Stimulated Catecholamine Secretion Research Articles

Enhanced Neurotrophin Signaling Following Chronic Hypoxia Potentiates Catecholamine Release from Adrenal Chromaffin Cells

Environmental stressors, including chronic hypoxia, stimulate catecholamine secretion from adrenomedullary chromaffin cells (AMCs); however, the underlying molecular mechanisms remain unclear. Here, we investigated the role of brain‐derived neurotrophic factor (BDNF) signaling in rat AMCs exposed to chronic hypoxia. In rat adrenal glands, BDNF and its tropomyosin‐related kinase B (TrkB) receptor were highly expressed in the cortex and medulla, respectively. Exposure of AMCs to chronic hypoxia (2% O2; 48 hr) in vitro caused a significant increase in TrkB mRNA expression. A similar increase was observed in an immortalized chromaffin cell line (MAH cells); however, it was absent in MAH cells deficient in the transcription factor HIF‐2a. Activation of TrkB with a specific agonist, 7,8 dihydroxyflavone (7,8 DHF), or BDNF on chronically hypoxic (Chox) AMCs increased intracellular Ca2+ ([Ca2+]i) and quantal catecholamine release to a greater extent than normoxic (Nox; 21% O2) controls. The TrkB‐induced [Ca2+]i rise was sensitive to the tyrosine kinase inhibitor K252a and nickel, but not the Ca2+ store‐depleting agent, cyclopiazonic acid. TrkB activation also induced membrane depolarization and action potential firing that occurred with a higher frequency in CHox cells. This was accompanied by a conductance increase, and the spike discharge was inhibited by pyrazole‐3, a selective TRPC3 channel blocker. These data demonstrate that, during chronic hypoxia, enhancement of BDNF‐TrkB signaling increases membrane excitability and extracellular Ca2+ influx in chromaffin cells, which leads to a marked potentiation in catecholamine secretion. This work was funded by the Natural Sciences and Engineering Research Council. A.S. is a NSERC Post‐doctoral Fellow.

Catecholamine biosynthesis and secretion: physiological and pharmacological effects of secretin.

Pituitary adenylyl cyclase activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) augment the biosynthesis of tyrosine hydroxylase (TH). We tested whether secretin belonging to the glucagon/PACAP/VIP superfamily would increase transcription of the tyrosine hydroxylase (Th) gene and modulate catecholamine secretion. Secretin activated transcription of the endogenous Th gene and its transfected promoter (EC(50) ∼4.6 nM) in pheochromocytoma (PC12) cells. This was abolished by pre-treatment with a secretin receptor (SCTR) antagonist and by inhibition of protein kinase A (PKA), mitogen-activated protein kinase, or CREB (cAMP response element-binding protein). In agreement, secretin increased PKA activity and induced phosphorylation of CREB and binding to Th CRE, suggesting secretin signaling to transcription via a PKA-CREB pathway. Secretin stimulated catecholamine secretion (EC(50) ∼3.5μM) from PC12 cells, but this was inhibited by pre-treatment with VIP-preferring receptor (VPAC1)/PACAP-preferring receptor (PAC1) antagonists. Secretin-evoked secretion occurred without extracellular Ca(2+) and was abolished by intracellular Ca(2+) chelation. Secretin augmented phospholipase C (PLC) activity and increased inositol-1,4,5-triphosphate (IP(3)) levels in PC12 cells; PLC-β inhibition blocked secretin-induced catecholamine secretion, indicating the participation of intracellular Ca(2+) from a phospholipase pathway in secretion. Like PACAP, secretin evoked long-lasting catecholamine secretion, even after only a transient exposure. Thus, transcription is triggered by nanomolar concentrations of the peptide through SCTR, with signaling along the cAMP-PKA and extracellular-signal-regulated kinase 1/2 pathways and through CREB. By contrast, secretion is triggered only by micromolar concentrations of peptide through PAC1/VPAC receptors and by utilizing a PLC/intracellular Ca(2+) pathway.

Dual effects of nobiletin, a citrus polymethoxy flavone, on catecholamine secretion in cultured bovine adrenal medullary cells

Nobiletin, a compound of polymethoxy flavones found in citrus fruits, possesses a wide range of pharmacological activities. Here we report the effects of nobiletin on catecholamine secretion in cultured bovine adrenal medullary cells. Nobiletin (1.0-100 microM) concentration-dependently stimulated catecholamine secretion and (45)Ca(2+) influx. Its stimulatory effect of nobiletin on catecholamine secretion was abolished by deprivation of extracellular Ca(2+) and partially inhibited by specific inhibitors of voltage-dependent Ca(2+) channels and Na(+)/Ca(2+) exchangers. On the other hand, nobiletin suppressed catecholamine secretion and (22)Na(+) and (45)Ca(2+) influx induced by acetylcholine, an agonist of nicotinic acetylcholine receptors, in a concentration-dependent manner. It also inhibited catecholamine secretion, (22)Na(+) influx and/or (45)Ca(2+) influx induced by veratridine, an activator of voltage-dependent Na(+) channels, and 56 mM K(+), an activator of voltage-dependent Ca(2+) channels. In Xenopus oocytes expressing alpha3beta4 neuronal acetylcholine receptors, nobiletin directly inhibited the current evoked by acetylcholine in a concentration-dependent manner similar to that observed in catecholamine secretion. The present findings suggest that nobiletin, by itself, stimulates catecholamine secretion via activation of voltage-dependent Ca(2+) channels or Na(+)/Ca(2+) exchangers, whereas it inhibits catecholamine secretion induced by acetylcholine through the suppression of Na(+) influx and Ca(2+) influx in cultured bovine adrenal medullary cells.

Antagonistic effects of two herbs in Zuojin Wan, a traditional Chinese medicine formula, on catecholamine secretion in bovine adrenal medullary cells

In order to research the target of superior efficacy and lesser side effects, combination of herbal materials has been applied to phytotherapy for thousands of years in China and some other countries. Zuojin Wan (ZJW), a famous traditional Chinese medicine formula, is used in treating gastric diseases in China. It is composed of two herbs, Rhizoma Coptidis (RC) and Fructus Evodiae (FE) in the ratio of 6: 1(w/w). In the present study, we examined the effects of ZJW, RC, FE and active components isolated from these herbs on catecholamine (CA) secretion and intracellular calcium ([Ca(2+)](i)) in cultured bovine adrenal medullary cells. Extracts of ZJW and RC and berberine, palmatine and jatrorrhizine, components of RC, all inhibited CA secretion and rise in [Ca(2+)](i) induced by acetylcholine (ACh), veratridine (Ver) and/or 56 mM K(+). On the other hand, extract of FE, evodiamine and rutaecarpine, components of FE, stimulated CA secretion and rise in [Ca(2+)](i) induced by ACh. Furthermore, different proportions of RC and FE caused different responses in CA secretion. The present findings suggest that two herbs in ZJW have opposite effects, i.e., inhibitory effect of RC and stimulatory effect of FE, on CA secretion induced by acetylcholine in cultured bovine adrenal medullary cells.

Anti-stress effects of ginseng via down-regulation of tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH) gene expression in immobilization-stressed rats and PC12 cells

Catecholamines are among the first molecules that displayed a kind of response to prolonged or repeated stress. It is well established that long-term stress leads to the induction of catecholamine biosynthetic enzymes such as tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH) in adrenal medulla. The aim of the present study was to evaluate the effects of ginseng on TH and DBH mRNA expression. Repeated (2 h daily, 14 days) immobilization stress resulted in a significant increase of TH and DBH mRNA levels in rat adrenal medulla. However, ginseng treatment reversed the stress-induced increase of TH and DBH mRNA expression in the immobilization-stressed rats. Nicotine as a ligand of the nicotinic acetylcholine receptor (nAChR) in adrenal medulla stimulates catecholamine secretion and activates TH and DBH gene expression. Nicotine treatment increased mRNA levels of TH and DBH by 3.3- and 3.1-fold in PC12 cells. The ginseng total saponin exhibited a significant reversal in the nicotine-induced increase of TH and DBH mRNA expression, decreasing the mRNA levels of TH and DBH by 57.2% and 48.9%, respectively in PC12 cells. In conclusion, immobilization stress induced catecholamine biosynthetic enzymes gene expression, while ginseng appeared to restore homeostasis via suppression of TH and DBH gene expression. In part, the regulatory activity in the TH and DBH gene expression of ginseng may account for the anti-stress action produced by ginseng.

Enhanced cAMP production mediates the stimulatory action of pituitary adenylate cyclase activating polypeptide (PACAP) on in vitro catecholamine secretion from bovine adrenal chromaffin cells.

The 38 amino acid peptide pituitary adenylate cyclase activating polypeptide (PACAP) induced a dose dependent increase of catecholamine secretion in cultures of bovine chromaffin cells. This secretagogue activity of PACAP was strictly dependent on the presence of calcium in the culture medium. If calcium was omitted from the medium no effect of PACAP on catecholamine secretion could be detected during an incubation of 20 min. Preincubation of cells with 1 nM PACAP for 5 min facilitated the subsequent nicotine stimulated catecholamine secretion during a 20 min incubation without addition of the peptide. PACAP induced catecholamine secretion was clearly accompanied by a dose dependent increase of intracellular cAMP concentrations. The percentage of cells responding to PACAP with increased catecholamine secretion was assessed by immunocytochemistry of the transient appearance of dopamine-beta-hydroxylase, associated with the membranes of the chromaffin granules on the cell surface during the secretory process. About 70% of adrenal medullary cells responded to 100 nM PACAP with enhanced secretory activity. Though PACAP stimulated catecholamine secretion, we did not observed major effects on intracellular free calcium concentrations ([Ca2+]i) as determined with fura-2 by single cell fluorescence microscopy. In maximally 20% of the cells a rise in [Ca2+]i in response to a challenge with 500 nM PACAP was observed. Lower concentrations of PACAP were without an effect on [Ca2+]i. These data indicate that the stimulatory action of PACAP on in vitro catecholamine secretion from bovine chromaffin cells is linked to a rise of intracellular cAMP.

Metoclopramide stimulates catecholamine- and granin-derived peptide secretion from pheochromocytoma cells through activation of serotonin type 4 (5-HT4) receptors

The gastroprokinetic agent metoclopramide is known to stimulate catecholamine secretion from pheochromocytomas. The aim of the study was to investigate the mechanism of action of metoclopramide and expression of serotonin type 4 (5-HT(4)) receptors in pheochromocytoma tissues. Tissue explants, obtained from 18 pheochromocytomas including the tumor removed from a 46-year-old female patient who experienced life-threatening hypertension crisis after metoclopramide administration and 17 additional pheochromocytomas (9 benign and 8 malignant) were studied. Cultured pheochromocytoma cells derived from the patient who previously received metoclopramide were incubated with metoclopramide and various 5-HT(4) receptor ligands. In addition, total mRNAs were extracted from all the 18 tumors. Catecholamine- and granin-derived peptide concentrations were measured in pheochromocytoma cell incubation medium by HPLC and radioimmunological assays. In addition, expression of 5-HT(4) receptor mRNAs in the 18 pheochromocytomas was investigated by the use of reverse transcriptase-PCR. Metoclopramide and the 5-HT(4) receptor agonist cisapride were found to activate catecholamine- and granin-derived peptide secretions by cultured tumor cells. Metoclopramide- and cisapride-evoked catecholamine- and granin-derived peptide productions were inhibited by the 5-HT(4) receptor antagonist GR 113808. 5-HT(4) receptor mRNAs were detected in the patient's tumor and the series of 17 additional pheochromocytomas. This study shows that pheochromocytomas express functional 5-HT(4) receptors that are responsible for the stimulatory action of metoclopramide on catecholamine- and granin-derived peptide secretion. All 5-HT(4) receptor agonists must therefore be contraindicated in patients with proven or suspected pheochromocytoma.

The neurotrophic effects of PACAP in PC12 cells: control by multiple transduction pathways

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are closely related members of the secretin superfamily of neuropeptides expressed in both the brain and peripheral nervous system, and they exhibit neurotrophic and neurodevelopmental effects in vivo. Like the index member of the Trk receptor ligand family, nerve growth factor (NGF), PACAP promotes the differentiation of PC12 cells, a well-established cell culture model, to investigate neuronal differentiation, survival and function. Stimulation of catecholamine secretion and enhanced neuropeptide biosynthesis are effects exerted by PACAP at the adrenomedullary synapse in vivo and on PC12 cells in vitro through stimulation of the specific PAC1 receptor. Induction of neuritogenesis, growth arrest, and promotion of cell survival are effects of PACAP that occur in developing cerebellar, hippocampal and cortical neurons, as well as in the more tractable PC12 cell model. Study of the mechanisms through which PACAP exerts its various effects on cell growth, morphology, gene expression and survival, i.e. its actions as a neurotrophin, in PC12 cells is the subject of this review. The study of neurotrophic signalling by PACAP in PC12 cells reveals that multiple independent pathways are coordinated in the PACAP response, some activated by classical and some by novel or combinatorial signalling mechanisms.

Activin A stimulates catecholamine secretion from rat adrenal chromaffin cells: a new physiological mechanism

Activin A is a member of the transforming growth factor-beta family and has known roles in the adrenal cortex, from which activin A is secreted. We aimed to find whether activin A induces secretion of catecholamines from chromaffin cells of the adrenal medulla, which neighbours the adrenal cortex in vivo. Using carbon fibre amperometry, we were able to measure catecholamine secretion in real-time from single chromaffin cells dissociated from the rat adrenal medulla. Activin A stimulated catecholamine secretion in a rapid and dose-dependent manner from chromaffin cells. This effect was fully reversible upon washout of activin A. The minimum dose at which activin A had a maximal effect was 2 nM, with an EC50 of 1.1 nM. The degree of secretion induced by activin A (2 nM) was smaller than that due to membrane depolarization caused by an increase in the external K+ concentration from 5 to 70 mM. No response to activin A was seen when Ca2+ channels were blocked by Cd2+ (200 microM). We conclude from these findings that activin A is capable of stimulating a robust level of catecholamine secretion from adrenal chromaffin cells in a concentration-dependent manner. This occurs via the opening of voltage-gated Ca2+ channels, causing Ca2+ entry, thereby triggering exocytosis. These findings illustrate a new physiological role of activin A and a new mechanism in the control of catecholamine secretion from the adrenal medulla.

Intranasal Administration of ACTH(1-24) Stimulates Catecholamine Secretion

Previously, we reported that intranasal (IN) ACTH(1-24) administration stimulates adrenocortical steroid secretion in normal subjects. To determine the efficiency of transmucosal absorption of ACTH into the adrenal medulla, we measured serum cortisol, aldosterone, epinephrine, norepinephrine and dopamine levels after IN vs. intravenous (IV) administration of 250 microg ACTH(1-24) in 7 healthy adult men (mean age 21.7 +/- 1.2 yr; range, 21 - 24 yr). Blood was collected at 0, 30, 60 and 120 min after administration of ACTH(1-24), and the levels of adrenocortical steroids and catecholamines were measured by specific RIA and HPLC methods, respectively. There were no side effects associated with IN or IV ACTH administration. Consistent with the previous study, serum cortisol and aldosterone increased after IN administration of ACTH(1-24), peaking 30 min after administration. Sixty minutes after IN and IV administration of ACTH, epinephrine levels increased by 41.9 +/- 13.1 % and 63.3 +/- 11.8 %, respectively, and remained elevated throughout the sampling period. Thirty minutes after IN or IV administration of ACTH(1-24), plasma norepinephrine levels increased by 55.9 +/- 13.4 % and 73.7 +/- 15.0 %, respectively, peaking 30 min after ACTH(1-24) administration, and decreasing to basal levels within 60 min. Plasma dopamine levels did not change after IN administration of ACTH(1-24). Adrenocortical steroid and catecholamine levels did not increase after IN administration of saline. These results demonstrate that IN administration of ACTH(1-24) not only stimulates adrenocortical steroids, but also epinephrine and norepinephrine.

Neuropeptide-Y and Y-receptors in the autocrine-paracrine regulation of adrenal gland under physiological and pathophysiological conditions (Review)

Neuropeptide-Y (NPY) is a 36-amino acid peptide, which belongs, along with peptide YY (PYY), to the pancreatic polypeptide (PP) family. The members of this family of peptides act via G protein-coupled receptors (Rs), six subtypes of which (from Y1- to Y6-R) have been identified. NPY and PYY preferentially bind the Y1-R, Y2-R and Y5-R, while PP mainly acts via the Y4-R. Evidence has been provided that the Y3-R is selective for NPY. NPY and Y-Rs are expressed in the adrenal gland (preferentially adrenal medulla) and pheochromocytomas, where they exert various autocrine-paracrine regulatory functions. Findings indicate that NPY is co-released with catecholamines under a variety of stimuli, including splanchnic nerve and cholinergic- and nicotinic-receptor activation. NPY, mainly acting via the Y1-R, Y2-R and Y3-R, either inhibits catecholamine secretion from bovine adrenal chromaffin cells or stimulates catecholamine secretion from adrenomedullary cells of humans and rats. NPY inhibits aldosterone secretion from dispersed zona glomerulosa (ZG) cells, but this effect has probably to be considered non-specific and toxic in nature, since it is obtained only using micromolar concentrations of the peptide. In contrast, NPY appears to modulate the secretory response of dispersed rat ZG cells to their main agonists (ACTH, angiotensin-II and potassium). However, there is indication that the main effect of NPY on the ZG in rats is indirect and involves the local release of catecholamines, which in turn, acting via beta-adrenoceptors, enhance the secretion of aldosterone. The prolonged treatment with NPY is also able to enhance the growth of the rat ZG. In contrast, the effects of NPY on glucocorticoid secretion from zona fasciculata-reticularis cells are negligible and doutbful. The physiological relevance of the effects of NPY on adrenal medulla and ZG remains to be addressed by future experimental studies employing more selective and potent Y-R antagonists. In contrast, indirect evidence is available that endogenous NPY system may play an important role in the modulation of adrenal functions under paraphysiological conditions (e.g. it seems to dampen exceedingly high responses to stresses). Moreover, it has been also suggested that endogenous NPY may be involved in the regulation of blood pressure and in the pathophysiology of pheochromocytomas.

Nitric oxide donors induce calcium-mobilisation from internal stores but do not stimulate catecholamine secretion by bovine chromaffin cells in resting conditions

The potential role of nitric oxide (NO) donors and peroxynitrites on both basal catecholamine (CA) secretion and modulation of calcium levels has been investigated in primary cultures of bovine chromaffin cells. NO donors did not modulate catecholamine secretion, while peroxynitrites induced a time dose-dependent increase in basal CA secretion. Two facts may explain the lack of these compounds on basal CA secretion. NO donors induce, on the one hand, an increase in intracellular calcium levels by depletion of internal IP 3-stores from endoplasmic reticulum. On the other hand, a small calcium influx through N-type voltage-dependent calcium channels (VDCC), which seem not to be coupled to exocytosis of adrenaline and noradrenaline in chromaffin cells. Both effects, calcium-mobilisation from internal stores and calcium entry through N-type VDCC are mediated by cGMP synthesis. In contrast, peroxynitrites induce an increase in basal CA secretion by both a decrease of intracellular catecholamine content and a toxic effect on cellular membrane. All these results, taken together, could explain contradictory results in the literature on the role of NO on basal catecholamine secretion and on modulation of intracellular calcium in chromaffin cells.

Effects of galantamine, a nicotinic allosteric potentiating ligand, on nicotine-induced catecholamine release in hippocampus and nucleus accumbens of rats.

Galantamine, a drug for treatment of Alzheimer's disease, is a novel cholinergic agent with a dual mode of action that inhibits acetylcholinesterase and allosterically modulates nicotinic cholinergic receptors (nAChRs). Nicotine stimulates catecholamine secretion, inducing hippocampal norepinephrine (NE) release, and improves memory consolidation. Thus, the effect of galantamine on nicotine-induced hippocampal NE secretion was investigated. This was compared with the effect of galantamine on nicotine-induced dopamine (DA) release within the nucleus accumbens of the same rat. Nicotine (0.025-0.09 mg/kg i.v.) dose dependently increased NE and DA levels in microdialysates from the hippocampus and nucleus accumbens, respectively, of freely moving rats. Pretreatment with galantamine (3.0 mg/kg s.c.) 3 h before nicotine either potentiated NE responses to doses of nicotine that were ineffective alone (0.025-0.045 mg/kg) or significantly enhanced (0.065 mg/kg) NE responses, whereas galantamine was ineffective when administered 2 or 4 h before nicotine. In contrast to its effects on NE, galantamine did not alter accumbal DA responses to any dose of nicotine. These selective effects of galantamine on nicotine-stimulated NE secretion may reflect differences in local neural circuits that use nAChRs to modulate hippocampal NE versus accumbal DA release.

Possible Role of a Neuropeptide PACAP (Pituitary Adenylate Cyclase‐Activating Polypeptide) on Stimulus‐Secretion Coupling in Catecholamine Neuron

AbstractFor Abstract see ChemInform Abstract in Full Text.

Possible role of a neuropeptide PACAP (pituitary adenylate cyclase-activating polypeptide) on stimulus-secretion coupling in catecholamine neuron

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide first isolated from ovine hypothalamic tissue. This peptide stimulates adenylate cyclase activation. However, few details were known of the function of this peptide on stimulus-secretion coupling in neuronal cells. The authors have investigated the role of PACAP on catecholamine biosynthesis and secretion using cultured bovine adrenal chromaffin cells as a model for catecholamine-containing neurons. PACAP38, the 38-amino acid form of PACAP, increased cAMP formation in bovine adrenal chromaffin cells. In addition, PACAP38 increased [Ca2+]i associated with PI turnover and Ca2+ influx into the cells. The synthesis of catecholamine and the phosphorylation of tyrosine hydroxylase, a rate-limiting enzyme of catecholamine biosynthesis, stimulated by the maximal effective concentration of dibutyryl cAMP or a high concentration (56 mM) of K+ were further enhanced by PACAP38. Thus PACAP38 stimulated the pathway of catecholamine biosynthesis mainly by both activation of cAMP- and Ca2(+)-dependent protein kinases. On catecholamine secretion from the cells, the effect of PACAP38 was markedly potentiated by addition of ouabain, an inhibitor of Na+/K+ ATPase. This markedly potentiated secretion was greatly reduced with Na+ omitted-sucrose medium. PACAP38 increased 22Na+ influx into the cells treated with ouabain. Thus PACAP38 with ouabain stimulated catecholamine secretion by accumulation of intracellular Na+, resulting in an increase in Ca2+ influx. These results indicate that the neuropeptide PACAP has an important role in stimulus-secretion coupling in adrenal chromaffin cells.

Association of adrenal pheochromocytoma and lung pathology in inhalation studies with particulate compounds in the male F344 rat--the National Toxicology Program experience.

Systemic hypoxemia, occurring in space-occupying lung pathologies such as inflammation and neoplasms. reduces the gas exchange area and stimulates catecholamine secretion from the adrenal medulla where chronic endocrine hyperactivity may lead to hyperplasia and neoplasia. We investigated the possible correlation between nonneoplastic chronic pulmonary lesions and adrenal pheochromocytoma in 9 recent, NTP, 2-year particulate inhalation studies in male F344 rats. Re-evaluation for chronic active inflammation, interstitial fibrosis, alveolar epithelial hyperplasia, squamous metaplasia, proteinosis, and histiocytosis revealed significant associations of pheochromocytoma only with the severity of inflammation and fibrosis. Nickel oxide, cobalt sulfate, indium phosphide, talc, and nickel subsulfide studies showed chemical-related incidences of adrenal pheochromocytoma and significant (p < 0.01) associations with inflammation and fibrosis. Gallium arsenide, vanadium pentoxide, molybdenum trioxide, and nickel sulfate hexahydrate studies revealed an increased incidence and/or severity of nonneoplastic lung lesions, but no increased incidence of pheochromocytoma. Although gallium arsenide and molybdenum trioxide showed no dose-related increase in pheochromocvtoma, a significant (p < 0.01) correlation of the latter with the severity of fibrosis and inflammation occurred. In the vanadium pentoxide and nickel sulfate hexahydrate studies, no relationship between nonneoplastic lung lesions and pheochromocytoma was manifested. Our investigation assessed the strength of these various associations and supports the possible roles of 2 chronic pulmonary lesions-fibrosis and inflammation-and hypoxemia in the induction of pheochromocytoma in the F344 male rat.

Human pheochromocytomas express orexin receptor type 2 gene and display an in vitro secretory response to orexins A and B.

Orexins A and B are hypothalamic peptides, that act through two receptor subtypes, called OX1-R and OX2-R. OX1-R selectively binds orexin A, whereas OX2-R is nonselective for both orexins. High levels of OX1-R mRNA and low levels of OX2-R mRNA have been previously detected in the human adrenal cortex and medulla. Here we demonstrated by RT-PCR the expression of the OX2-R, but not the OX1-R, gene in 10 benign secreting pheochromocytomas. Both orexins A and B stimulated catecholamine secretion from pheochromocytoma slices; the maximal effective concentration was 10(-8) mol/liter. Orexins A and B (10(-8) mol/liter) increased IP3, but not cAMP production, by tumor slices, and the effect was blocked by the PLC inhibitor U-73122. The catecholamine response to 10(-8) mol/liter orexins A and B was abolished by either U-73122 or the PKC antagonist calphostin C and was unaffected by the adenylate cyclase inhibitor SQ-22536 and the PKA inhibitor H-89. Collectively, these findings suggest that orexins stimulate catecholamine secretion from human pheochromocytomas, acting through OX2-R coupled to the PLC-PKC signaling pathway.

Baseline and stimulated catecholamine secretion in normotensive patients with active acromegaly: acute effects of continuous octreotide infusion.

Alterations in catecholamine plasma levels may contribute to the cardiovascular complications of acromegaly. Since few data are available on the catecholamine secretory dynamics in active acromegaly and no evidence exists on catecholamine variations during GH decrease, we studied acromegalic patients before and during octreotide administration. We evaluated the catecholamine responses to upright posture and a cold pressure test (CPT) in 11 acromegalic (A) patients before and during continuous administration of octreotide (500 microgram/24h by s.c. pump) compared with 11 normal (N) subjects. All the acromegalic patients showed left ventricular cardiac hypertrophy. The cardiovascular responses to upright posture were similar between normal subjects and acromegalics both before and during octreotide treatment. The basal levels of norepinephrine (NE) were significantly higher in A patients compared with N subjects (423+/-45 vs 264+/-32pg/ml, P<0. 05) and decreased during therapy (291+/-32pg/ml; P<0.01). The increase in plasma NE during upright posture was significantly lower in A than in N subjects (P<0.01), but was restored to normal during octreotide treatment. CPT increased systolic and diastolic blood pressure, pulse rate and NE plasma levels in N (P<0.05) but not in A subjects both before and during octreotide treatment. Our data demonstrate the presence of increased basal NE levels in acromegalic patients with a defective sympathetic response to stimuli. Short-term octreotide infusion is able to induce a reduction in the basal levels of NE and a normalization of the catecholamine response to posture.

Leptin Directly Stimulates Catecholamine Secretion and Synthesis in Cultured Porcine Adrenal Medullary Chromaffin Cells

Leptin, a protein encoded by the ob gene, is an adipose tissue-derived signaling factor involved in body weight homeostasis. The hypothalamus is a major site of central action for leptin. However, mounting evidence indicates expression of leptin receptor mRNA in various peripheral organs including the adrenal medulla. Therefore, we investigated the effects of leptin on catecholamine secretion and synthesis in cultured porcine adrenal medullary chromaffin cells. We initially confirmed the expression of leptin receptor (Ob-Rb) mRNA in cultured porcine adrenal medullary cells. Murine recombinant leptin (≧50 nM) strongly induced the release of both epinephrine (E) and norepinephrine (NE) from chromaffin cells. Removal of external Ca2+ significantly suppressed these effects. Also, leptin (≧1 nM) enhanced nicotine-induced increases in E- and NE. Leptin (1, 10, 100 nM) significantly increased tyrosine hydroxylase (TH) (a rate-limiting enzyme in the biosynthesis of catecholamine) mRNA levels in a concentration-dependent manner. Furthermore, leptin (1, 10, 100 nM) significantly induced increases in cAMP levels, suggesting that the stimulatory effects on TH mRNA are mediated, at least in part, by the cAMP/protein kinase A pathway. These results indicate that leptin directly stimulates catecholamine release and synthesis, which in turn may potentiate the anti-obesity effects of leptin.

Dissociation of pituitary-adrenal and catecholamine activation after induced cardiac arrest and defibrillation

To avoid factors which confound attempts to characterize the neuroendocrine response to cardiac arrest, we studied the pituitary-adrenocortical and catecholamine responses to induced ventricular fibrillation (VF) and direct current cardioversion in 10 patients undergoing testing of 'implanted cardioverter defibrillator' devices under sedation. Plasma concentrations of epinephrine were increased 5 min after VF (from a mean basal of 0.39 (S.E.M. 0.09) to a peak of 0.632 (0.212) nmol litre-1; P < 0.05) but were unchanged at other times. Plasma concentrations of norepinephrine did not change at any time. Plasma concentrations of cortisol increased significantly at 10 min (from a mean of 367 (SEM 62) to 539 (64) nmol litre-1; P < 0.001) and remained increased 30 min after VF (470 (74) nmol litre-1; P < 0.05) but had returned towards baseline at 60 min, whereas plasma prolactin concentrations were increased at 5 min (from a mean of 224 (SEM 54) to 320 (63) mu. litre-1; P < 0.01) and remained increased until the end of the sampling period at 60 min (288 (65) mu. litre-1; P < 0.05). Concentrations of adrenocorticotrophic hormone (ACTH) (n = 5) tended to increase but this was not statistically significant. We conclude that a short period of cardiac arrest in lightly sedated humans activated the pituitary-adrenocortical axis but did not appear to stimulate catecholamine secretion. These findings raise questions about the nature and mechanisms of the neuroendocrine response to cardiac arrest.