Regulation of Tyrosine Hydroxylase Gene Expression by Muscarinic Agonists in Rat Adrenal Medulla

Abstract

Tyrosine hydroxylase (TH) gene expression in the adrenal medulla is regulated by numerous stimuli via transsynaptic mechanisms. The adrenal chromaffin cell receptors that mediate this transsynaptic response remain unidentified. In this report we demonstrate that the muscarinic acetylcholine receptor agonist bethanechol stimulates the TH gene transcription rate in both innervated and denervated adrenal glands. Hence, this muscarinic response is not dependent on transsynaptic influences, suggesting that agonist occupation of adrenal chromaffin cell muscarinic receptors is sufficient to activate intracellular signaling pathways that stimulate the TH gene. When bethanechol is administered repeatedly over a 3-h interval (four injections spaced 1 h apart), TH mRNA levels are increased two-to threefold at 6 and 12 h after the initial injection of drug. It is surprising that this induction of TH mRNA does not lead to increases in TH activity or TH protein level. These results are consistent with the hypothesis that both transcriptional and posttranscriptional mechanisms must be regulated to induce TH protein and that muscarinic agonists activate only a subset of these mechanisms.

Long-term hypoxia modulates expression of key genes regulating adrenomedullary function in the late gestation ovine fetus

“…In addition to cholinergic regulation of catecholamine biosynthesis and release via nicotinic receptors, activation of muscarinic receptors potentiates nicotinic receptor-mediated catecholamine release in bovine adrenomedullary cells (5,42). Pharmacological studies support the expression of multiple muscarinic receptor subtypes in both bovine and rat adrenal medulla, while other studies using RT-PCR indicate that type 3 and 4 muscarinic receptors are expressed in the adrenal medulla (6,17,36). The coincident onset of the increase in expression of TH and PNMT with functional/structural innervation in the late-gestation sheep fetus supports a role for cholinergic mechanisms in…”

“…adrenal; ovine; catecholamine BY LATE GESTATION IN THE DEVELOPING ovine fetus, stress activates the sympathetic nervous system, eliciting the release of both norepinephrine and epinephrine. These catecholamines play an essential role in regulating fetal cardiovascular and metabolic responses to a wide variety of stresses and are fundamental in the adaptation of the neonate to the extrauterine environment postbirth (12,35,36). As observed in the adult, the adrenal medulla is the major source of both basal and stress-induced epinephrine in the circulation and contributes significantly to plasma norepinephrine concentrations in the late-gestation ovine fetus (12,25,34,35).…”

Chronic Nicotine Treatment Leads to Induction of Tyrosine Hydroxylase in Locus Ceruleus Neurons: The Role of Transcriptional Activation

“…TH protein was measured using Western analysis as described in previous publications (Bowyer et al, 1998;Piech-Dumas et al, 1999;Sterling and Tank, 2001). A representative group of the same LC supernatants used for assaying TH activity were used for measuring TH protein.…”

“…The samples were subjected to electrophoresis, transferred to nitrocellulose, and immunoblotted using rabbit antiserum specific for TH (Tank et al, 1984). The antibody-TH complexes were detected using the Amersham ECL system (Amersham Biosciences Inc., Piscataway, NJ) and autoradiography as described by Piech-Dumas et al (1999). The autoradiographic bands were quantitated by scanning the autoradiograms with a Hewlett Packard ScanJet 4C scanner with a transparency adaptor along with computer-assisted imaging analysis using NIH Image software to calculate the density units.…”

“…In most cases, increases in TH activity measured under V max conditions are indicative of changes in TH enzyme protein (Tank et al, 1986;Fossom et al, 1991;Piech-Dumas et al, 1999;. However, to verify that these increases in TH activity represented induction of TH enzyme protein, Western analysis was used to measure TH protein directly in a select number of LC supernatant samples that had been used for assaying TH activity.…”