branches of the anterior or posterior descending coronary artery. The rate of incorporation of glycine-2-C14 into heart muscle protein was studied over a period of six weeks. The infarcted tissue showed a rapid diminution in protein synthesis after infarction; on the third day the incorporation into the infarcted tissue rose above normal and reached a maximum on the fourth. The borderline tissue also demonstrated an early increase in protein synthesis with a maximum incorporation 48 hours after infarction. The changes in the concentration of RNA paralleled those of the incorporation of glycine-C14. The concentration of DNA increased on the second day after infarction and reached a maximum on the tenth day. Studies on the incorporation of glycine-C14 into subcellular fractions showed an early renewal of cell material in the infarcted area. Incorporation into nuclear ribosomal fraction increased first, followed by mitochondria and microsomes. The incorporation into "contractile proteins" remained subnormal. The earliest increase in nucleic acid synthesis was observed for "nucleolar RNA" (p-RNA) followed by nuclear ribosomal RNA. DNA showed an increase in incorporation 48 hours after the infarction. The studies demonstrate the rapid reaction of the heart muscle to injury and the increase in protein and nucleic acid synthesis of infarcted and borderline tissue. The first step in these reactions is the synthesis of nuclear material followed by the reconstruction of mitochondria and microsomes.