OPIOID GENE-EXPRESSION IN THE DEVELOPING AND ADULT-RAT HEART

Opioid peptides are known to play a role in the function and growth of the mammalian heart. Although some information about gene expression of opioids in the heart is available, there is no data on the cellular location of opioid gene expression during development or in the adult . Using in situ hybridization and rat heart ranging from embryonic day 14 (E14) to adulthood, we have evaluated the distribution of gene exp ression for proenkephalin, proopiomelanocortin, and prodynorphin. With respect to preproenkephalin mRNA (PPE mRNA), message in the ventricle was abundant from E14 (the first time point examined) until shortly a fter birth, with a marked reduction noted on postnatal days 5, 10, and 21. Adults displayed considerable message, though less than in prepar ations of embryonic and neonatal heart. PPE mRNA was detected in epica rdial, myocardial, and endocardial cells as well as the walls of blood vessels, capillaries, and fibroblasts. Preproopiomelanocortin (POMC) mRNA was only found in adults, and was localized to the myocardium. Me ssage for preprodynorphin could not be observed in the ventricles of d eveloping or adult rats. These results are the first to define the tem poral and spatial ontogeny of opioid gene expression with regard to th e emergence of cardiac architecture. The data suggest that gene expres sion for proenkephalin is especially prevalent in embryonic and neonat al rats and may be related to the modulatory activity of the opioid gr owth factor, [Met(5)]-enkephalin, on cell proliferation and differenti ation. The role of PPE and POMC mRNA in adult rat heart requires eluci dation. (C) 1998 Wiley-Liss, Inc.