LOCALIZATION OF PREPROENKEPHALIN MESSENGER-RNA IN RAT-HEART - SELECTIVE GENE-EXPRESSION IN LEFT-VENTRICULAR MYOCARDIUM

The enkephalins are derived from a common precursor protein known as p reproenkephalin (ppENK). Enkephalins appear to be one of the endogenou s ligands for the opiate receptors. In the rat the ventricular myocard ium contains more ppENK mRNA than any other tissue. To gain further in sight into the role of cardiac enkephalins, the regional and developme ntal distribution of ppENK mRNA was studied by Northern blotting and i n situ hybridization. In the early postnatal period, ppENK mRNA is low in atrial and ventricular myocardium. With maturation, ppENK expressi on increases threefold in left and right ventricular tissue, but not i n the atria or cardiac conductive system. Interestingly ppENK mRNA lev els are four times higher in the left than in the right chamber. Thus, to our knowledge, ppENK is the only gene exhibiting marked difference s in expression between the adult right and left ventricle. Given the left-side preference of ppENK expression, the possibility is raised th at the left ventricle is an endocrine organ that supplies the body wit h enkephalins.