Facilitation of ischaemia-induced ventricular fibrillation by catecholamines is mediated by β1 and β2 agonism in the rat heart in vitro

BACKGROUND AND PURPOSE

Antiarrhythmic β-blockers are used in patients at risk of myocardial ischaemia, but the survival benefit and mechanisms are unclear. We hypothesized that β-blockers do not prevent ventricular fibrillation (VF) but instead inhibit the ability of catecholamines to facilitate ischaemia-induced VF, limiting the scope of their usefulness.

EXPERIMENTAL APPROACH

ECGs were analysed from ischaemic Langendorff-perfused rat hearts perfused with adrenoceptor antagonists and/or exogenous catecholamines (CATs: 313 nM noradrenaline + 75 nM adrenaline) in a blinded and randomized study. Ischaemic zone (IZ) size was deliberately made small or large.

KEY RESULTS

In rat hearts with large IZs, ischaemia-induced VF incidence was high in controls. Atenolol, butoxamine and trimazosin did not affect VF at concentrations with β1 -, β2 - or α1 - adrenoceptor specificity and selectivity (confirmed in separate rat aortae myography experiments). In hearts with small IZs and low baseline incidence of ischaemia-induced VF, CATs, delivered to the uninvolved zone (UZ), increased ischaemia-induced VF incidence. This effect was not mimicked by atrial pacing, hence, not due to sinus tachycardia. However, the CATs-facilitated increase in ischaemia-induced VF was inhibited by atenolol and butoxamine (but not trimazosin), indicative of β1 - and β2 - but not α1 -adrenoceptor involvement (confirmed by immunoblot analysis of downstream phosphoproteins). CATs did not facilitate VF in low-flow globally ischaemic hearts, which have no UZ.

CONCLUSIONS AND IMPLICATIONS

Catecholamines facilitated ischaemia-induced VF when risk was low, acting via β1 - and β2 - adrenoceptors located in the UZ. There was no scope for facilitation when VF risk was high (large IZ), which may explain why β-blockers have equivocal effectiveness in humans.

Sigma-1 receptor ligands inhibit catecholamine secretion from adrenal chromaffin cells due to block of nicotinic acetylcholine receptors

Adrenal chromaffin cells (ACCs) are the neuroendocrine arm of the sympathetic nervous system and key mediators of the physiological stress response. Acetylcholine (ACh) released from preganglionic splanchnic nerves activates nicotinic acetylcholine receptors (nAChRs) on chromaffin cells causing membrane depolarization, opening voltage-gated Ca2+ channels (VGCC), and exocytosis of catecholamines and neuropeptides. The serotonin transporter is expressed in ACCs and interacts with 5-HT1A receptors to control secretion. In addition to blocking the serotonin transporter, some selective serotonin reuptake inhibitors (SSRIs) are also agonists at sigma-1 receptors which function as intracellular chaperone proteins and can translocate to the plasma membrane to modulate ion channels. Therefore, we investigated whether SSRIs and other sigma-1 receptor ligands can modulate stimulus-secretion coupling in ACCs. Escitalopram and fluvoxamine (100 nM to 1 μM) reversibly inhibited nAChR currents. The sigma-1 receptor antagonists NE-100 and BD-1047 also blocked nAChR currents (≈ 50% block at 100 nM) as did PRE-084, a sigma-1 receptor agonist. Block of nAChR currents by fluvoxamine and NE-100 was not additive suggesting a common site of action. VGCC currents were unaffected by the drugs. Neither the increase in cytosolic [Ca2+ ] nor the resulting catecholamine secretion evoked by direct membrane depolarization to bypass nAChRs was altered by fluvoxamine or NE-100. However, both Ca2+ entry and catecholamine secretion evoked by the cholinergic agonist carbachol were significantly reduced by fluvoxamine or NE-100. Together, our data suggest that sigma-1 receptors do not acutely regulate catecholamine secretion. Rather, SSRIs and other sigma-1 receptor ligands inhibit secretion evoked by cholinergic stimulation because of direct block of Ca2+ entry via nAChRs.

Antagonism of Cortex Periplocae extract-induced catecholamines secretion by Panax notoginseng saponins in cultured bovine adrenal medullary cells by drug combinations

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese Medicine (TCM) operates on the general principle that compatible components of different herbal decoction may work together to synergistically enhance therapeutic efficacy or reduce adverse effects. Cortex Periplocae is an herb that has been used in TCM clinics for a long time in the treatment of chronic heart failure. However, recently, the use of this herb has been restricted because of widespread abuse and misapplications. Radix Notoginseng is another herb that is used in TCM because of its protective role on cardiomyocytes. From our previous studies on these two herbs in a mouse model, we observed an increased LD50 after oral administration of Cortex Periplocae extract (CPE) and Panax notoginseng saponins (PNS) in a ratio of 1:1 compared with Cortex Periplocae extract used alone.

AIM OF THE STUDY

This study aimed to investigate whether there are mutual synergistic effects of the two herbal extracts, CPE and PNS, on catecholamines (CAs) secretion, and their possible underlying mechanism(s) for such effects.

MATERIALS AND METHODS

CPE and PNS were quantified by the LC-MS/MS method. HPLC-ECD was used to determine the CAs secreted into the medium by bovine adrenal medulla cells (BAMCs) and calcium influx was measured using a Calcium 4 reagent kit.

RESULTS

We found that the stimulatory effect of CPE on CAs secretion was inhibited when used together with PNS. For a better clarification of the different constituents of the extracts, a quantitative analysis was carried out. Periplocin was found to be the main active component of CPE valued as 0.99% and saponins were the principal constituents of PNS. These results also showed that CPE increased the secretion of CAs in a dose-dependent manner while the actions of PNS were seen to be inhibitory. Periplocin monomer of CPE could be implicated for the actions of CPE since it plays the role of increasing the ACh-induced CAs secretion in a calcium-dependent manner. We therefore conclude that; CPE and PNS exert antagonistic effects in regulating the concentration of intracellular calcium.

CONCLUSIONS

PNS inhibits CPE-induced CAs secretion by suppressing calcium influx in bovine adrenal medulla cells while periplocin, one of the main components of CPE has the same secretagogue effect as CPE.

A new approach to reducing postsurgical cancer recurrence: perioperative targeting of catecholamines and prostaglandins

Surgery is a crucial intervention in most cancer patients, but the perioperative period is characterized by increased risks for future outbreak of preexisting micrometastases and the initiation of new metastases-the major cause of cancer-related death. Here we argue that the short perioperative period is disproportionately critical in determining long-term recurrence rates, discuss the various underlying risk factors that act synergistically during this period, and assert that this time frame presents an unexplored opportunity to reduce long-term cancer recurrence. We then address physiologic mechanisms that underlie these risk factors, focusing on excess perioperative release of catecholamines and prostaglandins, which were recently shown to be prominent in facilitating cancer recurrence through their direct impact on the malignant tissue and its microenvironment, and through suppressing antimetastatic immunity. The involvement of the immune system is further discussed in light of accumulating evidence in cancer patients, and given the recent identification of endogenously activated unique leukocyte populations which, if not suppressed, can destroy autologous "immune-resistant" tumor cells. We then review animal studies and human correlative findings, suggesting the efficacy of blocking catecholamines and/or prostaglandins perioperatively, limiting metastasis and increasing survival rates. Finally, we propose a specific perioperative pharmacologic intervention in cancer patients, based on simultaneous β-adrenergic blockade and COX-2 inhibition, and discuss specific considerations for its application in clinical trials, including our approved protocol. In sum, we herein present the rationale for a new approach to reduce long-term cancer recurrence by using a relatively safe, brief, and inexpensive intervention during the perioperative period.

Alleviation of oxidative stress by potent and selective thioredoxin-mimetic peptides

One of the major enzymatic cell defenses providing protection from oxidative injury is the TrxR-Trx system. It consists of NADPH and thioredoxin reductase (TrxR), which maintain thioredoxin (Trx) in a reduced state. Perturbing the TrxR-Trx system with the selective TrxR inhibitor auranofin (AuF; 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato-S-(triethylphosphine) gold) induces oxidative stress by keeping Trx in its oxidized state. We have prepared a family of tri- and tetra-oligopeptides derived from the canonical CxxC motif of the Trx active site and a modified CxC motif. These Trx-mimetic compounds are N- and C-terminal-blocked peptides that consist of two cysteine residues that flank the two-amino-acid CxxC motif (CB4 and CB6) or the single-amino-acid CxC motif (CB3). Catecholamine (CA) secretion in bovine chromaffin cells, which is a highly redox sensitive process, is abolished by AuF. The Trx-mimetic peptides effectively restore CA secretion, as monitored by amperometry in single cells. They also prevent the AuF-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase. In PC12 cells, the alleviation of AuF-induced ERK1/2-MAPK phosphorylation by Trx-like peptides parallels their effect of restoring CA secretion. CB3, CB4, and CB6 act intracellularly and are significantly more potent than the traditional antioxidants NAC, GSH, DTT, AD4 (NAC-amide), and ascorbic acid. Taken together, the CxxC and CxC peptides represent a new family of potent and selective redox compounds that could serve as potential candidates for prevention and treatment of oxidative-stress-related disorders.

Involvement of brain ketone bodies and the noradrenergic pathway in diabetic hyperphagia in rats

Uncontrolled type 1 diabetes leads to hyperphagia and severe ketosis. This study was conducted to test the hypothesis that ketone bodies act on the hindbrain as a starvation signal to induce diabetic hyperphagia. Injection of an inhibitor of monocarboxylate transporter 1, a ketone body transporter, into the fourth ventricle normalized the increase in food intake in streptozotocin (STZ)-induced diabetic rats. Blockade of catecholamine synthesis in the hypothalamic paraventricular nucleus (PVN) also restored food intake to normal levels in diabetic animals. On the other hand, hindbrain injection of the ketone body induced feeding, hyperglycemia, and fatty acid mobilization via increased sympathetic activity and also norepinephrine release in the PVN. This result provides evidence that hyperphagia in STZ-induced type 1 diabetes is signaled by a ketone body sensed in the hindbrain, and mediated by noradrenergic inputs to the PVN.

Risk reduction by preventing stroke: need for blockade of angiotensin II and catecholamines?

Angiotensin (AT) II and noradrenaline play major roles in hypertension, stroke and coronary heart disease, which are themselves interlinked. Harmful effects of AT II are not blocked solely by angiotensin-converting enzyme inhibitors, as it is now evident that AT II is generated by other enzymes such as chymase. Angiotensin II also stimulates noradrenaline release modulated by presynaptic receptors on sympathetic nerves. Numerous studies have defined the action of the AT II type 1 receptor blocker (ARB) eprosartan as controlling noradrenergic and adrenergic effects, resulting from actions on the renin-angiotensin-aldosterone system and the sympathetic nervous system. Clinical studies have been carried out to assess the effects of ARBs on morbidity and mortality. The Valsartan Antihypertensive Long-term Use Evaluation (VALUE) trial compared the effects of valsartan and the calcium channel blocker (CCB) amlodipine in over 15,000 patients at high risk of a cardiac event. Results showed that blood pressure was reduced by both treatments and cardiac mortality/morbidity was similar in both groups. By contrast, the Morbidity and mortality after Stroke, Eprosartan compared with nitrendipine for Secondary prevention (MOSES) study (n = 1405) generated results which differed from the VALUE study, in that blood pressure was reduced by both eprosartan and nitrendipine, but eprosartan reduced all cardiovascular and cerebrovascular events to a greater extent than nitrendipine. It is also possible that any delayed clinical benefit of eprosartan could be due to reverse cardiac remodelling. Eprosartan, by blocking AT II receptors, reducing noradrenaline release and blocking catecholamine actions, may, therefore, provide greater protection against vascular events than CCBs or other ARBs.

Emerging drugs in neuropathic pain

Neuropathic pain is a personally devastating and costly condition affecting 3-8% of the population. Existing treatments have limited effectiveness and produce relatively frequent adverse effects. Preclinical research has identified many promising pharmacological targets; however, reliable predictors of success in humans remain elusive. At least 50 new molecular entities have reached clinical development including: glutamate antagonists, cytokine inhibitors, vanilloid-receptor agonists, catecholamine modulators, ion-channel blockers, anticonvulsants, opioids, cannabinoids, COX inhibitors, acteylcholine modulators, adenosine receptor agonists and several miscellaneous drugs. Eight drugs are in Phase III trials at present. Strategies that may show promise over existing treatments include topical therapies, analgesic combinations and, in future, gene-related therapies. Recent years have heralded an explosion of pharmaceutical development in neuropathic pain, reflecting advanced knowledge of neurobiology and a heightened perception of the commercial value of neuropathic pain therapeutics. In the interest of improving patient care, the authors recommend implementing comparative studies throughout the development process in order to demonstrate the increased value of novel agents.

Blockade of catecholamine-induced growth by adrenergic and dopaminergic receptor antagonists in Escherichia coli O157:H7, Salmonella enterica and Yersinia enterocolitica

BACKGROUND

The ability of catecholamines to stimulate bacterial growth was first demonstrated just over a decade ago. Little is still known however, concerning the nature of the putative bacterial adrenergic and/or dopaminergic receptor(s) to which catecholamines (norepinephrine, epinephrine and dopamine) may bind and exert their effects, or even whether the binding properties of such a receptor are similar between different species.

RESULTS

Use of specific catecholamine receptor antagonists revealed that only alpha, and not beta, adrenergic antagonists were capable of blocking norepinephrine and epinephrine-induced growth, while antagonism of dopamine-mediated growth was achieved with the use of a dopaminergic antagonist. Both adrenergic and dopaminergic antagonists were highly specific in their mechanism of action, which did not involve blockade of catecholamine-facilitated iron-acquisition. Use of radiolabeled norepinephrine suggested that the adrenergic antagonists could be acting by inhibiting catecholamine uptake.

CONCLUSION

The present data demonstrates that the ability of a specific pathogen to respond to a particular hormone is dependent upon the host anatomical region in which the pathogen causes disease as well as the neuroanatomical specificity to which production of the particular hormone is restricted; and that both are anatomically coincidental to each other. As such, the present report suggests that pathogens with a high degree of exclusivity to the gastrointestinal tract have evolved response systems to neuroendocrine hormones such as norepinephrine and dopamine, but not epinephrine, which are found with the enteric nervous system.

Subjective and behavioural consequences of striatal dopamine depletion in schizophrenia--findings from an in vivo SPECT study

Dysphoria is an integral part of the symptomatology of a variety of clinical states, though there is little empirical data available on the qualitative and quantitative aspects of this phenomenon. The purpose of the study was to administer alphamethyl paratyrosine (AMPT), a catecholamine depleting agent as a chemical probe to induce dysphoria, and document the ensuing changes in mental status. AMPT (4-5 g/day) was administered to a group of medication-free schizophrenic patients (n=13) over a 48 hour period, and changes in their mental status were monitored at 12 hour intervals with the Profile of Mood States (POMS), Addiction Research Center Inventory (ARCI), Drug Attitude Inventory (DAI) and other standardized rating scales. All of the subjects experienced dysphoric responses of variable severity. The profile of changes included blunted pleasure responsivity, clouded thinking, loss of motivation and lowered vigilance. Subtle subjective changes were experienced soon after the first dose of AMPT and the dysphoria steadily worsened, resulting in social withdrawal and personal distress. Subjective responses were the earliest to manifest, followed by akathisia, akinesia and rigidity. We conclude that AMPT induced dopamine depletion is a safe, rapid, reliable and reversible method of studying dysphoric states in humans. The technique is helpful in examining the phenomenology of dysphoria, the temporal relationship between subjective and behavioural consequences of dopamine depletion, and the role of dopamine in mediating subtle aspects of pleasure responsivity, which is in turn crucial to the understanding of treatment non-adherence in schizophrenia and the origins of comorbid substance abuse.

The chromogranin A fragment catestatin: specificity, potency and mechanism to inhibit exocytotic secretion of multiple catecholamine storage vesicle co-transmitters

BACKGROUND

Secretory granules of chromaffin cells and neurons co-store and release, by exocytosis, the acidic soluble protein chromogranin A (human, CHGA; rodent, Chga) along with catecholamines, neuropeptides and adenosine triphosphate (ATP). CHGA serves as a pro-protein and upon proteolytic cleavage it generates active peptides, including catestatin (human CHGA352-372), first discovered in adrenal medullary chromaffin granules. Studies in our laboratory demonstrated that catestatin acts at the nicotinic acetylcholine receptor to inhibit catecholamine secretion. However, the specificity of catestatin to exert nicotinic-cholinergic antagonism among its co-transmitters is not clearly known, nor is the potential effect of catestatin on multiple vesicle co-transmitters understood.

AIM

Here we probed the specificity of catestatin's actions among its co-transmitters: catecholamines, ATP, and neuropeptide Y (NPY).

METHODS

We studied the effects of each transmitter on exocytotic secretion of its co-transmitters from PC12 chromaffin cells, stimulating secretion by triggering physiological pathways at multiple sites.

RESULTS

We observed that, among chromaffin granule co-transmitters, only catestatin and NPY inhibited catecholamine release induced by nicotinic-cholinergic stimulation; catestatin was more than tenfold more potent than NPY in this setting. We also stimulated norepinephrine secretion by other chromaffin cell agonists: catestatin blocked norepinephrine release induced by nicotine, but not by other agents (such as membrane depolarization) acting at later stages in the secretory pathway, nor by agents acting on other receptor classes. By contrast, NPY acted less specifically, blocking norepinephrine release triggered by either nicotine or membrane depolarization. Catestatin inhibited nicotinic-cholinergic co-release of all classes of chromaffin granule co-transmitters: catecholamines, chromogranins, neuropeptides, and ATP. Naturally occurring variants of human catestatin (Gly364Ser and Pro370Leu) exhibited parallel changes in potency to inhibit secretion of catecholamines and ATP.

CONCLUSION

We conclude that, among the chromaffin granule co-transmitters, catestatin acts as the most specific and potent inhibitor of physiological pathway (nicotinic-cholinergic) stimulated secretion. Furthermore, catestatin generally inhibits nicotinically triggered exocytotic release of multiple co-transmitters from chromaffin granules. The results have physiological and pharmacological implications for co-transmission in the sympathochromaffin system.

Neuropeptide Y Induced Attenuation of Catecholamine Synthesis in the Rat Mesenteric Arterial Bed

The effect of neuropeptide Y (NPY) on the basal and nerve stimulation-induced increase in norepinephrine synthesis was studied in the isolated and perfused mesenteric arterial bed of the rat. Tyrosine hydroxylation, the rate-limiting step in catecholamine (CA) biosynthesis, was assessed by measuring the accumulation of DOPA in the perfusate/superfusate overflow after perfusion of the mesenteric arterial bed with the decarboxylase inhibitor m-hydroxybenzyl hydralazine (NSD-1015). Treatment with NDS-1015 resulted in a time-dependent increase in DOPA production and nerve stimulation (8 Hz, supramaximal voltage, 2 ms duration) increased DOPA production even further. NPY 1 to 100 nM was observed to produce a concentration-dependent attenuation in both the basal and nerve stimulation-induced increase in DOPA formation. To come to an understanding of the NPY receptor subtype mediating the inhibition of CA synthesis, the rank order of potency of a series of NPY analogs with varying selectivity for NPY receptor subtypes including intestinal polypeptide (PYY), PYY 13-36, Leu36 Pro34 NPY, human pancreatic polypeptide (h-PP), and rat pancreatic polypeptide (r-PP) were determined. In addition, the effect of various selective NPY antagonists on the inhibitory effect of NPY was also examined. These included the Y1 antagonist BIB03304, the Y2 antagonist BIIE0246, and the Y5 antagonist CGP71683. The IC50's for NPY, PYY, PYY13-36, Leu31 Pro34 NPY, and hPP in inhibiting CA synthesis were 5, 7, 15, 30, and 33 nM respectively. rPP failed to inhibit CA synthesis. All 3 of the NPY antagonists produced attenuation of the NPY-induced inhibition of CA synthesis, but it took a combination of all 3 to completely block the effect of a maximal inhibitory concentration of NPY. These results demonstrate that NPY inhibits CA synthesis in the perfused mesenteric arterial bed and can do so by activation of a variety of receptors including the Y1, Y2, and Y5.

Post burn muscle wasting and the effects of treatments

Severe burns are typically followed by a hypermetabolic response that lasts for at least 9-12 months post-injury. The endocrine status is also markedly altered with an initial and then sustained increase in proinflammatory 'stress' hormones such as cortisol and other glucocorticoids, and catecholamines including epinephrine and norepinephrine by the adrenal medulla and cortex. These hormones exert catabolic effects leading to muscle wasting, the intensity of which depends upon the percentage of total body surface area (TBSA) involved, as well as the time elapsed since initial injury. Pharmacological and non-pharmacological strategies may be used to reverse the catabolic effect of thermal injury. Non-pharmacological strategies include early excision and wound closure of burn wound, aggressive treatment of sepsis, elevation of the environmental temperature to thermal neutrality (31.5+/-0.7 degrees C), high carbohydrate, high protein continuous enteral feeding and early institution of resistive exercise programs. Pharmacological modulators of the post-burn hypermetabolic response may be achieved through the administration of recombinant human growth hormone, low dose insulin infusion, use of the synthetic testosterone analogue, oxandrolone and beta blockade with propranolol. This paper aims to review the current understanding of post-burn muscle proteolysis and the effects of clinical and pharmacological strategies currently being studied to reverse it curb these debilitating sequelae of severe burns.

The pharmacologic modulation of the hypermetabolic response to burns

Patients with burns less than 40% TBSA do not have catabolism unless sepsis develops. Those with burns more than 40% TBSA always experience catabolism, which causes metabolic derangements that persist for at least 1 year after the injury in most body tissues. The accomplishments of the past decade have placed us in the midst of an exciting paradigm shift from what used to be a primary concern (ie, mortality) to areas that are more likely to enhance the quality of life of burn survivors. Modulating postburn hypermetabolism for the burned patient is of overwhelming importance in both the immediate care stage and the rehabilitative stage. Postburn hypermetabolism cannot be completely reversed but may be manipulated by nonpharmacologic and pharmacologic means. Early burn wound excision and complete wound closure, prevention of sepsis, the maintenance of thermal neutrality for the patient by elevation of the ambient temperature, and graded resistance exercises during convalescence are simple, highly effective primary treatment goals. Although the initial burn injury and sepsis-related complications principally determine the extent of the metabolic response in burn victims, obligatory activity, background- and procedural-related pain, and anxiety also greatly increase metabolic rates. Judicious maximal narcotic support, appropriate sedation, and supportive psychotherapy are mandatory if their effects are to be minimized. Several anabolic and anticatabolic agents are available for use during immediate care and rehabilitation. Exogenous, continuous low-dose insulin infusion, beta-blockade with propranolol, and the use of the synthetic testosterone analogue oxandrolone are the most cost-effective and least toxic therapies to date. These greatly assist therapeutic minimization of the loss of lean body mass and linear growth delay and are effective in burned patients with and without sepsis. Adverse effects, cost benefits, and the ease of administration and monitoring must be examined when considering the possibility of their use.

Influence of naloxone on catecholamine release evoked by nicotinic receptor stimulation in the isolated rat adrenal gland

The present study was designed to investigate the effect of naloxone, a well known opioid antagonist, on the secretion of catecholamines (CA) evoked by cholinergic stimulation and membrane-depolarization in the isolated perfused rat adrenal glands, and to establish its mechanism of action. Naloxone (10(-6) approximately 10(-5) M), perfused into an adrenal vein for 60 min, produced dose- and time-dependent inhibition of CA secretory responses evoked by ACh (5.32 x 10(-3) M), high K+ (5.6 x 10(-2) M), DMPP (10(-4) M) and McN-A-343 (10(-4) M). Naloxone itself also failed to affect the basal CA output. In adrenal glands loaded with naloxone (3 x 10(-6) M), the CA secretory responses evoked by Bay-K-8644, an activator of L-type Ca2+ channels, and cyclopiazonic acid, an inhibitor of cytoplasmic Ca(2+)-ATPase, were also inhibited. In the presence of met-enkephalin (5 x 10(-6) M), a well known opioid agonist, the CA secretory responses evoked by ACh, high K+, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were also significantly inhibited. Taken together, these results suggest that naloxone greatly inhibits the CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors as well as that by membrane depolarization. It seems that these inhibitory effects of naloxone does not involve opioid receptors, but might be mediated by blocking both the calcium influx into the rat adrenal medullary chromaffin cells and the uptake of Ca2+ into the cytoplasmic calcium store, which are at least partly relevant to the direct interaction with the nicotinic receptor itself.

Serotonin synthesis by two distinct enzymes in Drosophila melanogaster

Annotation of the sequenced Drosophila genome suggested the presence of an additional enzyme with extensive homology to mammalian tryptophan hydroxylase, which we have termed DTRH. In this work, we show that enzymatic analyses of the putative DTRH enzyme expressed in Escherichia coli confirm that it acts as a tryptophan hydroxylase but can also hydroxylate phenylalanine, in vitro. Building upon the knowledge gained from the work in mice and zebrafish, it is possible to hypothesize that DTRH may be primarily neuronal in function and expression, and DTPH, which has been previously shown to have phenylalanine hydroxylation as its primary role, may be the peripheral tryptophan hydroxylase in Drosophila. The experiments presented in this report also show that DTRH is similar to DTPH in that it exhibits differential hydroxylase activity based on substrate. When DTRH uses tryptophan as a substrate, substrate inhibition, catecholamine inhibition, and decreased tryptophan hydroxylase activity in the presence of serotonin synthesis inhibitors are observed. When DTRH uses phenylalanine as a substrate, end product inhibition, increased phenylalanine hydroxylase activity after phosphorylation by cAMP-dependent protein kinase, and a decrease in phenylalanine hydroxylase activity in the presence of the serotonin synthesis inhibitor, alpha-methyl-(DL)-tryptophan are observed. These experiments suggest that the presence of distinct tryptophan hydroxylase enzymes may be evolutionarily conserved and serve as an ancient mechanism to appropriately regulate the production of serotonin in its target tissues.

Altering metabolism

A significant proportion of the mortality and morbidity of severe burns is attributable to the ensuing hypermetabolic response. This response can last for as long as 1 year after injury and is associated with impaired wound healing, increased infection risks, erosion of lean body mass, hampered rehabilitation, and delayed reintegration of burn survivors into society. Pharmacologic and nonpharmacologic strategies may be used to reverse the catabolic effect of thermal injury. Nonpharmacologic strategies include early excision and wound closure of burn wound, aggressive treatment of sepsis, elevation of the environmental temperature to thermal neutrality (31.5 +/- 0.7 degrees C), high carbohydrate, high protein continuous enteral feeding, and early institution of resistive exercise programs. Pharmacologic modulators of the postburn hypermetabolic response may be achieved through the administration of recombinant human growth hormone, low-dose insulin infusion, use of the synthetic testosterone analog, oxandrolone, and beta blockade with propranolol. This review article discusses these modulators of postburn metabolism.

Proof of the mysterious efficacy of ginseng: basic and clinical trials: suppression of adrenal medullary function in vitro by ginseng

The root of Panax ginseng C.A. MEYER has been reported to have an anti-stress action. Therefore, the effects of ginseng components on functions of adrenal medulla, which is one of the most important organs responsive to stress, were investigated in vitro. First, the components of ginseng were mainly divided into two fractions, that is, the saponin-rich and non-saponin fractions. The saponin-rich fraction greatly reduced the secretion of catecholamines from bovine adrenal chromaffin cells stimulated by acetylcholine (ACh), whereas the non-saponin fraction did not affect it at all. The protopanaxatriol-type saponins inhibited the ACh-evoked secretion much more strongly than the protopanaxadiol-type. On the other hand, the oleanane-type saponin, ginsenoside-Ro, had no such effect. Recent reports have demonstrated that the saponins in ginseng are metabolized and absorbed in digestive tracts following oral administration of ginseng. All of the saponin metabolites greatly reduced the ACh-evoked secretion. M4 was the most effective inhibitor among the metabolites. M4 blocked ACh-induced Na(+) influx and ion inward current into the chromaffin cells and into the Xenopus oocytes expressing human alpha3beta4 nicotinic ACh receptors, respectively, suggesting that the saponin metabolites modulate nicotinic ACh receptors followed by the reduction of catecholamine secretion. It is highly possible that these effects of ginsenosides and their metabolites are associated with the anti-stress action of ginseng.

AT-1 receptor antagonism modifies the mediation of endothelin-1, thromboxane A2, and catecholamines in the renal constrictor response to angiotensin II

OBJECTIVE

The present study investigated the consequences of partial AT(1) receptor blockade on the participation of catecholamines, thromboxane A(2) (TXA(2)), and endothelin-1 (ET-1) in the renal vasoconstriction induced by angiotensin II (Ang II).

METHODS

For this purpose, the increase in renal perfusion pressure (RPP) produced by Ang II was studied in isolated kidneys from untreated or irbesartan-treated Wistar Kyoto and spontaneously hypertensive rats (SHR), in absence or presence of the alfa-1 receptor antagonist, prazosin, the TXA(2) receptor antagonist, ifetroban, or the ET(A)/ET(B) receptor antagonist, PD145065.

RESULTS

Systolic arterial pressure (SAP) was higher (P < 0.05) in SHR than in WKY. Increases in RPP produced by Ang II were comparable in kidneys from both untreated groups. Treatment with irbesartan reduced SAP and RPP in both strains in a comparable extent. Presence of prazosin, ifetroban, or PD145065 in perfusion media reduced (P < 0.05) Ang II maximal response in all groups. Maximal inhibition of Ang II-induced vasoconstriction produced by the 3 antagonists was comparable in untreated WKY, but that of ifetroban and PD145065 was lower (P < 0.05) than that of prazosin in untreated SHR. Maximal inhibition of Ang II-induced vasoconstriction produced by the 3 antagonists was comparable in WKY treated with irbesartan, and not different to that observed in untreated WKY. Maximal inhibitory effect of the 3 antagonists was higher (P < 0.05) in treated than in untreated SHR.

CONCLUSION

The study further supports the importance of catecholamines, TXA(2), and ET-1 as mediators of the renal vasoconstriction induced by Ang II in both normotensive and hypertensive rats. Hypertensive conditions appeared to reduce the participation of TXA(2) and ET-1 in Ang II-induced vasoconstriction when compared with normotensive conditions. Chronic partial blockade of AT(1) receptors did not affect the participation of catecholamines, TXA(2), and ET-1 in normotensive rats, but increased the participation of the 3 mediators in SHR. This suggests that when AT(1) receptors are partially blocked, other vasoconstrictor factors could exert part of the renal vasoconstrictor effects of Ang II.

Conformational preferences and activities of peptides from the catecholamine release-inhibitory (catestatin) region of chromogranin A

Previous modeling (PDB 1cfk) of the catecholamine release-inhibitory "catestatin" region of chromogranin A (CgA) suggested a beta-strand/loop/beta-strand active conformation, displaying an electropositive Arg-rich loop (R(351)AR(353)GYGFR(358)). To explore this possibility, we studied NMR structures of linear and cyclic synthetic catestatin, bovine (bCgA(344-364)) or human (hCgA(352-372)). By 2-D (1)H-NMR, the structure of linear catestatin (hCgA(352-372)) exhibited the NOE pattern of a coiled loop (PDB 1lv4). We then constrained the structure, cyclizing the putative Arg-rich loop connecting the beta-strands: cyclic bCgA(350-362) ([C(0)]F(350)RARGYGFRGPGL(362)[C(+14)]). Favored conformations of cyclic bCgA(350-362) were determined by (1)H-NMR and (13)C-NMR spectroscopy. Cyclic bCgA(350-362) conformers (PDB 1n2y) adopted a "twisted-loop" conformation. Alignment between the homology model and the cyclic NMR structure showed that, while portions of the NMR structure's mid-molecule and carboxy-terminus were congruent with the homology model (RMSD, 1.61-1.91 A), the amino-terminal "twisted loop" coiled inward and away from the model (RMSD, 3.36 A). Constrained cyclic bCgA(350-362) did not exert nicotinic cholinergic antagonist activity (IC(50)>10 microM), when compared to full-length linear (IC(50) approximately 0.42-0.56 microM), or cyclic (IC(50) approximately 0.74 microM) catestatin. Thus, loss of activity in the small, constrained peptide did not result from either [Cys]-extension or cyclization, per se. While linear catestatin displays coiled character, a small cyclic derivative lost biological activity, perhaps because its amino-terminal domain deviated sharply from the predicted active conformation. These results refine the relationship between structure and function in catestatin, and suggest goals in future peptidomimetic syntheses, in particular attempts to constrain the correct amino-terminal shape for biological activity.

Prevention of catecholaminergic oxidative toxicity by 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl and its recycling complex with polynitroxylated albumin, TEMPOL/PNA

Reactive oxygen species (ROS) generated from dopamine and its oxidation products have been implicated in the pathogenesis and toxicity from treatment of Parkinson's disease-associated autonomic neuropathy, and antioxidant therapies have been proposed as treatment and prophylaxis for this disorder. However, many antioxidants are rapidly and, under physiological conditions, irreversibly oxidized, rendering them redox-inactive. We have examined the potential of 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl and polynitroxylated albumin (TEMPOL/PNA), an antioxidant complex that facilitates recycling of inactivated antioxidant to its redox-active form, as a protective agent against the toxicity of the catecholaminergic ROS generator, 6-hydroxydopamine (6-OHDA). TEMPOL/PNA is more effective against depression of activity level by 6-OHDA than the non-recycling antioxidant, TEMPOL, in a murine model of catecholaminergic oxidative damage. TEMPOL/PNA is also less toxic than TEMPOL in mice, allowing administration of higher doses of antioxidant. Both TEMPOL and TEMPOL/PNA give rise to prevention of apoptosis and to translocation of NF-kappaB from the cytoplasm to the nucleus of PC12 cells treated with 6-OHDA, but in vivo, TEMPOL/PNA maintains redox-active blood levels of TEMPOL for almost 5 h, whereas administration of TEMPOL alone results in clearance of blood redox activity within 1 h. PNA enhances the therapeutic index of TEMPOL, and the recycling antioxidant that results from their adjunctive administration may prove useful in disorders involving oxidative stress.

PTH excess may promote weight gain by impeding catecholamine-induced lipolysis-implications for the impact of calcium, vitamin D, and alcohol on body weight

Increased free intracellular calcium ([Ca(2+)](i)) in adipocytes blunts the lipolytic response to catecholamines by activating phosphodiesterase 3B - the same enzyme that mediates the antilipolytic effect of insulin - while also compromising the efficiency of insulin-stimulated glucose uptake. Physiological increases in parathyroid hormone (PTH) have been shown to increase [Ca(2+)](i) in adipocytes. These considerations may rationalize recent evidence that high dietary intakes of calcium and/or dairy products may reduce risk for obesity, diabetes, and insulin-resistance syndrome, and they predict that other dietary measures which down-regulate PTH - such as good vitamin D status, and moderation in phosphate and salt intakes - may likewise be beneficial in these respects. Consistent with this position are reports that body weight is elevated in elderly subjects with both primary and secondary hyperparathyroidism; furthermore, insulin resistance is a well-known complication of both forms of hyperparathyroidism. The fact that regular alcohol consumption is associated with decreased PTH secretion may help to explain why moderate drinkers are less prone to insulin resistance, diabetes, and - in women - obesity. Down-regulation of PTH cannot be expected to promote dramatic weight loss, but in the long-term it may lessen risk for significant weight gain and diabetes, and conceivably may potentiate the fat loss achievable with caloric restriction and/or exercise.

Cardiovascular effects of methamphetamine in Parkinson's disease patients

Cardiovascular responses after intravenous methamphetamine were assessed in 11 Parkinson's disease (PD) patients. Systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), and electrocardiogram (ECG) were monitored for 103 minutes. After methamphetamine administration, SBP and DBP increased significantly in both PD and normal controls whereas placebo had no effect. In PD patients, however, the duration of SBP and DBP responses to methamphetamine and the maximum increase from baseline was attenuated compared with the controls. A significant correlation was found between individual BP responsiveness and the Unified Parkinson's Disease Rating Scale (UPDRS) motor score. These findings suggest that in PD there is impairment of catecholamine release from peripheral sympathetic presynaptic terminals, which correlates with motor impairment.

Cotinine inhibits catecholamine release evoked by cholinergic stimulation from the rat adrenal medulla

The aim of the present study was to clarify whether cotinine affects the release of catecholamines (CA) from the isolated perfused rat adrenal gland, and to establish the mechanism of its action, in comparison with the response of nicotine. Cotinine (0.3-3 mM), when perfused into an adrenal vein for 60 min, inhibited CA secretory responses evoked by ACh (5.32 mM), DMPP (a selective neuronal nicotinic agonist, 100 microM for 2 min) and McN-A-343 (a selective muscarinic M1-agonist, 100 microM for 2 min) in dose- and time-dependent manners. However, cotinine did not affect CA secretion by high K+ (56 mM). Cotinine itself also failed to affect basal CA output. Furthermore, in the presence of cotinine (1 mM), CA secretory responses evoked by Bay-K-8644 (an activator of L-type Ca2+ channels, 10 microM) and cyclopiazonic acid (an inhibitor of cytoplasmic Ca2+-ATPase, 10 microM) were relative time-dependently attenuated. However, nicotine (30 microM), given into the adrenal gland for 60 min, initially rather enhanced CA secretory responses evoked by ACh and high K+, followed by the inhibition later, while it time-dependently depressed the CA release evoked by McN-A-343 and DMPP. Taken together, these results suggest that cotinine inhibits greatly CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, but does fail to affect that by the direct membrane-depolarization. It seems that this inhibitory effect of cotinine may be exerted by the cholinergic blockade, which is associated with blocking both the calcium influx into the rat adrenal medullary chromaffin cells and Ca2+ release from the cytoplasmic calcium store. It also seems that there is a big difference in the mode of action between cotinine and nicotine in the rat adrenomedullary CA secretion.

DHEA attenuates catecholamine secretion from bovine adrenal chromaffin cells

Dehydroepiandrosterone (DHEA) is a putative anti-stress agent and stress is associated with the secretion of catecholamine from the adrenal gland, but the effects of DHEA on catecholamine secretion are not fully understood. Using bovine chromaffin cells, we found that DHEA inhibited catecholamine secretion and cytosolic Ca(2+) ([Ca(2+)](i)) rise coupled with nicotinic acetylcholine receptor (nAChR) without exerting an effect on (3)H-nicotine binding. In the case of high K(+) stimulation, DHEA effectively suppressed secretion without affecting [Ca(2+)](i) rise. Trifluoperazine (TFP), a calmodulin inhibitor, was capable of counteracting the inhibition of DHEA on high K(+)-induced secretions. In permeabilized cells, DHEA suppressed the Ca(2+)-induced secretion. These results suggest that DHEA (a) acts as a channel blocker that suppresses Ca(2+) influx and subsequent secretions associated with nAChR, or (b) affects the intracellular secretion machinery to suppress high K(+)-induced secretions without affecting the high K(+)-induced [Ca(2+)](i) rise.

Inhibitory action of novel arginine derivative on catecholamine secretion evoked by acetylcholine from cultured bovine adrenal chromaffin cells

A novel product, 4-amino-5-guanidinopentanoic acid 15-[(4-aminobutyl)-3-aminopropylcarbamoyl] pentadecyl ester (Arg-HSA-Spm), was synthesized based on ptilomycalin A, which is one of the extracts from marine sponge. Arg-HSA-Spm contains arginine in its chemical structure. The pharmacological action of Arg-HSA-Spm on catecholamine secretion from cultured bovine adrenal chromaffin cells was examined. Arg-HSA-Spm inhibited catecholamine secretion stimulated by the physiological secretagog acetylcholine. This inhibitory action of Arg-HSA-Spm on catecholamine secretion induced by 10(-4) M acetylcholine was dose-dependent from 10(-8) M to 10(-5) M. In the presence of 3 x 10(-7) M Arg-HSA-Spm, the stimulation of catecholamine secretion observed by increasing acetylcholine up to 10(-3) M did not reach the maximal level observed without Arg-HSA-Spm. Arg-HSA-Spm at 10(-5) M suppressed both the increase in intracellular free Ca2+ level and the influx of 45Ca2+ induced by 10(-4) M acetylcholine. The Arg-HSA-Spm-induced suppression of intracellular free Ca2+ level, the influx of 45Ca2+ and catecholamine secretion were not observed in the presence of extracellular K+ at 56 mM. The results presented in this study suggested that Arg-HSA-Spm may inhibit the influx of extracellular Ca2+ into the cells, probably through its blocking action related to acetylcholine receptors, resulting in the inhibition of catecholamine secretion in adrenal chromaffin cells.

Stimulation of the α-adrenoceptor triggers the venom production cycle in the venom gland of Bothrops jararaca

The noradrenergic innervation of Bothrops jararaca venom gland is thought to be important in the production and secretion of venom. We investigated the characteristics of the α-adrenoceptor in the venom gland and its role in venom production. This receptor had relatively low sensitivity to noradrenaline (pD2=4.77±0.09, N=7)and to phenylephrine (pD2=3.77±0.06, N=11). The receptor became desensitized just after venom extraction (pD2 to phenylephrine fell to 3.27±0.02, N=6) and the sensitivity remained low for at least 15 days, returning to normal 30 days after venom extraction, by which time the snake was ready for a new cycle of venom production. Incubation of secretory cells with noradrenaline(10–4 mol l–1 for 5 min) reducedα-adrenoceptor sensitivity to the level seen after venom extraction. Blockade of catecholamine production with reserpine abolished the enlargement of the rough endoplasmic reticulum and the activation of the Golgi apparatus that are normally seen after venom extraction, and the venom production was restored by a single subcutaneous (s.c.) injection of phenylephrine (100 mg kg–1) immediately after venom extraction. Our data suggest that stimulation of the α-adrenoceptor during or shortly after biting is essential for the onset of the venom production cycle.

[Effect of catecholamines on migration and differentiation of gonadotropin releasing hormone-neurons in rats]

The GnRH producing neurons are the key link of neuroendocrine regulation of the adult reproductive system. Synthesis and secretion of GnRH are, in turn, under the afferent catecholaminergic control. Taking into account that catecholamines exert morphogenetic effects on target cells during ontogenesis, this study was aimed at investigation of the effects of catecholamines on development of GnRH neurons in rats during ontogenesis. We carried out comparative quantitative and semiquantitative analyses of differentiation and migration of GnRH neurons in fetuses of both sexes under the conditions of normal metabolism of catecholamines (administration of saline) or their pharmacologically induced deficiency (administration of alpha-methylparatyrosine). The inhibition of catecholamine synthesis from day 11 of embryogenesis led to an increasing number of GnRH neurons in rostral regions of the trajectory of their migration over the brain: in the area of olfactory tubercles on day 17 and in the area of olfactory bulb on days 18 and 21. In addition, the optical density of GnRH neurons located in the rostral regions of migration was higher in the fetuses after administration of alpha-methylparatyrosine during embryogenesis, as compared to the control. It has been concluded that catecholamines stimulate the migration of GnRH neurons and affect their differentiation.

In vitro inhibition of adrenal catecholamine secretion by steroidal metabolites of ginseng saponins

We reported previously that the protopanaxatriol saponins in Panax ginseng greatly reduce the secretion of catecholamines from bovine adrenal chromaffin cells stimulated by acetylcholine (ACh). However, protopanaxadiol saponins showed only slight inhibitory effects. Recent studies have demonstrated that oligosaccharides connected to the hydroxyl groups of the aglycone in ginseng saponins (ginsenosides) are in turn hydrolyzed in the digestive tract and absorbed into the circulation following oral administration of ginseng. Therefore, the present study was performed to investigate the effects of the major ginsenoside metabolites (M1, M2, M3, M4, M5, M11, and M12) on catecholamine secretion. All of these metabolites were shown to be potent inhibitors of ACh-evoked secretion, and M4 was the most effective. M4 blocked not only the ACh-induced Na(+) influx into the chromaffin cells but also the ACh-induced inward current into Xenopus oocytes expressing human alpha 3 beta 4 neuronal nicotinic ACh receptors. M4 reduced the secretion induced by high K(+), an activator of voltage-sensitive Ca(2+) channels, to a much lesser extent than that evoked by ACh. M1, M2, M3, M5, and M12 are protopanaxadiol saponin-derived metabolites. Therefore, these results imply that the protopanaxadiol saponins are prodrugs, and they show more potent inhibitory activity following metabolism in the digestive tract. The results further suggest that the metabolites act on nicotinic ACh receptors, blocking Na(+) influx through the receptors, and consequently reduce the catecholamine secretion from bovine adrenal chromaffin cells. The inhibitory effect of ginsenoside metabolites is probably one of the mechanisms of action responsible for the pharmacological effects of ginseng.

Parkin gene inactivation alters behaviour and dopamine neurotransmission in the mouse

Mutations of the parkin gene are the most frequent cause of early onset autosomal recessive parkinsonism (EO-AR). Here we show that inactivation of the parkin gene in mice results in motor and cognitive deficits, inhibition of amphetamine-induced dopamine release and inhibition of glutamate neurotransmission. The levels of dopamine are increased in the limbic brain areas of parkin mutant mice and there is a shift towards increased metabolism of dopamine by MAO. Although there was no evidence for a reduction of nigrostriatal dopamine neurons in the parkin mutant mice, the level of dopamine transporter protein was reduced in these animals, suggesting a decreased density of dopamine terminals, or adaptative changes in the nigrostriatal dopamine system. GSH levels were increased in the striatum and fetal mesencephalic neurons from parkin mutant mice, suggesting that a compensatory mechanism may protect dopamine neurons from neuronal death. These parkin mutant mice provide a valuable tool to better understand the preclinical deficits observed in patients with PD and to characterize the mechanisms leading to the degeneration of dopamine neurons that could provide new strategies for neuroprotection.

Regulation of nitric oxide production from macrophages by lipopolysaccharide and catecholamines

Catecholamines are elaborated in stress responses to mediate vasoconstriction, and elevate systemic vascular resistance and blood pressure. They are elaborated in disorders such as sepsis, cocaine abuse, and cardiovascular disease. The aim of the study was to determine whether catecholamines affect nitric oxide (NO) production, as NO is a vasodilator and counteracts the harmful effects of catecholamines. RAW264.7 macrophage cells were cultured with lipopolysaccharide (LPS)+/-epinephrine, norepinephrine, and dopamine at 5x10(-6)M concentrations for 24h. Supernatants were harvested for measuring NO by spectrophotometry using the Greiss reagent and cells were harvested for detecting inducible NO synthase (iNOS) by Western blot. NO production in RAW 264.7 macrophages was increased significantly by addition of LPS (0.5-10ng/ml) in a dose-dependent fashion. The NO production induced by LPS was further enhanced by epinephrine and norepinephrine, and to a lesser extent by dopamine. These increases in NO correlated with expression of iNOS protein in these cells. The enhancing effect of iNOS synthesis by epinephrine and norepinephrine on LPS-induced macrophages was down regulated by beta-adrenoceptor antagonist, propranolol, and dexamethasone. The results suggest that catecholamines have a synergic effect on LPS in induction of iNOS synthesis and NO production, and this may mediate some of the vascular effects of infection. These data support a novel role for catecholamines in disorders such as septic shock and cocaine use, and indicate that beta-adrenoceptor antagonists and glucocorticoids may be used therapeutically for modulation of the catecholamine-NO axis in disease states.

Butyl benzyl phthalate blocks Ca2+ signaling and catecholamine secretion coupled with nicotinic acetylcholine receptors in bovine adrenal chromaffin cells

Butyl benzyl phthalate (BBP), a plasticizer and an environmental pollutant, exerts genomic estrogenic-like effects via estrogen receptors. In addition to exerting genomic effects via intracellular steroid receptors, estrogen exerts non-genomic effects through interactions with membrane ion channels to lead the rapid alteration of neuronal excitability. Estradiol is known as to have modulating role on nicotinic acetylcholine receptors (nAChR). We investigated the possibility of BBP exerting non-genomic estrogenic-like effects on nAChR in bovine adrenal chromaffin cells. Our results show that BBP inhibited Ca2+ signaling induced by the nicotinic ligands carbachol, 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP) and epibatidine (IC50 levels of 4.3, 4.1, 5.4 microM, respectively) as well as high K+ solution (IC50 50.9 microM). Additionally, in the electrophysiological observations, BBP blocked the inward current coupled with nAChR under the stimulation of carbachol. We, therefore, suggest that nAChR and voltage-gated Ca2+ channels are major and minor sites, respectively, of BBP action on the plasma membrane. The inhibitory effect of BBP on nAChR was found to be both noncompetitive and reversible, remaining unchanged as nAChR ligand concentration increased and decreased after washing. BBP was 10 times more potent than estradiol in inhibiting nAChR-coupled Ca2+ signals. We conclude that BBP exerts a novel rapidly inhibitory effect on nAChR.

The group II metabotropic glutamate receptor agonist (-)-2-oxa-4-aminobicyclo[3.1.0.]hexane-4,6-dicarboxylate (LY379268) and clozapine reverse phencyclidine-induced behaviors in monoamine-depleted rats

Recent studies have indicated that the selective group II metabotropic glutamate (mGlu) receptor agonist (-)-2-oxa-4-aminobicyclo[3.1.0.]hexane-4,6-dicarboxylate (LY379268) shares common biochemical and pharmacological effects with the atypical antipsychotic clozapine. The present study aimed to further investigate these similarities (or differences) in monoamine-depleted animals by using the phencyclidine (PCP) model. Animals were pretreated 24 h before PCP administration with (i.p.) vehicle, alpha-methyl-DL-p-tyrosine methyl ester (alpha-MPT; 400 mg/kg), or DL-p-chlorophenyl-alanine methyl ester (PCPA; 300 mg/kg) injections. alpha-MPT and PCPA pretreatment significantly and selectively reduced catecholamine (dopamine and norepinepherine) or 5-hydroxytryptamine (5-HT, serotonin) and 5-hydroxyindoleacetic acid levels, respectively, in whole brain tissue. Both LY379268 and clozapine (s.c.) blocked PCP-evoked ambulatory activity and fine movements in control, alpha-MPT-, and PCPA-treated animals. In contrast, the typical antipsychotic haloperidol (s.c.) attenuated PCP behaviors in control and PCPA-pretreated animals, but was without effect in subjects pretreated with alpha-MPT. The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid/kainate-selective antagonist (3S,4aR,6R,8aR)-6-[2-(1(2)OH-tetrazole-6-yl)ethyl]decahydroisoquinoline-3-carboxylic acid (LY293558) attenuated locomotor activity in alpha-MPT-treated animals only, whereas the 5-HT(2A/2C)-selective antagonist ketanserin was effective at reducing ambulations and fine movements in control and alpha-MPT-treated animals. Taken together, these data indicate an important role for glutamatergic and serotonergic mechanisms for PCP-evoked behaviors in catecholamine-depleted animals and suggest that like clozapine, LY379268 is more effective than typical antipsychotics in these models. This study further supports the potential use of group II mGlu agonists as novel therapeutic agents in the treatment of schizophrenia.

Role of cerebral dopamine but not plasma insulin, leptin and glucocorticoid in the development of tolerance to the anorectic effect of amphetamine

Repeated treatment with amphetamine (AMPH), an anorectic agent, induced a marked anorexia on day 1 followed by a gradual reversion of this anorexia to the normal level of feeding (tolerant anorexia). The mechanism for this tolerant anorexia remained unknown because it might be related with multiple parameters, such as the change of cerebral dopamine (DA) or the plasma levels of insulin, leptin and glucocorticoid. Results revealed that plasma insulin and leptin concentrations remained unchanged during repeated AMPH administration, revealing that these two factors are not involved. Also, glucocorticoids were not required for the development of tolerant anorexia, as this effect could not be prevented by adrenalectomy. However, AMPH-induced anorexia was decreased by the pretreatment of alpha-methyl-p-tyrosine, an inhibitor of central catecholamine synthesis, and was increased by the pretreatment of nomifensine, a blocker of DA transporter that increased extracellular DA content in brain, revealing that the change of DA content could modify the action of tolerant anorexia. It is suggested that the decrease of inhibitory action of DA in brain during repeated AMPH plays a functional role in the development of tolerance to the anorectic response of AMPH.

Endocrine effects of centrally injected nociceptin in the rat

In the present study we investigated the mechanisms involved in the endocrine effect of nociceptin/orphanin FQ (OFQ) in the rat and the possible interaction between OFQ and morphine in the control of growth hormone (GH) secretion. The intracerebroventricular administration of OFQ (2.3 or 23 microg/rat, i.c.v.) in freely moving male rats caused an increase in the secretion of both GH and prolactin (PRL). The possible involvement of the catecholaminergic (CA) system was studied by administering OFQ to CA-depleted rats (rats given 200 mg/kg of alpha-methyl-p-tyrosine subcutaneously 2 h before the i.c.v. dose of OFQ). In these CA-depleted rats, administration of OFQ (23 microg/rat, i.c.v.) did not stimulate GH secretion, whereas it significantly enhanced PRL secretion. In rats anesthetized with ketamine, which induces a significant increase of GH, PRL and corticosterone secretion by activating the sympathetic tone, OFQ (23 microg/rat, i.c.v.) did not modify GH and corticosterone levels, whereas again it significantly potentiated PRL secretion. Overall these results indicate that CA system is involved in the stimulatory action of OFQ on GH but not on PRL secretion. In fact the stimulation of PRL, but not that of GH, was still evident after impairment of the CA system. Pretreatment with OFQ (23 microg/rat, i.c.v.) attenuated the GH secretion induced by morphine (1 mg/kg, given by intra-arterial injection), thus showing a negative interaction between OFQ and morphine in the control of GH secretion.

Inhibitory effects of cortical steroids and adrenocorticotropic hormone on catecholamine secretion in guinea-pig perfused adrenal glands

1 We investigated the effects of exogenously applied steroids and endogenously released cortisol on catecholamine (CA) secretion induced by cholinergic agonists in perfused guinea-pig adrenal glands. 2 Acetylcholine (ACh) and electrical stimulation induced CA secretion, which was reversibly inhibited by cortisol. Adrenocorticotropic hormone (ACTH) increased the concentration of cortisol in the perfusion effluent and partly inhibited the secretory response to ACh. 3 Cortisol or aldosterone dose-dependently inhibited secretory responses to nicotine and muscarine. These inhibitory effects were not antagonized by mifepristone and spironolactone, respective cortisol and aldosterone receptor blockers. 4 Dexamethasone, cortisone, corticosterone, 11-deoxycortisol, 11-deoxycorticosterone, prednisolone and cholesterol inhibited nicotine-evoked CA secretion. The secretory response to muscarine was inhibited by these compounds except for dexamethasone and prednisolone. 5 Dexamethasone, cortisol and aldosterone had no effect on CA secretion induced by high KCl. 6 These results suggest that steroids affect nicotinic and muscarinic ACh receptor-mediated responses through distinct mechanisms, and that cortisol released from the adrenal cortex inhibits CA secretion from the adrenal medulla.

General pharmacological profile of the novel muscarinic receptor agonist SNI-2011, a drug for xerostomia in Sjögren's syndrome. 2nd communication: effects on somatic nervous system and on autonomic nervous system and smooth muscle

A novel muscarinic receptor agonist SNI-2011 ((+/-)-cis-2-methylspirol[1,3-oxathiolane-5,3'-quinuclidine] monohydrochloride hemihydrate, cevimeline, CAS 153504-70-2), is a candidate therapeutic drug for xerostomia in Sjögren's syndrome. The general pharmacological properties of this drug on the somatic nervous system and on the autonomic nervous system and smooth muscle were investigated in mice, rats, guinea pigs, rabbits and cats. 1. Somatic nervous system: SNI-2011 had no effect on the neuromuscular junction in rats and no muscle relaxant effect in mice. No surface anesthetic effect was observed in guinea pigs, but infiltration anesthetic effect was found after intracutaneous injection of solution (1% or higher). 2. Autonomic nervous system and smooth muscle: SNI-2011 tended to cause mydriasis at 3 mg/kg i.v. or higher in rabbits and dose-dependently caused mydriasis at 10 mg/kg p.o. or higher in rats. Mydriasis in rats was also observed by ophthalmic instillation, caused via the peripheral muscarinic acetylcholine receptors. SNI-2011 elevated the base line tension of nictitating membrane in cats when it was injected intravenously at 3 mg/kg or higher. In the smooth muscle, SNI-2011 increased the spontaneous movement of isolated rabbit ileum (1 x 10(-6) mol/l or higher), contractions of isolated guinea pig ileum (1 x 10(-6) mol/l or higher) and isolated guinea pig trachea (3 x 10(-6) mol/l or higher). SNI-2011 relaxed the histamine- and noradrenaline-induced contractions of isolated guinea pig aorta and augmented noradrenaline- and phenylephrine-induced contractions of isolated rat vas deferens. These effects were induced by relatively higher concentrations only i.e. 1 x 10(-5) mol/l or higher. From these results, SNI-2011 has muscarinic side effects on the somatic nervous system and on the autonomic nervous system and smooth muscle, however, in the case of oral administration, that is clinical administration route, SNI-2011 caused no muscarinic side effect at the effective doses needed for saliva secretion.

Prolonged inhibition of presynaptic catecholamine synthesis with alpha-methyl-para-tyrosine attenuates the circadian rhythm of human TSH secretion

OBJECTIVE

Originating from the pituitary gland, TSH secretion is regulated predominantly by thyroid-releasing hormone (TRH) neurons located in the hypothalamus. Norepinephrine and dopamine have important effects in modulation of TSH secretion. An inhibitor of catecholamine synthesis, alpha-methyl-para-tyrosine (AMPT) has been used in several studies of the regulation of human TSH secretion. The short-term effects (<8 hours) of low doses of AMPT include stimulation of pituitary TSH secretion by selective lowering of brain dopamine levels. After prolonged administration of AMPT (>24 hours), theoretically both dopamine and norepinephrine levels are lowered significantly in the brain, although this has not been reported previously.

METHODS

Nine subjects (five women and four men) received a total of five 1-g doses of AMPT or five 50-mg doses of promethazine (active placebo) over 28 hours in a randomized, double-blind, placebo-controlled crossover design in which the active and control tests were separated by 4-6 weeks. Blood samples were obtained over 24 hours (18 time points) on day 2 of each condition.

RESULTS

Changes in prolactin secretion and 6-hydroxymelatonin sulfate excretion indirectly showed the effects of AMPT on dopamine and norepinephrine. The typical circadian rhythm of TSH secretion was blunted by AMPT throughout the night; at ten time points, the difference between the two groups was statistically significant (P <.01). The long-term effects of repeated doses of AMPT were inhibition of TSH secretion and significant attenuation of the circadian rhythm of TSH. Additionally, AMPT induced low norepinephrine levels, which counteracted the stimulatory effect of low dopamine levels on TSH.

CONCLUSION

Through its inhibitory effect on TRH, norepinephrine appeared to be involved in the regulation of TSH.

Mechanism by which wortmannin and LY294002 inhibit catecholamine secretion in the rat adrenal medullary cells

The effects of wortmannin and LY294002, inhibitors of PI(3)-kinase, in secretagogue-stimulated rat adrenal chromaffin cells loaded with Calcium Green-1 were studied by simultaneously measuring changes in the fluorescence intensity of the indicator (Ca-response) and in the release of catecholamine (secretory response). Before application of these agents, the profile of the secretory response evoked by a 10-min stimulation with 30 mM K(+)] was approximated by the k th (2.6 on average) power of that of the Ca-response. Both agents dose-dependently inhibited the high-K(+)-elicited Ca-response and secretory response in a similar mode to which the k th power relation was preserved despite the occurrence of profound changes in the shapes and sizes of these two responses. The L-type Ca(2+)-channel blocker PN200-110 inhibited the high-K(+)-evoked responses in a similar fashion. Thus, it is likely that wortmannin and LY294002 inhibit high-K(+)-evoked CA secretion by inhibiting a Ca(2+)-influx through voltage-dependent Ca(2+)channels. Although regulation of L-type Ca(2+)channel activity via PI(3)-kinase has been reported in vascular myocytes, this possibility may be limited in the present case since the doses of LY294002 and wortmannin used to inhibit the secretory response are much higher than IC(50)'s for inhibition of PI(3)-kinase with these agents. Compared with the high-K(+)-elicited responses, muscarine-evoked Ca-responses and secretory responses were more strongly inhibited by wortmannin, but less affected by LY294002. The differential effects suggest that the inhibition of the muscarine-evoked secretion by these agents i s not associated with the inhibition of PI(3)-kinase.

Monoamine pharmacology of the lobster cardiac ganglion

Monoamine agonists and antagonists were applied to the lobster cardiac ganglion in an attempt to clarify the different actions of 5-hydroxytryptamine (5HT) and dopamine (DA) on this rhythmic pattern generator. Experiments were designed to determine whether the similar responses to 5HT and DA applied to the anterior region of the ganglion could be separated by pharmacological approaches, and whether the different responses to 5HT applied to the anterior and posterior regions of the ganglion could be attributed to mediation by different receptors. A small number of the 5HT agonists which were tested mimic the effects of 5HT, in that they increase the frequency of bursting and decrease burst duration when applied to the whole ganglion, but decrease burst frequency and increase burst duration when applied only to the posterior half. Other 5HT agonists decrease frequency and prolong bursts when applied to the whole ganglion. Of the DA agonists tested, none acts as DA itself does. Rather, they mimic the effects of 5HT applied to the posterior ganglion, by slowing bursting and prolonging bursts. The actions of agonists do not correspond in any clear way to the receptor specificities as defined in vertebrates. Most antagonists tested do not show similar specificities to their effects in vertebrates. In particular, most of the DA antagonists tested are more effective in blocking exogenous 5HT than DA. One monoamine agonist directly alters the properties of endogenous burst-organizing potentials (driver potentials) in the motorneurons of the ganglion.

Lipopolysaccharide-induced tumor necrosis factor-alpha release is controlled by the central nervous system

OBJECTIVE

Lipopolysaccharide (LPS) injection in mammals orchestrates the release of many proinflammatory and anti-inflammatory cytokines. Intravenous administration of 0.2 mg/kg of LPS into unanesthetized rats with indwelling jugular catheters provoked a rapid, 50-fold increase in plasma tumor necrosis factor (TNF)-alpha within 30 min, which declined by 60% by 120 min. To test our hypothesis that such a rapid increase of TNF-alpha would be either neurally or hormonally controlled, the effect on TNF-alpha release of anesthesia (ketamine/acepromazine/xylazine) and catecholaminergic agonists and antagonists, either alone or in the presence of LPS, was determined.

METHODS

Rats bearing indwelling external jugular catheters were injected with the test drug or saline after removal of 0.6 ml of blood (-10 min). At time zero, LPS or saline was administered. Thereafter, blood samples were drawn at 15, 30, 120, 240 and 360 min. TNF-alpha was measured by immunoassay.

RESULTS

Among all the drugs tested, only propranolol increased plasma TNF-alpha. Anesthesia significantly blunted the LPS-induced TNF-alpha peak by 50%. Isoproterenol, a beta-adrenergic agonist, also blocked LPS-induced TNF-alpha release by 70% at 30 min and 90% at 120 min. On the contrary, propranolol, a beta-receptor blocker, induced a highly significant 3-fold increase in plasma TNF-alpha concentrations at 30 min and augmented the response to LPS 2-fold after endotoxin injection. Phentolamine, an alpha-receptor blocker, decreased the LPS-induced TNF-alpha release by 57% at 30 min. Similarly, alpha-bromoergocryptine, a dopamine D2 receptor agonist, decreased the LPS-induced TNF-alpha peak by 70% at 30 min and 50% at 120 min.

CONCLUSIONS

We conclude that TNF-alpha is at least in part neurally controlled since the anesthetic blocked its response to LPS. The fact that isoproterenol decreased the LPS-induced TNF-alpha release, whereas propranolol augmented basal and LPS-induced release suggests that the sympathetic nervous system inhibits basal and LPS-stimulated TNF-alpha release via beta-adrenergic receptors. Since phentolamine blocked LPS-induced release, this release may be induced, in part at least, by LPS-stimulated adrenergic drive acting on alpha-adrenergic receptors. The suppressive action of bromoergocryptine, a dopamine D2 receptor agonist, on LPS-induced TNF-alpha release may be mediated in part by suppression of prolactin release, which triggers TNF-alpha release.

Inactivation of catecholamines by superoxide gives new insights on the pathogenesis of septic shock

A major feature of septic shock is the development of a vascular crisis characterized by nonresponsiveness to sympathetic vasoconstrictor agents and the subsequent irreversible fall in blood pressure. In addition, sepsis, like other inflammatory conditions, results in a large increase in the production of free radicals, including superoxide anions (O(2)) within the body. Here we show that O(2) reacts with catecholamines deactivating them in vitro. Moreover, this deactivation would appear to account for the hyporeactivity to exogenous catecholamines observed in sepsis, because administration of a superoxide dismutase (SOD) mimetic to a rat model of septic shock to remove excess O(2) restored the vasopressor responses to norepinephrine. This treatment with the SOD mimetic also reversed the hypotension in these animals; suggesting that deactivation of endogenous norepinephrine by O(2) contributes significantly to this aspect of the vascular crisis. Indeed, the plasma concentrations of both norepinephrine and epinephrine in septic rats treated with the SOD mimetic were significantly higher than in untreated rats. Interestingly, the plasma concentrations for norepinephrine and epinephrine were inversely related to the plasma concentrations of adrenochromes, the product of the autoxidation of catecholamines initiated by O(2). We propose, therefore, that the use of a SOD mimetic represents a new paradigm for the treatment of septic shock. By removing O(2), exogenous and endogenous catecholamines are protected from autoxidation. As a result, both hyporeactivity and hypotension are reversed, generation of potentially toxic adrenochromes is reduced, and survival rate is improved.

Inhibition by neuroprotective drug NS-7 of nicotine-induced 22Na(+) influx, 45Ca(2+) influx and catecholamine secretion in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells, NS-7 [4-(4-fluorophenyl)-2-methyl-6-(5-piperidinopentyloxy) pyrimidine hydrochloride], a newly-synthesized neuroprotective drug, inhibited nicotine-induced 22Na(+) influx via nicotinic receptors (IC(50)=15.5 microM); the suppression by NS-7 was observed in the presence of ouabain, an inhibitor of Na(+),K(+)-ATPase, and was not attenuated upon the washout of NS-7. NS-7 decreased nicotine-induced maximum influx of 22Na(+) without altering the EC(50) value of nicotine. Also, NS-7 diminished nicotine-induced 45Ca(2+) influx via nicotinic receptors and voltage-dependent Ca(2+) channels (IC(50)=14.1 microM) and catecholamine secretion (IC(50)=19.5 microM). These results suggest that NS-7 produces noncompetitive and long-lasting inhibitory effects on neuronal nicotinic receptors in adrenal chromaffin cells, and interferes with the stimulus-secretion coupling.