Induction of phenylethanolamine N-methyltransferase mRNA expression by glucocorticoids in cultured bovine adrenal chromaffin cells

Fetal endocrine and metabolic adaptations to hypoxia: the role of the hypothalamic-pituitary-adrenal axis

In utero, hypoxia is a significant yet common stress that perturbs homeostasis and can occur due to preeclampsia, preterm labor, maternal smoking, heart or lung disease, obesity, and high altitude. The fetus has the extraordinary capacity to respond to stress during development. This is mediated in part by the hypothalamic-pituitary-adrenal (HPA) axis and more recently explored changes in perirenal adipose tissue (PAT) in response to hypoxia. Obvious ethical considerations limit studies of the human fetus, and fetal studies in the rodent model are limited due to size considerations and major differences in developmental landmarks. The sheep is a common model that has been used extensively to study the effects of both acute and chronic hypoxia on fetal development. In response to high-altitude-induced, moderate long-term hypoxia (LTH), both the HPA axis and PAT adapt to preserve normal fetal growth and development while allowing for responses to acute stress. Although these adaptations appear beneficial during fetal development, they may become deleterious postnatally and into adulthood. The goal of this review is to examine the role of the HPA axis in the convergence of endocrine and metabolic adaptive responses to hypoxia in the fetus.

ACTH-dependent regulation of microRNA as endogenous modulators of glucocorticoid receptor expression in the adrenal gland

MicroRNA (miR) are a subset of small RNA molecules, which posttranscriptionally modulate target gene expression. Although miR have been demonstrated to impact a number of processes during development and tumorigenesis, little is known about the expression and the role of miR in the adrenal gland. Because tight regulation of steroid synthesis is crucial for maintaining homeostasis upon stressful stimuli, here, we determined the miR expression pattern in mouse adrenal glands under baseline conditions, as well as 10, 30, and 60 min upon ACTH stimulation, using miR microarray. Changes in miR expression levels detected by array analysis were confirmed by real-time PCR and further analyzed by bioinformatic tools to identify miR that putatively target genes involved in adrenal function. After selecting miR, with a significant change in their expression level upon ACTH stimulation, four of the predefined miR (miR-96, miR-101a, miR-142-3p, and miR-433) were found to putatively target the glucocorticoid receptor [nuclear receptor subfamily 3, group C, member 1 (Nr3c1)]. Nr3c1 expression levels were elevated 10 min after ACTH stimulation but decreased after 60 min in comparison with baseline conditions. Modified Nr3c1-3'-untranslated region constructs were further tested by in vitro luciferase assays. Thereby, we could confirm that miR96, miR101a, miR142-3p, and miR433 target the Nr3c1-3'-untranslated region and result in a 20-40% repression of it. Taken together, ACTH stimulation could be demonstrated to acutely influence adrenal miR expression pattern in vivo; thus, potentially modulating adrenal response to acute stressors.

Effects of short-term nocturnal cortisol replacement on cognitive function and quality of life in patients with primary or secondary adrenal insufficiency: a pilot study

Cortisol replacement in patients with adrenal insufficiency usually consists of hydrocortisone (HC) given orally during day time. Due to the short half-life of hydrocortisone, cortisol levels between midnight and early morning are very low in contrast to the physiological rise of cortisol serum levels during this time. We investigated whether short-term cortisol replacement during the night improves cognitive function and well-being in these patients. Fourteen patients with adrenal insufficiency were put on HC infusion between midnight and 8 a.m. They subsequently underwent neurocognitive testing to measure intellectual functioning, concentration, memory and fine motor skills. Quality of life and mood were also evaluated. All tests were repeated after 2-4 weeks during usual oral glucocorticoid replacement therapy. Blood samples were taken for cortisol, epinephrine and norepinephrine measurement. With the exception of the digit symbol test with better scoring in the oral group (p = 0.005) there were no significant differences in neurocognitive testing, vegetative functions and quality of life on the two occasions. However, a higher cortisol level was associated with a worse performance in short-term memory. Plasma epinephrine concentration was subnormal in both groups, but increased only after intravenous hydrocortisone replacement. Mimicking the physiological rise in cortisol secretion during the night in this pilot study did neither significantly affect quality of life nor cognitive performance and vegetative functions. There was no improvement in general well being. Hydrocortisone infusion during night time might improve adrenomedullary reserve in patients with adrenal insufficiency.

Changes of dopamine content and cell proliferation by dexamethsone via pituitary adenylate cyclase-activating polypeptide in PC12 cell

Pituitary adenylate cyclase-activating polypeptide (PACAP) is an endogenous neuropeptide observed in adrenal gland and sympathetic ganglia to regulate catecholamine synthesis and release. Both PACAP and glucocorticoid showed the activity to elevate catecholamine level through the stimulation of biosynthesis. However, the relationship of glucocorticoid and PACAP for this action is still unclear. Thus, alterations of gene expression, dopamine (DA) content, and cell proliferation in rat pheochromocytoma PC12 cells are employed as indicators to clarify this relationship in the present study. From the analysis of RT-PCR, the mRNA level of PACAP was observed to be raised by dexamethasone (DEX) and this action was blocked in cells treated with RU486 (mifepristone), a glucocorticoid receptor (GR) antagonist, or actinomycin D, a transcriptional inhibitor. An increase of DA content by HPLC analysis and/or cell proliferation identified by MTT assay by DEX was also observed which could be inhibited by PACAP (6-38) at concentration sufficient to block PACAP type 1 (PAC1) receptor. These results suggest that PACAP is involved in DEX-induced DA biosynthesis and cell proliferation in PC12 cells.

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

We previously communicated that long-term hypoxia (LTH) resulted in a selective reduction in plasma epinephrine following acute stress in fetal sheep. The present study tested the hypothesis that LTH selectively reduces adrenomedullary expression of phenylethanolamine-N-methyltransferase (PNMT), the rate-limiting enzyme for epinephrine synthesis. We also examined the effect of LTH on adrenomedullary nicotinic, muscarinic, and glucocorticoid receptor (GR) expression. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dGA); adrenomedullary tissue was collected from LTH and age-matched, normoxic control fetuses at 139-141 dGA. Contrary to our hypothesis, in addition to PNMT, adrenomedullary expression (mRNA, protein) of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) were reduced in the LTH fetus. Immunocytochemistry indicated that TH and DBH expression was lower throughout the medulla, while PNMT appeared to reflect a reduction in PNMT-expressing cells. Nicotinic receptor alpha 1, 2, 3, 5, 6, 7, beta 1, 2, and 4 subunits were expressed in the medulla of LTH and control fetuses. Messenger RNA for alpha 1 and 7 and beta 1 and 2 subunits was lower in LTH fetuses. Muscarinic receptors M1, M2, and M3 as well as the GR were also expressed, and no differences were noted between groups. In summary, LTH in fetal sheep has a profound effect on expression of key enzymes mediating adrenomedullary catecholamine synthesis. Further, LTH impacts nicotinic receptor subunit expression potentially altering cholinergic neurotransmission within the medulla. These findings have important implications regarding fetal cardiovascular and metabolic responses to stress in the LTH fetus.

Adrenal medulla calcium channel population is not conserved in bovine chromaffin cells in culture

During the stress response adrenal medullary chromaffin cells release catecholamines to the bloodstream. Voltage-activated calcium channels present in the cell membrane play a crucial role in this process. Although the electrophysiological and pharmacological properties of chromaffin cell calcium channels have been studied in detail, the molecular composition of these channels has not been defined yet. Another aspect that needs to be explored is the extent to which chromaffin cells in culture reflect the adrenal medulla calcium channel characteristics. In this sense, it has been described that catecholamine release in the intact adrenal gland recruits different calcium channels than those recruited during secretion from cultured chromaffin cells. Additionally, recent electrophysiological studies show that chromaffin cells in culture differ from those located in the intact adrenal medulla in the contribution of several calcium channel types to the whole cell current. However there is not yet any study that compares the population of calcium channels in chromaffin cells with that one present in the adrenal medulla. In order to gain some insight into the roles that calcium channels might play in the adrenal medullary cells we have analyzed the alpha1 subunit mRNA expression profile. We demonstrate that the expression pattern of voltage-dependent calcium channels in cultured bovine chromaffin cells markedly differs from that found in the native adrenal medulla and that glucocorticoids are only partially involved in those differences. Additionally, we show, for the first time, that the cardiac isoform of L-type calcium channel is present in both bovine adrenal medulla and cultured chromaffin cells and that its levels of expression do not vary during culture.

Production of insulin-like growth factor binding-proteins by bovine adrenomedullary cells: differential regulation by IGF-I and dexamethasone

In the present study we examined the production of insulin-like growth factor binding proteins (IGFBPs), in chromaffin cells, a model system for sympathetic neurons. Four IGFBPs of approximately 27, approximately 31, approximately 36 and a doublet of approximately 45-50 kDa, detected in Western ligand blots of conditioned medium, were identified in Western immunoblots as IGFBP-4, IGFBP-5, IGFBP-2 and IGFBP-3, respectively. In ligand blots IGFBP-3 and IGFBP-4 appeared as the most prominent species. IGF-I (1 nM) enhanced release of IGFBP-3 while dexamethasone (1 nM) diminished release of IGFBP-4. No significant proteolytic degradation of the IGFBPs was demonstrated. Cycloheximide completely attenuated release of the IGFBPs, indicating dependency on new synthesis of the proteins. These findings are consistent with autocrine modulation of the IGF system in bovine adrenomedullary chromaffin cells by IGFBPs. Furthermore, the specific stimulatory and inhibitory effects of IGF-I and dexamethasone, respectively, on release of the predominant species of IGFBP-3 and IGFBP-4, suggested that IGFBP production may be selectively modulated in a positive and negative manner.

Increased expression of adenylyl cyclase isoforms in the adrenal gland of diabetic Goto-Kakizaki rat

The spontaneously diabetic Goto-Kakizaki rat harbors the same defects expressed in human type 2 diabetes. It is not clear, however, whether stress factors emanating from the adrenal glands are involved in causing the diabetic state. For that reason, the authors studied gland size and expression of adenylyl cyclase isoforms in adrenal glands from Goto-Kakizaki and normal rats. Goto-Kakizaki rat adrenals were found to weigh only about half as much as those of control rats. This decrease was the result of a reduction of the cortex, especially of the zona fasciculata, whereas the medulla was unaffected. Cell density measurements showed that the total number of medullary cells in Goto-Kakizaki rats was lower than that in controls. In the cortex, the cell density did not differ between the two groups; thus, our results point to a marked hypotrophy. In the medulla of Goto-Kakizaki rats, the nuclear size was significantly increased, and there was also an overexpression of adenylyl cyclase 1, 2, 4, 6, and 8 isoforms in the adrenalin-producing cells, indicating an increased functional capacity. In the cortex, despite the cortical hypotrophy, adenylyl cyclase 5 immunoreactivity was markedly increased in Goto-Kakizaki rats, especially in the zona reticularis. It is unclear whether this morphologic change in the diabetic adrenal glands together with the overexpression of different adenylyl cyclase isoforms plays a role in the pathogenesis of this diabetic state or is a genetic defect or compensatory mechanism of diabetes in this spontaneous rodent model of type 2 diabetes.

Nitric oxide plays a role in the regulation of adrenal blood flow and adrenocorticomedullary functions in the llama fetus

The hypothesis that nitric oxide plays a key role in the regulation of adrenal blood flow and plasma concentrations of cortisol and catecholamines under basal and hypoxaemic conditions in the llama fetus was tested. At 0.6-0.8 of gestation, 11 llama fetuses were surgically prepared for long-term recording under anaesthesia with vascular and amniotic catheters. Following recovery all fetuses underwent an experimental protocol based on 1 h of normoxaemia, 1 h of hypoxaemia and 1 h of recovery. In nine fetuses, the protocol occurred during fetal I.V. infusion with saline and in five fetuses during fetal I.V. treatment with the nitric oxide synthase inhibitor L-NAME. Adrenal blood flow was determined by the radiolabelled microsphere method during each of the experimental periods during saline infusion and treatment with L-NAME. Treatment with L-NAME during normoxaemia led to a marked fall in adrenal blood flow and a pronounced increase in plasma catecholamine concentrations, but it did not affect plasma ACTH or cortisol levels. In saline-infused fetuses, acute hypoxaemia elicited an increase in adrenal blood flow and in plasma ACTH, cortisol, adrenaline and noradrenaline concentrations. Treatment with L-NAME did not affect the increase in fetal plasma ACTH, but prevented the increments in adrenal blood flow and in plasma cortisol and adrenaline concentrations during hypoxaemia in the llama fetus. In contrast, L-NAME further enhanced the increase in fetal plasma noradrenaline. These data support the hypothesis that nitric oxide has important roles in the regulation of adrenal blood flow and adrenal corticomedullary functions during normoxaemia and hypoxaemia functions in the late gestation llama fetus.

Glucocorticoids decrease phenylethanolamine N-methyltransferase mRNA expression in the immature foetal sheep adrenal

This study examined the impact of a chronic physiological elevation of plasma cortisol levels on adrenal catecholamine synthetic enzyme and proenkephalin A mRNA expression in foetal sheep. Cortisol (2.5-3. 0 mg.5 ml-1.24 h-1, n=9) or saline (0.9% saline, n=6) was infused into foetal sheep for 7 days between 109 days and 116 days gestation. Foetal plasma cortisol concentrations were higher (P<0.0005) in the cortisol infused foetuses when compared with the saline infused group (43.07+/-4.13 nmol.l-1 vs 1.67+/-0.10 nmol.l-1). There were no differences, however, in the plasma ACTH levels between the two groups. Using Northern blot analysis, adrenal phenylethanolamine N-methyltransferase (PNMT) mRNA expression was found to be reduced (P<0.005) fivefold in the cortisol infused foetuses when compared with the controls, as was the relative area of the adrenal medulla which stained positively with anti-PNMT (28.1+/-2.5% vs 44.8+/-4.8%, P<0.007). No effect of cortisol infusion was observed on adrenal tyrosine hydroxylase mRNA and protein expression or proenkephalin A mRNA expression. We conclude that before birth, adrenaline synthesis may be suppressed by a novel direct, or indirect, inhibitory effect of glucocorticoids on PNMT mRNA expression.

The adrenergic stress response in fish: control of catecholamine storage and release

In fish, the catecholamine hormones adrenaline and noradrenaline are released into the circulation, from chromaffin cells, during numerous 'stressful' situations. The physiological and biochemical actions of these hormones (the efferent adrenergic response) have been the focus of numerous investigations over the past several decades. However, until recently, few studies have examined aspects involved in controlling/modulating catecholamine storage and release in fish. This review provides a detailed account of the afferent limb of the adrenergic response in fish, from the biosynthesis of catecholamines to the exocytotic release of these hormones from the chromaffin cells. The emphasis is on three particular topics: (1) catecholamine biosynthesis and storage within the chromaffin cells including the different types of chromaffin cells and their varying arrangement amongst species; (2) situations eliciting the secretion of catecholamines (e.g. hypoxia, hypercapnia, chasing); (3) cholinergic and non-cholinergic (i.e. serotonin, adrenocorticotropic hormone, angiotensin, adenosine) control of catecholamine secretion. As such, this review will demonstrate that the control of catecholamine storage and release in fish chromaffin cells is a complex processes involving regulation via numerous hormones, neurotransmitters and second messenger systems.

Exocytosis in chromaffin cells of the adrenal medulla

The chromaffin cell has been used as a model to characterize releasable components present in secretory granules and to understand the cellular mechanisms involved in catecholamine release. Recent physiological and biochemical developments have revealed that molecular mechanisms implicated in granule trafficking are conserved in all eukaryotic species: a rise in intracellular calcium triggers regulated exocytosis, and highly conserved proteins are essential elements which interact with each other to form a molecular scaffolding, ensuring the docking of granules at the plasma membrane, and perhaps membrane fusion. However, the mechanisms regulating secretion are multiple and cell specific. They operate at different steps along the life of a granule, from the time of granule biosynthesis up to the last step of exocytosis. With regard to cell specificity, noradrenaline and adrenaline chromaffin cells display different receptor and signaling characteristics that may be important to exocytosis. Characterization of regulated exocytosis in chromaffin cells provides not only fundamental knowledge of neurosecretion but is of additional importance as these cells are used for therapeutic purposes.

Adrenal 11 beta-hydroxysteroid dehydrogenase

11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) catalyzes the interconversion of cortisol (F) to inactive cortisone (E) in man (corticosterone (B) to 11-dehydrocorticosterone (A) in rodents) and plays a crucial role in regulating corticosteroid hormone action. Two isoforms of this enzyme have been characterized; a low affinity NADP(H)-dependent enzyme (11 beta-HSD1) and a high affinity NAD-dependent dehydrogenase (11 beta-HSD2). We have analysed the expression of 11 beta-HSD in the rodent and human adrenal gland and have investigated its role with respect to glucocorticoid-mediated catecholamine biosynthesis. Our studies indicated higher expression of 11 beta-HSD2 mRNA in male versus female intact mouse adrenal. Both 11 beta-HSD isoforms were detected in intact male rat adrenal homogenates. For the 11 beta-HSD1 isoform, NADPH-dependent oxo-reductase activity exceeded that of NADP-dependent dehydrogenase activity (188 versus 98 pmol/mg.protein.hr). In situ hybridisation studies indicated specific localisation of 11 beta-HSD1 mRNA to cells at the corticomedullary junction. 11 beta-HSD2 mRNA was uniformly distributed across the cortex and was low/absent in the medulla. Administration of glycyrrhizic acid in vivo (> 100 mg/kg for 4 days) resulted in inhibition of 11 beta-HSD1 mRNA and activity and a decrease in mRNA levels for the glucocorticoid-dependent enzyme, phenylethanolamine N-methyltransferase, whilst levels of the glucocorticoid-independent enzyme, tyrosine hydroxylase were unchanged. No 11 beta-HSD expression was observed in the rat phaeochromocytoma cell line, PC12 cells, nor in human normal adrenal gland or phaeochromocytoma specimens. There are marked species and sex differences in the expression of 11 beta-HSD isoforms within the adrenal. The role of 11 beta-HSD within the adrenal gland remains obscure, but at least in the rat, the expression of the reductase enzyme, 11 beta-HSD1, to the corticomedullary junction may serve to maintain high medullary glucocorticoid concentrations required for catecholamine biosynthesis.

Modulation of catecholamine storage and release by the pituitary-interrenal axis in the rainbow trout, Oncorhynchus mykiss

This study examined the effects of pituitary-interrenal hormones on catecholamine storage and release in the rainbow trout Oncorhynchus mykiss. An extract of trout pituitary elicited the release of adrenaline, but not noradrenaline, using an in situ perfusion preparation. A variety of doses of adrenocorticotropic hormone (2-2000 mU) caused the release of both catecholamines in situ which was unaffected by pre-treatment with the ganglion blocker, hexamethonium, or the serotonergic receptor antagonist, methysergide, but was abolished in calcium-free media. Intra-arterial injections of adrenocorticotrophic hormone in vivo caused an elevation of plasma adrenaline but not noradrenaline levels. Injections of cortisol in situ did not elicit catecholamine release. Trout given an intraperitoneal implant of cortisol (50 mg.kg-1 body weight) had significantly higher plasma cortisol concentrations when compared to controls after 7 days of implantation. Increases in the levels of stored catecholamines were observed in various regions of the kidney and posterior cardinal vein following 3 and 7 days of cortisol treatment. The ability of the chromaffin cells to release catecholamines in response to cholinergic stimulation was assessed in situ after 7 days of treatment. Basal (non-stimulated) adrenaline outflowing perfusate levels were greater in the cortisol-treated fish. Cortisol treatment increased the responsiveness of the catecholamine release process to low doses of the cholinoceptor agonist carbachol. Three or 7 days of cortisol treatment did not alter the in vitro activity of the enzyme phenylethanolamine-N-methyl transferase. The results of this study demonstrate that interactions within the pituitary-adrenal axis can influence both catecholamine storage and release in the rainbow trout.

The antiglucocorticoid action of mifepristone

Glucocorticoid hormones influence the physiological activity of almost all cell types in the mammal. This is accomplished via a soluble receptor that, in the presence of an appropriate steroid, modifies the activity of RNA polymerase by binding to the site where different factors assemble for the initiation of cell transcription. The development of antiglucocorticoids has permitted the molecular elucidation of a number of underlying events. Contrary to the classical view, it is now clear that the affinity, stability and activability of the glucocorticoid receptor in the presence of a steroid are cell- and/or tissue-dependent events. The antiglucocorticoid RU 38486 can even activate transcription by binding to sites distinct from those that process transactivation by the agonist. Furthermore, glucocorticoids can sometimes activate the mineralocorticoid receptor, whereas mineralocorticoids can bind the glucocorticoid receptor. Since mifepristone is devoid of adverse toxicity, it has been used for the paraclinical diagnosis of the hypothalamus-pituitary-adrenal axis in normal volunteers, subjects with disorders of the behaviour, and the treatment of Cushing's disease. However, the whole spectrum of cell-specific processes that are antagonized by RU 38486 suggests wide ranging possibilities in the eventual application of antigluco-corticoids.

Sympathoadrenal system in stress. Interaction with the hypothalamic-pituitary-adrenocortical system

Exposure of an organism to any of a variety of stressors markedly activates the sympathoadrenal and hypothalamic-pituitary-adrenocortical systems. Interactions of these major stress systems occur at several levels in the periphery and the brain. In the present study, we used sham-operated or adrenalectomized cortisol-treated conscious rats to examine glucocorticoid effects on indices of CA release, metabolism, and synthesis, and on CA biosynthetic enzyme activities and gene expression at baseline and during immobilization stress (IMO). Adrenalectomy (ADX) stimulated basal and stress-induced increments in norepinephrine release, reuptake, metabolism, turnover, and biosynthesis. Loss of adrenomedullary hormones after ADX did not appear to contribute to these increments. Cortisol treatment reversed the ADX effects on CA indices and suppressed catecholaminergic responses to IMO in intact rats. These results suggest that endogenous glucocorticoids restrain responses of catecholamine turnover, synthesis, release, reuptake, and metabolism during stress. In contrast, in intact rats, continuous administration of cortisol lasting for 7 days exaggerated the IMO-induced increases in plasma CA levels. Inhibition of DOPA conversion to dopamine elevated plasma DOPA levels in chronically cortisol-treated stressed rats compared to saline-treated ones, suggesting a cortisol-induced increase in tyrosine hydroxylation. Stress increases TH and PNMT activities and mRNA levels in the adrenal medulla. Hypophysectomy reduced adrenal PNMT but not TH mRNA levels in control and IMO rats. Pretreatment of hypophysectomized animals with ACTH fully restored the control and IMO-induced adrenal PNMT mRNA levels and augmented PNMT but not TH mRNA responses in intact rats. Long-term cortisol administration to intact rats also elevated adrenal PNMT but not TH mRNA levels. The results indicate a suppressive effect of endogenous glucocorticoids and a stimulatory effect of chronically elevated glucocorticoid levels on sympathoadrenal activity during stress. The results also suggest that a nonneuronal, nonpituitary factor contributes to TH gene expression during some forms of stress, whereas pituitary-adrenocortical factors play the essential role in the regulation of PNMT gene expression.

Immunohistochemical localisation of steroidogenic enzymes and phenylethanolamine-N-methyl-transferase (PNMT) in the adrenal gland of the fetal and newborn foal

An increase in fetal adrenal cortisol output signals the onset of parturition in many animal species but, in the fetal horse, plasma concentrations of cortisol remain low for much of late pregnancy, with a rise occurring only very close to the time of birth (term 320-360 days). Immunohistochemistry was used to determine the localisation and changes in distribution of key steroidogenic enzymes for cortisol production; P450scc, P450C17 and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) in adrenal tissue from fetal and newborn horses and these findings were correlated with the appearance of immunoreactive (IR)-phenylethanolamine-N-methyl-transferase (PNMT), a cortisol-dependent enzyme. Five micron sections of adrenal tissue from fetuses at Day 100-156 (n = 5), Day 244-295 (n = 8), greater than Day 300 (n = 4) and from newborn foals (n = 6), were stained using specific antibodies and the avidin-biotin-peroxidase technique. All 3 steroidogenic enzymes were present by Day 150, but in less than 20% of the cortical cells. By late gestation the steroidogenic enzymes were present in approximately 30% of the cells, but the distribution varied. P450SCC and P450C17 predominated in cortical cells proximal to the medulla; 3 beta HSD was present throughout the cortex, but more in the zona fasciculata. In foals after birth, IR-3 beta HSD and IR-P450SCC had increased substantially throughout the adrenal cortex, and IR-P450C17 was present in most cells of the presumptive zonae fasciculata and reticularis. IR-PMNT was localised to nuclei of scattered medullary cells at the medullary-cortical interface by Day 150.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential induction of gene expression of catecholamine biosynthetic enzymes and preferential increase in norepinephrine by forskolin

We examined the effect of forskolin, an adenylate cyclase activator, on gene expression and the activities of the three enzymes specific for catecholamine biosynthesis [tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT)] and on the amounts of available catecholamines in primary cultured bovine adrenomedullary chromaffin cells. The results showed that TH was increased by 4.7 +/- 0.7-fold and 69% in mRNA and activity levels, respectively, compared with the untreated control. DBH was elevated by 3.2 +/- 0.2-fold in mRNA and 45% in activity. The increase in PNMT, on the other hand, was smaller: 1.7 +/- 0.2-fold in mRNA and 13% in activity. This relatively small increase in PNMT was reflected in the catecholamine levels in that the total epinephrine (EPI) was elevated by only 16% while norepinephrine (NE) was elevated by 99%, which caused a shift in the molar ratio of EPI to NE from 7.0 in the untreated control to 4.1 after forskolin treatment. A large portion of the elevated catecholamines was found in the medium, which represented a 10.1-fold increase for NE and a 6.4-fold increase for EPI compared with the control. Interestingly, this caused the remaining intracellular NE and EPI to be only 117 and 66% of the control, respectively. Thus, forskolin caused coordinate up-regulation of gene expression and enzyme activities of the three catecholamine-synthesizing enzymes but to different degrees, resulting in a relatively larger increase in NE than in EPI, both of which were released dramatically. This large enhancement of catecholamine release, as well as the dramatic shift in their ratio, implicates an important physiological role for cAMP in the regulation of in vivo sympathetic activities.

Effects of cAMP, glucocorticoids, and calcium on dopamine beta-hydroxylase gene expression in bovine chromaffin cells

To better understand the molecular mechanism underlying regulation of bovine dopamine beta-hydroxylase (DBH), the effects of elevated intracellular cAMP, glucocorticoids, and calcium were studied in primary cultured chromaffin cells. Elevation of intracellular cAMP by forskolin and treatment with its analog 8-bromo-cAMP caused an increase in the bovine DBH mRNA level by 3.5 +/- 0.5- and 7.8 +/- 0.9-fold, respectively, which was maximal at 6 h after the treatments. On the other hand, dexamethasone elicited no apparent change in DBH gene expression at various concentrations and time. The combined treatment with forskolin and dexamethasone resulted in the same degree of increase as that with forskolin alone. Increased intracellular calcium by the ionophore A23187 ranging from 50 to 500 nM caused DBH mRNA to decrease, which began to be observed after 6 h and was undetectable by 48 h. The results demonstrate the existence of coordinate and differential regulations among the enzymes involved in catecholamine biosynthesis in bovine adrenomedullary cells.

Brief cortisol exposure elevates adrenal phenylethanolamine N-methyltransferase after a necessary lag period

The present study, using bovine adrenal medullary cells, characterized in detail the time course of regulation of phenylethanolamine N-methyltransferase activity following brief glucocorticoid exposure. Cortisol pulses (10(-4) and 10(-5) M), as short as 15 min, increased phenylethanolamine N-methyltransferase activity measured 2 days following cortisol exposure, with a required lag period of 18 h or more. Phenylethanolamine N-methyltransferase activity was increased 2 days following brief (2 h) exposure to cortisol in concentrations that reach the medulla in vivo (10(-6) to 10(-4) M). Phenylethanolamine N-methyltransferase activity following both continuous and 2 h pulses of 10(-5) M cortisol were reduced by the glucocorticoid receptor antagonist, RU 38486. A 2 h pulse of nicotine (10(-5) M) increased phenylethanolamine N-methyltransferase activity with a lag period of at least 18 h, while combination treatment of nicotine and cortisol (10(-4) M) produced significantly higher increases in phenylethanolamine N-methyltransferase compared to either treatment alone. Therefore, this study provides novel in vitro evidence for the regulation of adrenomedullary phenylethanolamine N-methyltransferase activity, following a necessary lag period, by acute changes in both cortisol and nicotine.

Glucocorticoid induction of epinephrine synthesizing enzyme in rat skeletal muscle and insulin resistance

Rat skeletal muscle contains two enzymes which can make epinephrine: phenylethanolamine N-methyltransferase (PNMT) and nonspecific N-methyltransferase. We studied the time-course and mechanism by which the glucocorticoid dexamethasone increases muscle PNMT activity. We also examined the hypothesis that increased muscle E synthesis may contribute to glucocorticoid-induced insulin resistance. Dexamethasone (1 mg/kg s.c. for 12 d) increased muscle PNMT activity seven-fold but did not change NMT activity. Immunotitration with an anti-PNMT antibody indicated that the PNMT elevation was due to increased numbers of PNMT molecules. Dexamethasone rapidly increased PNMT activity and this elevation was largely maintained 6 d after glucocorticoid treatment stopped. Muscle epinephrine levels were transiently elevated by dexamethasone. Dexamethasone-treated rats had elevated insulin levels after a glucose load, and chronic administration of the PNMT inhibitor SKF 64139 reversed this increase. Chronic SKF 64139 improved glucose tolerance in normal rats. Dexamethasone induced muscle synthesis of the epinephrine-forming enzyme PNMT. A PNMT inhibitor lowered insulin levels in glucocorticoid-treated rats and glucose levels in untreated rats. These findings are compatible with antagonism of insulin-mediated glucose uptake by epinephrine synthesized in skeletal muscle.

Parallel up-regulation of catecholamine biosynthetic enzymes by dexamethasone in PC12 cells

We sought to investigate whether dexamethasone produces a coordinated, time-dependent effect on all enzymes in the catecholamine biosynthetic pathway in PC12 cells. The levels of mRNAs of tyrosine hydroxylase (TH), aromatic L-amino acid decarboxylase (AADC), and dopamine beta-hydroxylase (DBH) were examined at 0, 6, 12, 24, and 48 h after dexamethasone (5 microM) treatment to PC12 cells. The levels of all enzyme mRNAs steadily increased for 24 h, although the increase of AADC mRNA content was slow. The increased mRNA levels of TH and AADC were maintained at 48 h, whereas the level of DBH mRNA was sharply decreased at 48 h. The maximally induced mRNA levels were approximately 5.0-, 2.4-, and 7.0-fold higher than the control levels of TH, AADC, and DBH, respectively. The elevation of enzyme activities was detected later than the increase in levels of mRNAs. The maximal activities of TH, AADC, and DBH were reached between 48 and 72 h with 3.6-, 1.8-, and 8.0-fold increases, respectively. Low, but detectable, phenylethanolamine N-methyltransferase (PNMT) activity was observed in PC12 cells, and dexamethasone increased its activity 5.6-fold at 72 h. The PNMT mRNA was easily detected by northern blot analysis after exposure for 24 h to dexamethasone. The data suggest that, in PC12 cells, dexamethasone up-regulates all catecholamine biosynthetic enzyme genes in a parallel fashion.

Adrenal phenylethanolamine N-methyltransferase induction in relation to glucocorticoid receptor dynamics: evidence that acute exposure to high cortisol levels is sufficient to induce the enzyme

Glucocorticoids (GCs) are thought to regulate, in a permissive fashion, the basal activity of adrenal medullary phenylethanolamine N-methyltransferase (PNMT). However, it is unclear whether a large short-term increase in GC release, such as occurs during an acute stress response, may also play a role in PNMT regulation. The present study investigated how the GC influence over PNMT activity varies in relation to dynamic changes in the hormone-receptor signal. Using [3H]dexamethasone (DEX) and [3H]RU 28362 as radioligands, we have confirmed the presence of GC receptors in bovine adrenal medullary cells. A concentration-dependent decline in soluble GC receptor sites and an increase in nuclear uptake of [3H]DEX were found in response to GC levels as low as 5 x 10(-8) M. The loss of soluble sites plateaued between 5 x 10(-8) and 10(-6) M cortisol, with further losses occurring at 10(-5) and at 10(-4) M. The functional consequence of GC receptor binding was confirmed by measuring PNMT activity following 3-day exposure to cortisol. The pattern of PNMT induction was similar to that seen with GC receptor occupancy; at cortisol concentrations between 10(-8) and 10(-5) M, PNMT induction was at a plateau, with a further increase in activity at 10(-4) M. The increase in PNMT activity following 3-day exposure to low (10(-7) M) and high (5 x 10(-5), 10(-5) M) cortisol was blocked by the GC receptor antagonist RU 38486, suggesting a GC receptor-mediated event. Finally, a short (2 h) pulse of GC, which mimics the time course of physiological elevation of GC following acute stress, elevated adrenal medullary PNMT activity measured 3 days later. Therefore, our results provide novel evidence that short-term exposure of adrenal medullary cells to high cortisol levels can elevate PNMT activity.

Cardiac epinephrine synthesis. Regulation by a glucocorticoid

BACKGROUND

The heart can synthesize epinephrine. Homogenates of rat heart, which contain the enzymes phenylethanolamine N-methyltransferase (PNMT) and nonspecific N-methyltransferase (NMT), methylate norepinephrine to form epinephrine. The cardiac atrium contains primarily PNMT and the cardiac ventricle contains both PNMT and NMT.

METHODS AND RESULTS

Rats were given the glucocorticoid dexamethasone at doses ranging from 0.2 to 20 mg/kg. Twenty-four hours later, cardiac atria, ventricle, skeletal muscle, and adrenal had increases in PNMT activity to as much as 230% of baseline. NMT activity was unchanged. Longer-term treatment with 1 mg/kg dexamethasone daily for 12 days increased cardiac PNMT activity about fivefold and also increased atrial epinephrine levels. Dexamethasone did not alter ventricular epinephrine levels but increased levels of both PNMT and catechol-O-methyltransferase, the major catabolic enzyme for epinephrine. After dexamethasone treatment, greater volumes of anti-PNMT antiserum were needed to decrease PNMT enzymatic activity, indicating that dexamethasone treatment resulted in greater amounts of PNMT and did not just activate existing PNMT molecules. Denervation of the masseter muscle of rats by unilateral superior cervical ganglionectomy markedly diminished tissue norepinephrine and epinephrine levels but had no effect on masseter PNMT or NMT levels. We have previously shown that chemical sympathectomy with 6-hydroxydopamine increases cardiac PNMT levels. These findings suggest that PNMT is an extraneuronal enzyme in both cardiac and skeletal muscle.

CONCLUSIONS

Glucocorticoids have several cardiovascular effects, including increased cardiac output and blood pressure. Enhanced cardiac epinephrine synthesis may mediate some of these glucocorticoid effects.

Differential and coordinate regulation of TH and PNMT mRNAs in chromaffin cell cultures by second messenger system activation and steroid treatment

Primary cultures of chromaffin cells were prepared from bovine adrenal medullae and the levels of mRNA for tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) determined. The cells expressed moderate levels of TH mRNA and low levels of PNMT mRNA. The latter appeared to be more sensitive than TH mRNA to variations in the culture medium. The treatment of cultures with agents that activate signal transduction pathways, forskolin or phorbol esters, dramatically enhanced the expression of both mRNAs. The forskolin-induced increases in the steady-state levels of TH and PNMT mRNAs occurred rapidly and were apparent within 5 hours. These data suggest that the TH and PNMT genes can be regulated by second messengers. In contrast, dexamethasone treatment dramatically increased PNMT mRNA with no change in TH mRNA. The increase in PNMT mRNA was apparent within 6 hours of addition of the drug to the culture medium.

Coordinate and differential regulation of proenkephalin A and PNMT mRNA expression in cultured bovine adrenal chromaffin cells: responses to cAMP elevation and phorbol esters

The expression of proenkephalin A (ProEnk A) mRNA and phenylethanolamine N-methyltransferase (PNMT) mRNA in response to cAMP analogues, forskolin and phorbol esters was examined in cultures of bovine adrenal chromaffin cells. Exposure of chromaffin cells to 1 mM dibutyryl cAMP for 24 h increased significantly the levels of ProEnk A mRNA, with no significant effect on the levels of PNMT mRNA. Cells exposed to the tumor promoting phorbol esters (phorbol 12-myristate 13-acetate, phorbol 12,13-dibutyrate or 4-beta-phorbol 12,13-didecanoate) for 12 h differentially activated PNMT mRNA and ProEnk A mRNA expression. The levels of PNMT mRNA were dramatically elevated in response to low concentrations (10(-9) to 10(-8)M) of these phorbol esters, but these increases were diminished at higher concentrations (10(-7) to 10(-6) M) of the phorbol esters. These responses were synergistically potentiated by dexamethasone (1 microM), a synthetic glucocorticoid. None of these effects was seen with the biologically inactive phorbol ester, 4-alpha-phorbol 12,13-didecanoate. By contrast, the expression of ProEnk A mRNA was activated by the tumor promoting phorbol esters in a concentration-dependent manner. The results of this study demonstrate a differential stimulatory effect of second messenger mechanisms in the control of PNMT and ProEnK A mRNA expression and provide further evidence for an independent control for the enkephalin and adrenaline synthesis in these cells.

Coordinate and differential regulation of proenkephalin A and PNMT mRNA expression in cultured bovine adrenal chromaffin cells: responses to secretory stimuli

The expression of proenkephalin A (ProEnk A) mRNA and phenylethanolamine N-methyltransferase (PNMT) mRNA in response to nicotine and to a number of secretagogues was examined in cultured bovine adrenal chromaffin cells. Prolonged incubation with nicotine (10 microM) resulted in a 2-fold increase in ProEnk A mRNA but had no significant effect on the level of PNMT mRNA. Similarly, prolonged stimulation with high K+ (56 mM) induced a time-dependent elevation in the level of ProEnk A mRNA reaching 4-fold basal level after 24 h incubation. By contrast, the level of PNMT mRNA was not changed by treatment with high K+. The increase in the level of ProEnk A mRNA by high K+ was abolished by the presence of 10 microM D600, a calcium channel blocker. Unlike the effects of high K+, treatment of the cells with the sodium channel activator veratridine significantly elevated the levels of both ProEnk A and PNMT mRNA. This increase in ProEnk A and PNMT mRNA levels was however less affected by D600. Stimulation of the cells with Ba2+ (1.1 mM) also stimulated the levels of ProEnk A and PNMT mRNA and this action required the presence of extracellular Ca2+. This was in contrast to the effect of Ba2+ in stimulating catecholamine secretion, which was inhibited by Ca2+ and enhanced in Ca2(+)-free buffer. The results of the present study indicate that membrane depolarization and entry of extracellular Ca2+ play an important role on the regulation of ProEnk A and PNMT mRNAs, in addition to their well-known actions on hormone secretion. Furthermore, these results suggest that the expression of ProEnk A mRNA and PNMT mRNA are under independent regulation in response to secretory stimulation.