Increased preproenkephalin A gene expression in the rat heart after induction of a myocardial infarction

The expression of preproenkephalin A (ppENK) gene was investigated in the rat heart, following the onset of myocardial infarction induced by ligation of the left anterior descending coronary artery. The relative abundance of ppENK mRNA and the level of enkephalins were measured by Northern blot analysis and radioimmunoassay, respectively, in the ventricles from control-unoperated, sham-operated, and operated rats. Three hours after the surgery, a comparison between rats with infarction and sham-operated rats revealed that the relative abundance of ppENK mRNA and the level of enkephalins were increased three- to four- and two- to three-fold, respectively, in the ventricles of rats with infarction. No difference was observed between rats with infarction and sham-operated rats 24 h after the surgery, or between rats with infarction compared at time intervals of 3 and 24 h following the surgery. The abundance of the ppENK mRNA in the polysomal fraction of the ventricular septum was also measured 3 h after the surgery and found to be threefold higher in rats with infarction as compared with sham-operated rats. These results indicate that the level of enkephalins rapidly increases in the ventricles of rats following myocardial infarction, and that this higher level may be ascribed to a stimulation of the local synthesis of enkephalins.