In this project we study the mechanisms underlying coordinate and selective regulation of the hormonal output from the adrenal medulla (AM). Enhanced catecholamine and enkephalin release is accompanied with changes in mRNA levels of proenkephalin A (pEK) and catecholamine biosynthetic enzymes: tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). The goal of this project was to examine: 1) nature of the extracallular and intracellular signals involved in the control of TH, PNMT and pEK mRNA levels; 2) role of transcription and post-transcriptional mechanisms in the processes; 3) whether expression of TH, PNMT, and pEK genes could be differentially regulated; 4) cis-and trans- acting factors involved in these regulations. We have used the following experimental models: 1) electrical stimulation of splanchnic nerves; 2) activation of the neural input by hypoglycemia and cold stress; 3) hypophysectomy and administration of glucocorticoids; 4) primary cultures of bovine AM cells. TH, PNMT and pEK mRNA levels were differentially regulated by neural inputs and by direct action of hormones (glucocorticoids and angiotensin) on the adrenal medullary cells. Inductions by depolarization and angiotensin were mediated by: influx Ca2+, calmodulin, and kinase C. Stimulation of adenylate cyclase, and depletion of the intracellular catecholamines were also associated with the transcriptionally mediated changes in mRNA levels. Currently we examine roles of Ca2+, kinase C, and muscarinic receptors in the regulation of TH, PNMT, and pEK genes. We also determine nature of signals mediating multilevel actions of angiotensin on AM cells demonstrated in this project: short-term regulation of catecholamines and enkephalin release, activation of TH, and the long-term regulation of gene expression. Our studies may contribute to a better understanding of mechanisms of information processing in multiple transmitter cells and the regulation of transmitter phenotype in the sympatho-adrenal system.
