Modulation by 6-hydroxydopamine of expression of the phenylethanolamine N-methyltransferase (PNMT) gene in the rat heart during immobilization stress.

Phenylethanolamine N-methyltransferase (PNMT) is the final enzyme in the catecholamine synthesizing cascade that converts noradrenaline (NA) to adrenaline (Adr). Both of these catecholamines are physiologically important hormones and neurotransmitters in mammals with profound influence on the activity of the cardiovascular system. Although PNMT activity and gene expression have been reported in the neonatal and also adult rat heart, little is known about the identity of the cells expressing PNMT mRNA. In this study, we have shown that besides PNMT in neuronal and intrinsic cardiac cells, this enzyme is expressed also in rat cardiomyocytes, as shown by immunofluorescence in isolated cardiomyocytes. To determine which cells in the heart more sensitively show stress-induced changes in PNMT mRNA expression, we performed chemical sympathectomy by administration of 6-hydroxydopamine (6-OHDA), which destroys catecholaminergic terminals. We determined PNMT mRNA levels in the left atria and ventricles of control and stressed rats. In the rats treated with 6-OHDA, PNMT mRNA levels were not changed under normal, physiological conditions compared to vehicle treated rats. Similar results were observed on isolated cardiomyocytes from control and 6-OHDA treated rats. However, 6-OHDA treatment prevented immobilization-induced increase in PNMT mRNA expression. The results allow us to propose that in the heart, the immobilization-induced increase in PNMT gene expression is probably not in cardiomyocytes, but in neuronal cells.