Localization and regulation of phenylethanolamine N-methyltransferase gene expression in the heart of rats and mice during stress.

Recently we have described the existence of phenylethanolamine N-methyltransferase (PNMT) mRNA in the heart of adult rats. In this study, we report the first data on distribution of the PNMT protein in rat hearts, which follows the distribution of PNMT mRNA (high levels in the atria and low levels in ventricles). The main aim of this study was to determine the localization of the PNMT mRNA in the heart and to examine whether gene expression of this enzyme is affected by immobilization (IMO) stress in a time-dependent manner. PNMT mRNA levels were detected in all seven studied parts of the heart (atria without and with intramural ganglion cells, ventricles, and septum), with the highest levels in the left atrium and its ganglionic part. Both Southern blot and sequencing verified the specificity of PNMT detected by RT-PCR. Single IMO for 2-h increased gene expression of PNMT, as determined by both RT-PCR and Real-Time PCR in the right and left atria. Surprisingly, the ganglionic parts of the atria did not respond to stress stimulation. Peak levels of PNMT mRNA were found in the 3-h interval after the IMO terminated, and also 24 h after the first or sixth IMO. Expression of aromatic L-amino acids decarboxylase and dopamine-beta-hydroxylase has also been detected in the heart of control and stressed rats. In the atria, the effect of stress is clearly modulated by glucocorticoids, since in mice with corticotrophin-releasing hormone knocked out gene the immobilization-induced increase in the PNMT mRNA levels seen in wild-type animals was abolished. Thus, our data have shown that gene expression of the PNMT is localized, not predominantly in cardiac ganglion cells, but in a wide range in atrial cardiomyocytes. Mechanism responsible for the regulation of stress-induced increase of PNMT gene expression in cardiac atria is clearly dependent on the presence of glucocorticoids.