Regulation of the phenylethanolamine N-methyltransferase gene in the adrenal gland of the spontaneous hypertensive rat

Abstract

The catecholamine epinephrine is physiologically important in cardiac function and blood pressure regulation. Phenylethanolamine N-methyltransferase (PNMT) is the terminal enzyme in the catecholamine biosynthetic pathway, responsible for epinephrine biosynthesis, and is primarily localized in the adrenal gland. In hypertensive rats, adrenal PNMT mRNA, protein and enzyme activity are elevated along with elevated levels of epinephrine, suggesting that increased expression of PNMT in the adrenal gland results in the increased adrenergic function associated with hypertension. Genetic mapping studies performed in hypertensive rats and humans have investigated the possibility that the PNMT gene may be a candidate gene for hypertension; their findings suggest that differences in expression in PNMT in hypertension are not attributed to polymorphisms within the PNMT gene. It is proposed that increased PNMT in hypertension is likely due to altered transcriptional regulation of the gene. The PNMT gene is highly regulated by key transcription factors including: Egr-1, Sp1, AP-2 and the glucocorticoid receptor. The aim of this study was to investigate the molecular mechanisms involved in the dysregulation of adrenal PNMT in a genetic model of hypertension, by examining expression of transcriptional regulators in the spontaneous hypertensive rat (SHR) in comparison to Wistar–Kyoto (WKY) normotensive controls. Results demonstrate changes in key transcription factors regulating PNMT expression within the SHR adrenal gland, coincident with elevated adrenal PNMT expression. This study suggests altered transcriptional regulation of PNMT is a contributing factor to altered adrenergic function in hypertension.