Novel autocrine feedback control of catecholamine release. A discrete chromogranin a fragment is a noncompetitive nicotinic cholinergic antagonist

Catecholamine secretory vesicle core proteins (chromogranins) contain an activity that inhibits catecholamine release, but the identity of the responsible peptide has been elusive. Size-fractionated chromogranins antagonized nicotinic cholinergic-stimulated catecholamine secretion; the inhibitor was enriched in processed chromogranin fragments, and was liberated from purified chromogranin A. Of 15 synthetic peptides spanning approximately 80% of chromogranin A, one (bovine chromogranin A344-364 [RSMRLSFRARGYGFRGPGLQL], or catestatin) was a potent, dose-dependent (IC50 approximately 200 nM), reversible secretory inhibitor on pheochromocytoma and adrenal chromaffin cells, as well as noradrenergic neurites. An antibody directed against this peptide blocked the inhibitory effect of chromogranin A proteolytic fragments on nicotinic-stimulated catecholamine secretion. This region of chromogranin A is extensively processed within chromaffin vesicles in vivo. The inhibitory effect was specific for nicotinic cholinergic stimulation of catecholamine release, and was shared by this chromogranin A region from several species. Nicotinic cationic (Na+, Ca2+) signal transduction was specifically disrupted by catestatin. Even high-dose nicotine failed to overcome the inhibition, suggesting noncompetitive nicotinic antagonism. This small domain within chromogranin A may contribute to a novel, autocrine, homeostatic (negative-feedback) mechanism controlling catecholamine release from chromaffin cells and neurons.     

Desensitization of catecholamine release. The novel catecholamine release-inhibitory peptide catestatin (chromogranin a344-364) acts at the receptor to prevent nicotinic cholinergic tolerance

Nicotinic cholinergic receptors undergo desensitization upon repeated or prolonged exposure to agonist. We investigated the effects of a novel chromogranin A catecholamine release-inhibitory fragment, catestatin (chromogranin A344-364), on agonist-induced desensitization of catecholamine release from pheochromocytoma cells. In a dose-dependent fashion, the nicotinic antagonist catestatin blocked agonist desensitization of both catecholamine release (IC50 approximately 0.24 microM) and 22Na+ uptake (IC50 approximately 0.31 microM), the initial step in nicotinic cationic signal transduction; both secretion inhibition and blockade of desensitization were noncompetitive with agonist. Desensitizing effects of the nicotinic agonists nicotine and epibatidine were blocked. This antagonist action was specific to desensitization by nicotinic agonists, since catestatin did not block desensitization of catecholamine release induced by agents which bypass the nicotinic receptor. Hill plots with slopes near unity suggested noncooperativity for catestatin effects on both nicotinic responses (secretory antagonism and blockade of desensitization). Human, bovine, and rat catestatins (as well as substance P) had similar potencies. IC50 values for secretion inhibition and blockade of desensitization paralleled each other (r = 0.76, n = 10 antagonists, p = 0.01) for several noncompetitive nicotinic antagonists. Peptide nicotinic antagonists (catestatins, substance P) were far more potent inhibitors of both secretion (p = 0.019) and desensitization (p = 0.005) than nonpeptide antagonists (trimethaphan, hexamethonium, procaine, phencyclidine, cocaine, or clonidine), and the peptides displayed enhanced selectivity to block desensitization versus secretion (p = 0.003). We conclude that catestatin is a highly potent, dose-dependent, noncompetitive, noncooperative, specific inhibitor of nicotinic desensitization, an effect which may have implications for control of catecholamine release.     

The microbicidal effect of aldehydes and aldehyde combinations

The effects of enflurane anesthesia on adrenal medullary catecholamine secretion and on the pressor effect of splanchnic-nerve stimulation were studied in cats given pentobarbital for basal anesthesia. Inhalation of enflurane, 1.2 and 2.2 per cent, caused dose-related inhibition of both spontaneous catecholamine release and secretion evoked by splanchnic-nerve stimulation. During inhalation of 2.2 per cent enflurane spontaneous release of epinephrine was decreased to 19 and 25 per cent, respectively, of the initial values, and the stimulated release was decreased to 30 and 15 per cent, respectively. Enflurane also inhibited the pressor effect of splanchnic-nerve stimulation, whereas that of norepinephrine was not changed significantly. These results are similar to those previously obtained with halothane and methoxyflurane. It is concluded that the decrease in catecholamine secretion caused by enflurane is in part due to a direct effect on the chromaffin cell, namely to an inhibition of the secretion-stimulating effect of acetylcholine released from splanchnic nerves.     

Pressor effects elicited from the periaqueductal grey, and dorsal and ventrolateral medulla in cats are independent from cerebellar mechanisms

Cats were anesthetized with chloralose (35 mg/kg, i.p.) and urethane (350 mg/kg, i.p.). In 5 cats, the pressor regions of periaqueductal grey (PAG) of the midbrain were stimulated electrically (rectangular pluses, 80 Hz, 0.5 ms, 100-150 microA). In another 6 cats, the pressor regions of both dorsal medulla (DM) and ventrolateral medulla (VLM) previously located by electrical stimulation in the same cat were stimulated by sodium glutamate (Glu, 0.25 M, 100 nl). After control stimulation, the superior, middle and inferior cerebellar peduncles on both sides were transected while the stimulating electrodes were maintained in the same position. Changes of systemic arterial pressure (SAP) and plasma norepinephrine (NE) and epinephrine (EP) following stimulations of the PAG, DM or VLM were compared before and after transections. It was found that the transection did not cause significant changes in the resting SAP and plasma NE and EP and also the induced pressor responses, namely the increases of above parameters. Findings suggest that the sympathetic vasomotor effect and adrenomedullary secretion resulted from stimulations of both DM and VLM and possibly PAG are independent from the cerebellar mechanism.     

Effect of unilateral vestibular stimulation on histamine release from the hypothalamus of rats in vivo

1. We investigated the effect of unilateral vestibular stimulation on histamine release from the anterior hypothalamic area of urethan-anesthetized rats in vivo, using a brain microdialysis method coupled with high-performance liquid chromatography fluorometry. 2. The histamine release was increased to approximately 180% of the basal release by the electrical stimulation of the inner ear with 1 Hz, 500 microA, and 200 ms for 20 min. This effect was dependent on the current intensity. 3. Activation of the unilateral horizontal semicircular canal by middle ear irrigation for 15 min with 45 degrees C water increased the histamine release to approximately 200% of the basal release. 4. Irrigation of the middle ear with ice water for 15 min increased the histamine release to approximately 190% of the basal release. 5. The histamine release was not changed by the irrigation of the middle ear with 37 degrees C water and the irrigation of the auricle with ice water, which suggests that neither somatosensory stimulation to the middle ear nor nonspecific cold stress affects the histamine release. 6. All these findings suggest that the sensory mismatch signals induced by caloric stimulation and unilateral electrical vestibular stimulation activate the histaminergic neuron system in the brain.     

Studies on the extra-hepatic effects of glucagon in the eviscerated rat

The in vivo effects of glucagon on the metabolism of extra-hepatic tissues have been investigated in eviscerated, functionally hepatectomized rats with intact kidneys. In these animals, even pharmacological amounts of exogenous glucagon did not significantly alter plasma glucose, FFA, or amino acids, compared with saline treatment. The possible secondary release of adrenal catecholamines following such doses of glucagon appeared to be similarly ineffective in increasing the peripheral tissue mobilization of substrates. It was only when the eviscerated animals were pretreated with insulin that the subsequent administration of glucagon or epinephrine elicited significant elevations in plasma FFA. The concomitant evisceration and adrenalectomy did not produce results which were significantly different from evisceration alone. Both kinds of animals required insulin pretreatment before a lipolytic response to glucagon or epinephrine could be demonstrated. This suggests that severe insulin insufficiency itself elicits almost maximum catabolism in these animals and that the further addition of other catabolic hormones such as glucagon or epinephrine cannot increase these catabolic effects, as manifest in plasma concentrations of FFA. These data show an extra-hepatic lipolytic effect of glucagon in vivo, but do not illuminate the significance of this effect in the intact animal.     

Epinephrine proactive retardation of amygdala-kindled epileptogenesis.

Examined, in 3 experiments with 208 male Sprague-Dawley rats, the dose and temporal characteristics of epinephrine's retardant effects on the rate of kindling. In Exp I, the effects of lower doses of epinephrine (0.01, 0.1, or 1.0 mg/kg) on the development of kindled seizures was evaluated when the drug was administered 30 min or 24, 48, or 72 hrs before the 1st kindling trial. In Exp II, the effects of epinephrine (0.1 or 1.0 mg/kg) seizures were explored when the drug was administered to partially or fully kindled Ss. In Exp III, plasma catecholamine levels and cardiovascular responses were examined at 15 min and 1, 3, 5, and 24 hrs after epinephrine injection (0.1 or 1.0 mg/kg). Results indicate that epinephrine had dose- and time-dependent influences on amygdala kindling and acted primarily on the processes that established kindling and not on the kindled seizures per se. It is suggested that changes in plasma catecholamine levels, elevation in arterial blood pressure, and increase in heart rate do not appear to be sufficient explanations for epinephrine's long-term proactive attenuation of kindling. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Catecholamine secretory vesicles. Augmented chromogranins and amines in secondary hypertension

Chromogranins A and B are major soluble proteins in chromaffin granules. Their adrenomedullary content is increased in the spontaneously (genetic) hypertensive rat. Is augmented catecholamine vesicular storage of the chromogranins a specific feature of genetic hypertension? To explore this question, we measured chromogranin A immunoreactivity, using a novel, synthetic peptide radioimmunoassay, in rat adrenal medullas 4-6 weeks after induction of the two-kidney, one clip Goldblatt model of renovascular hypertension and in unmanipulated control animals. We also measured messenger RNAs of chromogranins A and B and dopamine beta-hydroxylase by Northern blot. Immunoreactive adrenal chromogranin A was 3.3-fold higher (p < 0.01) in clipped rat adrenals. Adrenal catecholamine concentrations and phenylethanolamine-N-methyltransferase activity were also higher in clipped rats. Adrenal dopamine beta-hydroxylase activity (both membrane-bound and soluble forms) and corticosterone (glucocorticoid) concentration did not significantly differ between the groups. Adrenal medullary chromogranin A messenger RNA levels in clipped rats were 3.2-fold higher (p = 0.029) than those in the control group, and chromogranin B messenger RNA levels were 4.6-fold higher (p = 0.05). Dopamine beta-hydroxylase messenger RNA levels were 2.9-fold higher (p = 0.038). Thus, augmented synthesis and storage of adrenomedullary chromogranins A and B, catecholamines, and their biosynthetic enzymes appear to be characteristic of both acquired and genetic hypertension.     

Catecholamine response during 12 days of high-altitude exposure (4, 300 m) in women

Atrial natriuretic peptide (ANP) has been considered a potential candidate participating in the inhibitory control of pituitary-adrenal secretory activity. Here, we investigated the influence of ANP, infused at two different doses and over infusion intervals of two different durations, on the release of ACTH and cortisol after stimulation with CRH and with combined administration of CRH and vasopressin (VP). In young healthy men, three experiments were conducted. In Exp I, ACTH/cortisol secretory responses to CRH (50 microg) were examined during and after a 45-min period of ANP infusion at a rate of 4.4 microg/min (starting 15 min before CRH injection). In Exp II, ACTH/cortisol secretory responses to CRH (50 microg) were examined during and after a 90-min infusion period of ANP administered at rates of 4.4 and 8.8 microg/min. In Exp III, ANP was infused at a rate of 4.4 microg/min over 90 min, but instead of CRH, a combined administration of CRH (50 microg) and VP (0.5 IU infused within 5 min) was employed to stimulate ACTH/cortisol release. ANP diminished pituitary-adrenal secretory responses within the first hour after stimulation with exogenous secretagogues. Thereafter, the effect of ANP turned in the opposite direction, with distinctly enhanced concentrations of ACTH and cortisol during the third hour after stimulation. The inhibitory effect of ANP during the first hour of the pituitary-adrenal response was more pronounced on concentrations of cortisol than ACTH and was also more pronounced after combined administration of CRH/VP than after stimulation with CRH alone. Increasing the dose of ANP enhanced the late stimulatory effect on ACTH/cortisol release, thereby terminating the early period of inhibited ACTH/cortisol release more abruptly. The late stimulatory effect was enhanced with prolonged infusion of ANP. In addition, it was associated with reduced hematocrit, increased urine volumes collected, increased heart rate, and enhanced plasma VP concentrations. Together, these changes suggest that the late stimulatory effect of ANP on ACTH/cortisol release reflects an effect secondary to its hypovolemic actions. This stimulatory effect originating from peripheral systemic actions of ANP after exogenous administration appears to override a more direct inhibitory action of the peptide on pituitary-adrenal secretory activity. Therefore, we would expect that with localized release into portal hypophyseal blood the inhibitory component of the action of ANP on pituitary-adrenal secretory activity prevails.     

5-hydroxytryptamine inhibits pressor responses to preganglionic sympathetic nerve stimulation in pithed rats

5-Hydroxytryptamine (5-HT) inhibits contractile responses to adrenergic nerve stimulation in several blood vessels and organs. We have now investigated the potential ability of 5-HT to inhibit the pressor responses caused by preganglionic sympathetic stimulation (T7-T9) in pithed rats. Sympathetic stimulation (0.03, 0.1, 0.3, 1 and 3 Hz) resulted in frequency-dependent increases in diastolic blood pressure; these effects were augmented after i.v. treatment with desipramine (50 micrograms/kg). During continuous infusions of 5-HT (1.8, 3.1, 5.6 and 10 micrograms/kg.min, i.v.), but not of saline, the pressor responses were dose-dependently inhibited in both control and desipramine-pretreated rats; this inhibitory effect of 5-HT was significantly more pronounced at lower frequencies of stimulation. In contrast, the above infusions of 5-HT did not inhibit the pressor responses induced by i.v. bolus injections of exogenous norepinephrine (up to 3 micrograms/kg). Taken together, the above findings suggest an operative 5-HT-induced prejunctional inhibition of sympathetic nerve activity on the systemic vasculature in vivo.     

Adrenomedullary secretion of epinephrine is increased in mild essential hypertension

To assess whether patients with mild essential hypertension have excessive activities of the sympathoneuronal and adrenomedullary systems, we examined total body and forearm spillovers and norepinephrine and epinephrine clearances in 47 subjects with mild essential hypertension (25 men, 22 women, aged 38.1 +/- 6.7 years) and 43 normotensive subjects (19 men, 24 women, aged 36.5 +/- 5.9 years). The isotope dilution method with infusions of tritiated norepinephrine and epinephrine was used at rest and during sympathetic stimulation by lower body negative pressure at -15 and -40 mm Hg. Hypertensive subjects had a higher arterial plasma epinephrine concentration (0.20 +/- 0.01 nmol.L-1: mean +/- SE) than normotensive subjects (0.15 +/- 0.01) (P < .01). The increased arterial plasma epinephrine levels appeared to be due to a higher total body epinephrine spillover rate in the hypertensive subjects (0.23 +/- 0.02 nmol.min-1.m-2) than the normotensive subjects (0.18 +/- 0.01) (P < .05) and not to a decreased plasma clearance of epinephrine. The arterial plasma norepinephrine level, total body and forearm norepinephrine spillover rates, and plasma norepinephrine clearance were not altered in the hypertensive subjects. The responses of the catecholamine kinetic variables to lower body negative pressure were not consistently different between normotensive and hypertensive individuals. These data indicate that individuals with mild essential hypertension (1) have elevated arterial plasma epinephrine concentrations that are due to an increased total body epinephrine spillover rate, indicating an increased adrenomedullary secretion of epinephrine; (2) have no increased generalized sympathoneuronal activity and no increased forearm norepinephrine spillover; and (3) have similar responses of both the sympathoneuronal and adrenomedullary systems to sympathetic stimulation by lower body negative pressure.     

Histamine-evoked chromaffin cell scinderin redistribution, F-actin disassembly, and secretion: in the absence of cortical F-actin disassembly, an increase in intracellular Ca2+ fails to trigger exocytosis

Histamine is a known chromaffin cell secretagogue that induces Ca(2+) -dependent release of catecholamines. However, conflicting evidence exists as to the source of Ca2+ utilized in histamine-evoked secretion. Here we report that histamine-H1 receptor activation induces redistribution of scinderin, a Ca(2+)-dependent F-actin severing protein, cortical F-actin disassembly, and catecholamine release. Histamine evoked similar patterns of distribution of scinderin and filamentous actin. The rapid responses to histamine occurred in the absence of extracellular Ca2+ and were triggered by release of Ca2+ from intracellular stores. The trigger for the release of Ca2+ was inositol 1,4,5-trisphosphate because U-73122, a phospholipase C inhibitor, but not its inactive isomer (U-73343), inhibited the increases in IP3 and intracellular Ca2+ levels, scinderin redistribution, cortical F-actin disassembly, and catecholamine release in response to histamine. Thapsigargin, an agent known to mobilize intracellular Ca2+, blocked the rise in intracellular Ca2+ concentration, scinderin redistribution, F-actin disassembly, and catecholamine secretion in response to histamine. Calphostin C and chelerythrine, two inhibitors of protein kinase C, blocked all responses to histamine with the exception of the release of Ca2+ from intracellular stores. This suggests that protein kinase C is involved in histamine-induced responses. The results also show that in the absence of F-actin disassembly, rises in intracellular Ca2+ concentration are not by themselves capable of triggering catecholamine release.     

Stimulation of the sympathetic perimesenteric arterial nerves releases neuropeptide Y potentiating the vasomotor activity of noradrenaline: involvement of neuropeptide Y-Y1 receptors

Neuropeptide Y (NPY) appears to be involved in the sympathetic regulation of vascular tone. To assess the putative role of NPY in mesenteric circulation, the release and biological effect of NPY were examined after electrical stimulation of perimesenteric arterial nerves. Nerve stimulation with trains of 2-30 Hz increased the perfusion pressure of the arterially perfused rat mesenteric bed in a frequency- and time-dependent fashion. Trains of 15-30 Hz significantly displaced to the left, approximately threefold, the noradrenaline (NA)-induced pressor concentration-response curve, in addition to increasing significantly its efficacy. Perfusion with 10 nM exogenous NPY mimicked the electrical stimulation effect, causing a threefold leftward shift of the NA concentration-response curve and increasing the maximal NA response. These effects were antagonized by 100 nM BIBP 3226, indicating the activity of NPY-Y1 receptors. Electrical stimulation of the perimesenteric nerves released immunoreactive NPY (ir-NPY) in a frequency-dependent fashion; the ir-NPY coelutes with synthetic NPY as confirmed by HPLC. Both the electrically induced pressor response and the calcium-dependent release of NPY were obliterated in preparations perfused with 1 microM guanethidine or in rats pretreated intravenously for 48 h with 6-hydroxydopamine, thus revealing the sympathetic origin of these phenomena. Only a small proportion of the total NPY content in the perimesenteric arterial nerves is released after electrical stimulation. Chromatographic studies of the physiological sources of the ir-NPY support that NPY fragments are generated via peptidase degradation. The present findings demonstrate that NPY is released from the perimesenteric arterial sympathetic nerves and acts, via the activation of NPY-Y1 receptors, as the mediator responsible for the potentiation of NA's effect on perfusion pressure in the isolated rat mesenteric bed.     

Histamine H3-receptor-mediated inhibition of calcitonin gene-related peptide release from cardiac C fibers. A regulatory negative-feedback loop

Antidromic stimulation of cardiac sensory C fibers releases calcitonin gene-related peptide (CGRP), which increases heart rate, contractility, and coronary flow. C-fiber endings are closely associated with mast cells, and CGRP may release mast-cell histamine. Because prejunctional histamine H3-receptors inhibit transmitter release from autonomic nerves, we tested the hypothesis that H3-receptors modulate CGRP release in the heart. CGRP released by bradykinin in the electrically paced guinea pig left atrium and by capsaicin in the spontaneously beating isolated heart caused marked positive inotropic and chronotropic effects, respectively. Capsaicin significantly enhanced the overflow of CGRP (fivefold) and histamine (twofold) into the coronary effluent. All of these effects were prevented by prior chemical destruction of C fibers in vivo. The H3-receptor agonist imetit attenuated the inotropic response to bradykinin by 50%. Imetit also decreased the capsaicin-induced tachycardia and the increase in CGRP overflow by 50%. Imetit, however, did not modify the response to exogenous CGRP. The effects of imetit were blocked by the H3-receptor antagonist thioperamide. Notably, thioperamide by itself potentiated the capsaicin-evoked increases in heart rate and CGRP overflow (by 25% and 50%, respectively). Thus, our findings identify a negative-feedback loop, whereby CGRP releases histamine from cardiac mast cells and histamine in turn inhibits CGRP releases by activating H3-receptors on C-fiber terminals. Because CGRP release is augmented in pathophysiological conditions, such as septic shock, heart failure, and acute myocardial infarction, modulation of CGRP release may be clinically relevant.     

Release and clearance rates of epinephrine in man: importance of arterial measurements

Previous estimates of catecholamine kinetics in human subjects have been based on the measurement of the catecholamine levels in forearm venous plasma. However, the use of forearm venous measurements may introduce considerable error, since venous catecholamine levels may primarily reflect metabolism in the organ drained rather than in the total body. In this study, arterial levels of epinephrine were found to significantly exceed forearm venous levels, both basally (mean +/- SEM, 71 +/- 13 vs. 50 +/- 7 pg/ml; n = 6; P less than 0.05) and during infusions of epinephrine [0.1 microgram/min (112 +/- 9 vs. 77 +/- 11 pg/ml; P less than 0.005) or 2 micrograms/min (862 +/- 71 vs. 437 +/- 66 pg/ml; P less than 0.001)]. During the 2 micrograms/min epinephrine infusion, arterial plasma norepinephrine rose from 191 +/- 37 to 386 +/- 78 pg/ml (P less than 0.001), while venous norepinephrine levels did not change significantly. Fractional extraction (arterial - venous + arterial X 100) of epinephrine across the forearm was 26 +/- 8% in the basal state and increased to 33 +/- 6% and further to 51 +/- 4% during the epinephrine infusions. The addition of propranolol (5 mg, iv, plus an 80 micrograms/min infusion) reduced fractional extraction from 51 +/- 4% to 35 +/- 5%. Whole body clearance of epinephrine, calculated from arterial measurements, was 33 +/- 3 ml/kg . min during the 0.1 microgram/min infusion and 35 +/- 3 ml/kg . min during the 2 micrograms/min epinephrine infusion, values 50% lower than the clearance rates calculated from venous measurements. Propranolol infusion resulted in a fall in whole body clearance to 20 +/- 2 ml/kg . min (P less than 0.001), suggesting that epinephrine clearance is partly dependent on a beta-adrenergic mechanism. Basal endogenous release rate (clearance X basal epinephrine level) was estimated to be approximately 0.18 microgram/min, a value much less than that reported in studies using venous measurements. We conclude that arterial rather than venous measurements should be used to estimate catecholamine kinetics in vivo.     

Inhibition of sympathetic outflow by the angiotensin II receptor antagonist, eprosartan, but not by losartan, valsartan or irbesartan: relationship to differences in prejunctional angiotensin II receptor blockade

It is well established that angiotensin II can enhance sympathetic nervous system function by activating prejunctional angiotensin II type I (AT1) receptors located on sympathetic nerve terminals. Stimulation of these receptors enhances stimulus-evoked norepinephrine release, leading to increased activation of vascular alpha 1-adrenoceptors and consequently to enhanced vasoconstriction. In the present study, the effects of several chemically distinct nonpeptide angiotensin II receptor antagonists were evaluated on pressor responses evoked by activation of sympathetic outflow through spinal cord stimulation in the pithed rat. Stimulation of thoracolumbar sympathetic outflow in pithed rats produced frequency-dependent pressor responses. Infusion of sub-pressor doses of angiotensin II (40 ng/kg/min) shifted leftward the frequency-response curves for increases in blood pressure, indicating augmented sympathetic outflow. Furthermore, pressor responses resulting in spinal cord stimulation were inhibited by the peptide angiotensin II receptor antagonist, Sar1, Ile8 [angiotensin II] (10 micrograms/kg/min). These results confirm the existence of prejunctional angiotensin II receptors at the vascular neuroeffector junction that facilitate release of norepinephrine. The nonpeptide angiotensin II receptor antagonist, eprosartan (0.3 mg/kg i.v.), inhibited the pressor response induced by spinal cord stimulation in a manner similar to that observed with the peptide antagonist, Sar1, Ile8[angiotensin II]. In contrast, equivalent doses (0.3 mg/kg i.v.) of other nonpeptide angiotensin II receptor antagonists, such as losartan, valsartan, and irbesartan, had no effect on spinal cord stimulation of sympathetic outflow in the pithed rat. Although the mechanism by which eprosartan, but not the other nonpeptide angiotensin II receptor antagonists, inhibits sympathetic outflow in the pithed rat is unknown, one possibility is that eprosartan is a more effective antagonist of prejunctional angiotensin II receptors that augment neurotransmitter release. Because eprosartan is more effective in inhibiting sympathetic nervous system activity compared to other chemically distinct nonpeptide angiotensin II receptor antagonists, eprosartan may be more effective in lowering systolic blood pressure and in treating isolated systolic hypertension.     

Corticotropin-releasing factor administered centrally, but not peripherally, stimulates hippocampal acetylcholine release

In addition to corticotropin-releasing factor's well-known role in mediating hormonal and behavioral responses to stress, this peptide also reportedly affects arousal and cognition, processes that classically have been associated with forebrain cholinergic systems. Corticotropin-releasing factor stimulation of cholinergic neurons might thus provide a mechanism for this peptide's cognitive effects. To examine this possibility, the present experiments characterize the effect of corticotropin-releasing factor on cholinergic neurotransmission, using in vivo microdialysis to measure hippocampal acetylcholine release. Corticotropin-releasing factor (0.5-5.0 microg/rat intracerebroventricularly) was found to increase dialysate concentrations of acetylcholine in a dose-dependent manner in comparison with a control injection, the ovine peptide having a greater effect than the same dose of the human/rat peptide. This effect was found to be centrally mediated, independent of the peripheral effects of an exogenous corticotropin-releasing factor injection; subcutaneous injections of the peptide increased plasma concentrations of corticosterone, the adrenal hormone ultimately secreted in the rat's stress response, to the same level as did the central injections, without affecting hippocampal acetylcholine release. These results demonstrate that corticotropin-releasing factor, acting centrally, regulates hippocampal cholinergic activity, and suggest that corticotropin-releasing factor/acetylcholine interactions may underlie some of the previously identified roles of these neurotransmitters in arousal, cognition, and stress.     

Histamine potently suppresses human IL-12 and stimulates IL-10 production via H2 receptors

IL-12 and IL-10, respectively, stimulate Th1 and Th2 immune responses. The development of some allergic reactions, infections, and tumors are associated with excessive histamine production and a shift toward Th2 responses. Here we address the possibility that this association is causally linked, at least in part, to modulation of IL-12 and IL-10 production by histamine. We report that histamine dose-dependently inhibited the secretion of human IL-12 (p70) and increased the production of IL-10 in LPS-stimulated whole blood cultures. These effects of histamine were antagonized by cimetidine, an H2 receptor antagonist, but not by selective H1 and H3 receptor blockers, and were mimicked by an H2 receptor agonist. The effects of histamine on IL-12 and IL-10 secretion were independent of endogenous secretion of IL-10 or exogenous addition of IL-12, while Ro 20-1724, a phosphodiesterase inhibitor, potentiated the effects of histamine on IL-12 and IL-10 production, implicating cAMP in its actions. Similar modulatory effects of histamine on IL-12 and IL-10 production, which were reversed by the H2 antagonist cimetidine, were observed in PBMC and isolated monocytes stimulated by Staphylococcus aureus Cowan strain 1 and LPS, respectively. Thus, histamine, via stimulation of H2 receptors on peripheral monocytes and subsequent elevation of cAMP, suppresses IL-12 and stimulates IL-10 secretion, changes that may result in a shift of Th1/Th2 balance toward Th2-dominance. This may represent a novel mechanism by which excessive secretion of histamine potentiates Th2-mediated allergic reactions and contributes to the development of certain infections and tumors normally eliminated by Th1-dependent immune mechanisms.     

Mononuclear-cell peptide mediation of chromaffin-cell epinephrine secretion

Previously, we have shown that novel mononuclear-cell-derived factor(s) [molecular weight (MW) < 3,000] stimulate the release of epinephrine (EPI) from adrenal medullary chromaffin cells to levels comparable to that of maximal cholinergic stimulation. The present study provides evidence that the observed bioactivity is due to the action of a single peptide of 627 Da apparent MW. The peptide nature of the bioactive component was suggested by a decreased bioactivity after acid hydrolysis as well as altered bioactivity subsequent to peptidase (carboxypeptidase Y, leucine aminopeptidase) treatment. The bioactive conditioned-medium (CM) peptide(s) were isolated and further characterized using SDS-PAGE analysis. SDS-PAGE separation of G-25 Sephadex purified CM shows that bioactivity resides in a single peptide band. Additional studies revealed that CM also mediates norepinephrine release from sympathetic ganglia cells. Regulation of peptide production was shown to involve negative feedback in that incubation with mononuclear cells with EPI prevented further bioactive peptide release. This feedback inhibition was partially blocked by the beta-adrenergic receptor antagonist propranolol. These findings suggest a novel and potentially important mechanism by which the immune system can alter neuroendocrine function.     

Principal modifications of the Duhamel procedure in the treatment of Hirschsprung''s disease. Analysis based on results of an international retrospective study of 2,430 patients

The present study was undertaken to investigate the effects of losartan, a non-peptide angiotensin II subtype 1 (AT1) receptor antagonist, on both the pressor responses elicited by stimulation of afferent vagal nociceptive fibres and the involvement of the sympathetic nervous system (evaluated by plasma levels of noradrenaline and its co-neurotransmitter neuropeptide Y) in dogs. Electrical stimulation of the afferent fibres of the vagus (1, 5, 10 and 20 Hz) elicited a frequency-dependent increase in blood pressure and heart rate. Plasma noradrenaline levels only increased after stimulation at frequencies of 10 and 20 Hz. Plasma neuropeptide Y levels did not change. Losartan (10 mg/kg i.v.) induced both a decrease in resting blood pressure and an increase in basal plasma levels of noradrenaline and neuropeptide Y. Losartan failed to modify the magnitude of the electrically-evoked pressor and positive chronotropic responses. The angiotensin AT1 receptor antagonist elicited a fall in plasma noradrenaline values after a 1 Hz stimulation and abolished the increase in plasma noradrenaline levels induced by the 10 (but not 20) Hz stimulation. The data suggest that angiotensin AT1 receptors are not directly involved in acute pressor responses induced by stimulation of afferent vagal fibres. Moreover, the results show that, besides its sympatho-inhibitory effect, losartan can exert a sympatho-excitatory action as shown by the increase in the plasma levels of both noradrenaline and its coneurotransmitter, neuropeptide Y.