Neuropeptide Y stimulates bile secretion via Y1 receptor in the left dorsal vagal complex in rats

Obstructive jaundice activates nitroxidergic neurons of the vago-vagal neural circuit that regulates the hepatobiliary system in rabbits

In this study, we investigated the expression of neuronal nitric oxide synthase (nNOS) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d), two specific enzymes for nitric oxide (NO) synthesis, in the development of liver fibrosis induced by chronic bile duct ligation (BDL) in the rabbit. We specifically studied the liver-innervated nitroxidergic neurons that originate in the nodose ganglion (NG), nucleus of the solitary tract (NTS) and dorsal motor vagal nucleus (DMV). Our data showed that BDL resulted in overexpression of NADPH-d/nNOS in the NG, NTS and DMV neurons. Using densitometric analysis, we found a significant increase in NADPH-d expression as a result of BDL in the NG, NTS and DMV (72.6, 79.4 and 57.4% increase, respectively). These findings were corroborated by serum biochemistry and hepatic histopathological examination, which were influenced by NADPH-d/nNOS-generated NO in the liver following BDL. Upregulation of NADPH-d/nNOS expression may have important implications, including (1) facilitation of extrahepatic biliary parasympathetic tone that promotes gallbladder emptying of excess stagnant bile; (2) relaxation of smooth muscles of bile canaliculi thus participating in the pathogenesis of cholestasis; (3) dilation of hepatic sinusoids to counter BDL-induced intrahepatic portal hypertension in which endothelia may be damaged, and (4) alterations in hepatic metabolism, such as glycogenesis, bile formation and secretion, and bilirubin clearance.

β-Adrenoceptor blockade in sclerosing cholangitis of Mdr2 knockout mice: antifibrotic effects in a model of nonsinusoidal fibrosis

Primary sclerosing cholangitis (PSC) is a cholestatic liver disease with high propensity to develop into cholangiocarcinoma. The hepatobiliary disorder of PSC is due to progressive fibrosis surrounding the intra- and extrahepatic bile ducts. Until now, no effective medical therapy exists. To study the progression of sclerosing cholangitis after inhibition of the sympathetic nervous system by blockade of the β-adrenoceptors, we used the Mdr2(-/-) mouse model, which develops periportal fibrosis similar to human PSC. Liver tissues of Mdr2(-/-) mice untreated or treated with the β-adrenoceptor antagonist propranolol were analyzed for inflammation and fibrosis progression at different time points by histological scoring and immunostaining for α-smooth muscle actin (α-SMA), CD45 and S100A4. Transaminases and hydroxyproline contents were determined. Expression of angiotensinogen, endothelin-1, TGF-β, TNF-α, CTGF and procollagen 1A1 was studied by real-time PCR on laser-microdissected areas of acinar zones I and II-III. After 3 months, periportal fibrosis had developed in Mdr2(-/-) mice, but immunostaining revealed no sinusoidal and only minor periportal contribution of myofibroblasts with prominent fibroblasts. Propranolol treatment of Mdr2(-/-) mice improved liver architecture. Additionally, inflammation and fibrosis were significantly reduced. After 3 months of treatment, the antifibrotic effect of the β-blockade was most obvious. The transcript levels of procollagen 1A1, TNF-α, TGF-β, CTGF and endothelin-1 were markedly repressed in the portal areas of treated mice. Taken together, these data show that propranolol efficiently delays progression of sclerosing cholangitis. Therefore, the blockade of β-adrenoceptors is a promising option to support future therapeutic strategies in the treatment of human PSC.

The alpha2-adrenergic receptor agonist UK 14,304 inhibits secretin-stimulated ductal secretion by downregulation of the cAMP system in bile duct-ligated rats

Secretin stimulates ductal secretion by activation of cAMP --> PKA --> CFTR --> Cl(-)/HCO(3)(-) exchanger in cholangiocytes. We evaluated the expression of alpha(2A)-, alpha(2B)-, and alpha(2C)-adrenergic receptors in cholangiocytes and the effects of the selective alpha(2)-adrenergic agonist UK 14,304, on basal and secretin-stimulated ductal secretion. In normal rats, we evaluated the effect of UK 14,304 on bile and bicarbonate secretion. In bile duct-ligated (BDL) rats, we evaluated the effect of UK 14,304 on basal and secretin-stimulated 1) bile and bicarbonate secretion; 2) duct secretion in intrahepatic bile duct units (IBDU) in the absence or presence of 5-(N-ethyl-N-isopropyl)amiloride (EIPA), an inhibitor of the Na(+)/H(+) exchanger isoform NHE3; and 3) cAMP levels, PKA activity, Cl(-) efflux, and Cl(-)/HCO(3)(-) exchanger activity in purified cholangiocytes. alpha(2)-Adrenergic receptors were expressed by all cholangiocytes in normal and BDL liver sections. UK 14,304 did not change bile and bicarbonate secretion of normal rats. In BDL rats, UK 14,304 inhibited secretin-stimulated 1) bile and bicarbonate secretion, 2) expansion of IBDU luminal spaces, and 3) cAMP levels, PKA activity, Cl(-) efflux, and Cl(-)/HCO(3)(-) exchanger activity in cholangiocytes. There was decreased lumen size after removal of secretin in IBDU pretreated with UK 14,304. In IBDU pretreated with EIPA, there was no significant decrease in luminal space after removal of secretin in either the absence or presence of UK 14,304. The inhibitory effect of UK 14,304 on ductal secretion is not mediated by the apical cholangiocyte NHE3. alpha(2)-Adrenergic receptors play a role in counterregulating enhanced ductal secretion associated with cholangiocyte proliferation in chronic cholestatic liver diseases.

Control of hepatocyte metabolism by sympathetic and parasympathetic hepatic nerves

More than any other organ, the liver contributes to maintaining metabolic equilibrium of the body, most importantly of glucose homeostasis. It can store or release large quantities of glucose according to changing demands. This homeostasis is controlled by circulating hormones and direct innervation of the liver by autonomous hepatic nerves. Sympathetic hepatic nerves can increase hepatic glucose output; they appear, however, to contribute little to the stimulation of hepatic glucose output under physiological conditions. Parasympathetic hepatic nerves potentiate the insulin-dependent hepatic glucose extraction when a portal glucose sensor detects prandial glucose delivery from the gut. In addition, they might coordinate the hepatic and extrahepatic glucose utilization to prevent hypoglycemia and, at the same time, warrant efficient disposal of excess glucose.

Selective activation of central NPY Y1 vs. Y5 receptor elicits hyperinsulinemia via distinct mechanisms

Central administration of neuropeptide Y (NPY) stimulates hyperphagia and hyperinsulinemia. Recent evidence has suggested that the Y1 and Y5 receptor subtypes may both mediate NPY-stimulated feeding. The present study attempts to further characterize the role of central NPY receptor subtypes involved in hyperinsulinemia. NPY and peptide analogs of NPY that selectively activated the NPY Y1 or Y5 receptor subtype induced feeding and hyperinsulinemia in satiated Long Evans rats, whereas NPY analogs that selectively activated the NPY Y2 or Y4 receptor subtype did not. To determine whether NPY-induced hyperinsulinemia is secondary to its hyperphagic effect, we compared the plasma insulin levels in the presence and absence of food after a 1-min central infusion of NPY and its analogs at 15, 60, and 120 min postinfusion. Our data suggest that selective activation of central NPY Y1 receptor subtype induced hyperinsulinemia independent of food ingestion, whereas the NPY Y5 receptor-induced hyperinsulinemia was dependent on food ingestion. Central administration of the selective Y1 receptor agonist D-Arg25 NPY eventually decreased plasma glucose levels 2 h postinfusion in Long Evans rats.

Thyrotropin-releasing hormone in the dorsal vagal complex stimulates hepatic blood flow in rats

Central administration of thyrotropin-releasing hormone (TRH) enhances hepatic blood flow in animal models. TRH nerve fibers and receptors are localized in the dorsal vagal complex (DVC), and retrograde tracing techniques have shown that hepatic vagal nerves arise mainly from the left DVC. However, nothing is known about the central sites of action for TRH to elicit the stimulation of hepatic blood flow. The effect of microinjection of a TRH analogue into the DVC on hepatic blood flow was investigated in urethane-anesthetized rats. After measuring basal flow, a stable TRH analogue (RX-77368) was microinjected into the DVC and hepatic blood flow response was observed for 120 minutes by laser Doppler flowmetry. Either left or right cervical vagotomy or hepatic branch vagotomy was performed 2 hours before the peptide. Microinjection of RX-77368 (0.5-5 ng) into the left DVC dose-dependently increased hepatic blood flow. The stimulation of hepatic blood flow by RX-77368 microinjection into the left DVC was eliminated by left cervical and hepatic branch vagotomy but not by right cervical vagotomy. By contrast, microinjection of RX-77368 into the right DVC did not significantly alter hepatic blood flow. These results suggest that TRH acts in the left DVC to stimulate hepatic blood flow through the left cervical and hepatic vagus, indicating that neuropeptides may act in the specific brain nuclei to regulate hepatic function.

Stimulation of neurons in rat ARC inhibits gastric acid secretion via hypothalamic CRF1/2- and NPY-Y1 receptors

Neuropeptide Y (NPY) neuronal projections from the arcuate nucleus (ARC) have been proposed to target corticotropin-releasing factor (CRF)-positive neurons in the paraventricular nucleus (PVN) as part of the ARC-PVN axis. The existence of a positive feedback loop involving CRF receptors in the PVN has been suggested. Exogenous NPY and CRF in the PVN have been shown to inhibit gastric acid secretion. Recently, we have demonstrated that activation of ARC neurons inhibits gastric acid secretion via vagal pathways. To what extent NPY- and CRF-mediated mechanisms in the PVN contribute to the CNS modulation of gastric acid secretion is still an open question. In the present study, we performed consecutive bilateral microinjections of antagonists to NPY receptor subtypes Y1 and Y2 and to CRF1/2 receptors in the PVN and of the excitatory amino acid kainate in the ARC to assess the role of NPY- and CRF-mediated mechanisms in the kainate-induced effects on gastric acid secretion. Gastric acid secretion was measured at the basal condition and during pentagastrin (16 microg/kg body wt) stimulation. Microinjection of vehicle in the PVN and kainate in the ARC decreased gastric acid secretion. Microinjection of the specific NPY-Y1 receptor antagonist BIBP-3226 (200 pmol) and the nonspecific CRF1/2 antagonist astressin (30 pmol) in the PVN abolished the inhibitory effect of neuronal activation in the ARC by kainate on gastric acid secretion. The CRF antagonist astressin was more effective. Pretreatment with the NPY-Y2 receptor antagonist BIIE-0246 (120 pmol) in the PVN had no significant effect. Our results indicate that activation of neurons in the ARC inhibits gastric acid secretion via CRF1/2 and NPY-Y1 receptor-mediated pathways in the PVN.

Lafutidine increases hepatic blood flow via potentiating the action of central thyrotropin-releasing hormone in rats

BACKGROUND

Lafutidine, (+/-)-2-(furfurylsulfinyl)-N-[4-[4-(piperidinomethyl)-2-pyridyl]oxy-(Z)-2 butenyl]acetamide, is a newly synthesized histamine H2 receptor antagonist and possesses a cytoprotective efficacy, which comprises mucin biosynthesis and stimulation of gastric blood flow mediated through capsaicin-sensitive sensory neurons and endogenous calcitonin gene-related peptide (CGRP). In the present study, an effect of lafutidine on hepatic blood flow was investigated in rats that received an intracisternal injection of a subthreshold dose of thyrotropin-releasing hormone (TRH) analog, RX 77368.

METHODS

Change in hepatic blood flow was determined by laser Doppler flowmetry. Male Wistar rats were anesthetized with urethane (1.5 g/kg, i.p.), and positioned on a stereotaxic apparatus. An abdominal incision was made, and a probe of laser Doppler flowmeter was placed on the surface of the liver. After a 60-min stabilization, basal hepatic blood flow was measured for 30 min, and lafutidine (0.5, 1, 3, 5 or 10 mg/kg) or vehicle was injected into the portal vein and a subthreshold dose (1.5 ng) of RX 77368 was injected intracisternally. Hepatic blood flow was monitored for 120 min postinjection. To investigate a role of capsaicin-sensitive sensory neurons and endogenous CGRP, systemic capsaicin treatment (125 mg/kg, s.c., 10-14 days before) and intravenous infusion of a CGRP receptor antagonist, human CGRP-(8-37) (15 micro g/kg as a bolus, followed by infusion at 3 micro g/kg/h) were performed, respectively.

RESULTS

Intracisternal injection of RX 77368 (1.5 ng) or intraportal lafutidine (10 mg/kg) by itself did not affect hepatic blood flow, but co-injection of intracisternal RX 77368 (1.5 ng) and intraportal lafutidine (5 mg/kg) increased it with peak response at 30 min postinjection. The effect of lafutidine on hepatic blood flow in rats given RX 77368 was dose-related over the range 1-5 mg/kg. By contrast, intracisternal injection of RX 77368 (1.5 ng) did not change hepatic blood flow in rats injected with another histamine H2 receptor antagonist, famotidine (5 mg/kg), intraportally. The stimulatory effect of co-injection of TRH analog and lafutidine was abolished by systemic capsaicin-treatment and CGRP antagonist.

CONCLUSION

These data suggest that lafutidine increases hepatic blood flow by sensitizing the liver to the action of central TRH via both capsaicin-sensitive sensory neurons and endogenous CGRP in urethane-anesthetized rats.

Gastric protective effect of peripheral PYY through PYY preferring receptors in anesthetized rats

The influence of intravenous peptide YY (PYY) on the gastric injury induced by 45% ethanol was investigated in urethane-anesthetized rats. PYY (25, 75, 125, and 250 pmol x kg(-1) x h(-1)) significantly reduced gastric lesions by 36, 59, 40, and 38%, respectively. Antibody against ratPYY (2 mg/rat) injected intravenously completely prevented the gastroprotective effect of intravenous PYY (75 pmol x kg(-1) x h(-1)), whereas injected intracisternally (460 microg/20 microl), it significantly prevented intracisternal PYY (24 pmol/rat)-induced 58% reduction of ethanol lesions but not that induced by intravenous PYY. Vagotomy did not influence the gastroprotective effect of intravenous PYY. The Y(1)/"PYY-preferring" receptor agonist [Pro(34)]PYY (75 pmol x kg(-1) x h(-1) iv) significantly decreased ethanol-induced gastric lesions by 82%, whereas [Leu(31), Pro(34)]NPY, a Y(1)/Y(3) agonist, and PYY-(3-36), a Y(2) agonist, had no effect. These data indicate that PYY-infused intravenously at doses reported to mimic postprandial peak blood levels prevents ethanol-induced gastric injury through vagal independent pathways and PYY-preferring receptors.

Involvement of endogenous CRF in carbon tetrachloride-induced acute liver injury in rats

Central neuropeptides play important roles in many physiological and pathophysiological regulation mediated through the autonomic nervous system. In regard to the hepatobiliary system, several neuropeptides act in the brain to regulate bile secretion, hepatic blood flow, and hepatic proliferation. Central injection of corticotropin-releasing factor (CRF) aggravates carbon tetrachloride (CCl4)-induced acute liver injury through the sympathetic nervous pathway in rats. However, still nothing is known about a role of endogenous neuropeptides in the brain in hepatic pathophysiological regulations. Involvement of endogenous CRF in the brain in CCl4-induced acute liver injury was investigated by centrally injecting a CRF receptor antagonist in rats. Male fasted Wistar rats were injected with CRF receptor antagonist alpha-helical CRF-(9-41) (0.125-5 microg) intracisternally just before and 6 h after CCl4 (2 ml/kg) administration, and blood samples were obtained before and 24 h after CCl4 injection for measurement of hepatic enzymes. The liver sample was removed 24 h after CCl4 injection, and histological changes were examined. Intracisternal alpha-helical CRF-(9-41) dose dependently (0.25-2 microg) reduced the elevation of alanine aminotransferase and aspartate aminotransferase levels induced by CCl4. Intracisternal alpha-helical CRF-(9-41) reduced CCl4-induced liver histological changes, such as centrilobular necrosis. The effect of central CRF receptor antagonist on CCl4-induced liver injury was abolished by sympathectomy and 6-hydroxydopamine pretreatment but not by hepatic branch vagotomy or atropine pretreatment. These findings suggest the regulatory role of endogenous CRF in the brain in experimental liver injury in rats.

Central and peripheral regulation of gastric acid secretion by peptide YY

Peptide YY (PYY) released postprandially from the ileum and colon displays a potent inhibition of cephalic and gastric phases of gastric acid secretion through both central and peripheral mechanisms. To modulate vagal regulation of gastric functions, circulating PYY enters the brain through the area postrema and the nucleus of the solitary tract, where it exerts a stimulatory action through PYY-preferring Y1-like receptors, and an inhibitory action through Y2 receptors. In the gastric mucosa, PYY binds to Y1 receptors in the enterochromaffin-like cells to inhibit gastrin-stimulated histamine release and calcium signaling via a pertussis toxin-sensitive pathway.

Centrally administered neuropeptide Y delays gastric emptying via Y2 receptors in rats

It has been shown that centrally administered neuropeptide Y (NPY) delays gastric emptying. To determine the receptor subtypes of NPY mediating the inhibitory effects on gastric emptying, effects of intracerebroventricular injection of NPY, [Leu31,Pro34]NPY (a Y1 agonist) and NPY-(3-36) (a Y2 agonist) on solid gastric emptying and postprandial antropyloric motility were studied in conscious rats. Intracerebroventricular injection of NPY and NPY-(3-36), but not [Leu31,Pro34] NPY, delayed solid gastric emptying in a dose-dependent manner (0.03-3 nmol). After the feeding (40 min), contractions with low frequency and high amplitude of the antrum were frequently observed, and the peak contraction of the antrum occurred most often 3-6 s before the peak contraction of the pylorus. Intracerebroventricular injection of NPY and NPY-(3-36) (3 nmol), but not [Leu31,Pro34]NPY, significantly reduced antral contractions and the number of antropyloric coordination events. It is suggested that centrally administered NPY impairs postprandial antral contractions and antropyloric coordination via Y2 receptors, resulting in delayed gastric emptying.

Excitatory stimulation of neurons in the arcuate nucleus inhibits gastric acid secretion via vagal pathways in anesthetized rats

It is well established that autonomic control of gastrointestinal function is modulated by central autonomic neurotransmission. In this context it has been shown that gastrointestinal motility and secretion can be modulated by exogenous neuropeptides microinjected into the paraventricular nucleus of the hypothalamus (PVN). Furthermore, there is considerable evidence suggesting that neurons projecting from the arcuate nucleus (Arc) to the PVN may be the source of endogenous neuropeptide release in the PVN. This poses the question whether stimulation of neurons in the arcuate nucleus, e.g. by an excitatory amino acid, alters gastrointestinal function. In the present study, we investigated the effect of an excitatory amino acid, kainate, microinjected into the arcuate nucleus on gastric acid secretion in urethane-anesthetized rats. Kainate (140 pmol/rat) bilaterally microinjected into the Arc induced an significant inhibition of pentagastrin (PG) stimulated (16 mg/kg per h) gastric acid secretion throughout an observation period of 120 min after microinjection. Microinjection of kainate into hypothalamic areas outside the arcuate nucleus did not modify gastric secretion. Bilateral cervical vagotomy blocked the effect of kainate injected into the Arc on PG-stimulated gastric acid secretion. These data show that gastric secretory function can be modulated by stimulation of neuronal activity in the Arc via efferent vagal pathways. The results suggest that the arcuate nucleus is a forebrain area involved in the CNS regulation of gastrointestinal function.

Gastric distension-induced pyloric relaxation: central nervous system regulation and effects of acute hyperglycaemia in the rat

1. The pylorus plays an important role in the regulation of gastric emptying. In addition to the autonomic neuropathy associated with long-standing diabetes, acute hyperglycaemia per se has effects on gastric emptying. In this study, the role of the central nervous system in modulating the effects of hyperglycaemia on gastric distension-induced pyloric relaxation was investigated. 2. Gastric distension-induced pyloric relaxation was significantly reduced by subdiaphragmatic vagotomy, hexamethonium (20 mg kg(-1)) and N (G)-nitro-L-arginine methyl ester (L-NAME; 10 mg kg(-1)), a nitric oxide synthase (NOS) biosynthesis inhibitor, in anaesthetized rats. In contrast, neither splanchnectomy nor guanethidine (5 mg kg(-1)) had an effect. 3. An intravenous (I.V.) infusion of D-glucose (20 %) for 30 min, which increased blood glucose concentrations from 5.4 to 12.8 mM, significantly inhibited gastric distension-induced pyloric relaxation. 4. An intracerebroventricular (I.C.V.) injection of D-glucose (3 micromol) also significantly inhibited gastric distension-induced pyloric relaxation without affecting peripheral blood glucose concentrations. 5. I.V. infusion of D-glucose significantly elevated hypothalamic neuropeptide Y (NPY) concentrations. 6. Intracerebroventricular (I.C.V.) administration of NPY (0.03--3 nmol) and a Y1 receptor agonist, [leu(31), pro(34)] NPY (0.03--3 nmol), significantly inhibited gastric distension-induced pyloric relaxation in a dose-dependent manner. 7. I.C.V. administration of a Y1 receptor antagonist, BIBP 3226 (30 nmol), and of a NPY antibody (titre 1:24 000, 3 microl) abolished the inhibitory effects of hyperglycaemia on gastric distension-induced pyloric relaxation. 8. Taken together, these findings suggest that gastric distension-induced pyloric relaxation is mediated via a vago-vagal reflex and NO release. Acute hyperglycaemia stimulates hypothalamic NPY release, which, acting through the Y1 receptor, inhibits gastric distension-induced pyloric relaxation in rats exposed to acute elevations in blood glucose concentrations.

Vagal circuitry mediating cephalic-phase responses to food

The dorsal vagal complex in the medulla oblongata is the hub of the central nervous system network that produces vagal cephalic-phase reflexes. The preganglionic motor neurons controlling these cephalic responses of digestion and metabolism are organized topographically in longitudinal columnar subnuclei in the dorsal motor nucleus of the vagus. Gustatory and other visceral afferent inputs project into different subnuclei of the nucleus of the solitary tract capping the dorsal motor nucleus. Descending projections from more rostral stations of the neuroaxis project to the nuclei of the dorsal vagal complex, providing input both from exteroceptive senses, such as olfaction and vision, and from forebrain areas that modulate reflex strength. Recent structural analyses of the dorsal vagal complex, as well as characterizations of the region's inputs and neurochemistry, have provided a more complete understanding of the neural basis of cephalic-phase responses.

Role of calcitonin gene-related peptide and capsaicin-sensitive afferents in central thyrotropin-releasing hormone-induced hepatic hyperemia

The involvement of capsaicin-sensitive afferent neurons and calcitonin gene-related peptide (CGRP) in the central thyrotropin-releasing hormone (TRH)-induced hepatic hyperemia was investigated in urethane anesthetized rats. Both systemic capsaicin pretreatment and intravenous administration of CGRP receptor antagonist, human CGRP-(8-37), completely abolished the stimulatory effect of hepatic blood flow induced by intracisternal injection of TRH analog (RX-77368; p-Glu-His-(3,3'-dimethyl)-Pro-NH2, 100 ng), assessed by the hydrogen gas clearance method. These data demonstrate the involvement of capsaicin-sensitive afferent neurons and CGRP in the central TRH-induced stimulation of hepatic blood flow.

Biliary tract physiology

Largely because of the recent development of new experimental models, cholangiocytes--the cells lining the bile ducts--are now recognized as important contributors to and modulators of bile formation. Recent work elucidating the mechanisms and regulation of fluid, solute, and electrolyte transport indicates that the biliary epithelium influences bile formation through both autocrine and paracrine mechanisms. Novel roles for bile acids in cholangiocyte physiology have been proposed, and insight into the anatomic and functional differences of cholangiocytes along the biliary tree has been gained. Improved understanding of these concepts and the pathophysiologic response of the biliary tree to injury should provide new therapies for biliary diseases.

Intracisternal PYY increases gastric mucosal resistance: role of cholinergic, CGRP, and NO pathways

The influence of intracisternal injection of peptide YY (PYY) on gastric lesions induced by ethanol was studied in urethan-anesthetized rats. Gastric lesions covered 15-22% of the corpus as monitored 1 h after intragastric administration of 45% ethanol (5 ml/kg) in intracisternal vehicle control groups. PYY, at doses of 23, 47, or 117 pmol 30 min before ethanol, decreased gastric lesions by 27%, 63%, and 59%, respectively. Thyrotropin-releasing hormone (TRH) receptor antisense oligodeoxynucleotide pretreatment (intracisternally, 48 and 24 h before intracisternal PYY) did not influence the gastroprotective effect of intracisternal PYY (47 pmol) but abolished that of intracisternal TRH analog RX-77368 (4 pmol). RX-77368 (2.6 pmol) and PYY (6 pmol) were ineffective when injected intracisternally alone but reduced ethanol lesions by 44% when injected simultaneously. Atropine (subcutaneously), the calcitonin gene-related peptide (CGRP) receptor antagonist CGRP-(8-37) (intravenously), or the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, intravenously) completely abolished the gastroprotective effect of intracisternal PYY (47 pmol), whereas indomethacin (intraperitoneally) had no effect. The L-NAME action was reversed by L-arginine but not by D-arginine (intravenously). These results suggest that intracisternal PYY acts independently of medullary TRH to decrease ethanol-induced gastric lesions. The PYY action involves vagal cholinergic-mediated CGRP/NO protective mechanisms.

Effect of central corticotropin-releasing factor on carbon tetrachloride-induced acute liver injury in rats

Central neuropeptides play important roles in many instances of physiological and pathophysiological regulation mediated through the autonomic nervous system. In regard to the hepatobiliary system, several neuropeptides act in the brain to regulate bile secretion, hepatic blood flow, and hepatic proliferation. Stressors and sympathetic nerve activation are reported to exacerbate experimental liver injury. Some stressors are known to stimulate corticotropin-releasing factor (CRF) synthesis in the central nervous system and induce activation of sympathetic nerves in animal models. The effect of intracisternal CRF on carbon tetrachloride (CCl4)-induced acute liver injury was examined in rats. Intracisternal injection of CRF dose dependently enhanced elevation of the serum alanine aminotransferase (ALT) level induced by CCl4. Elevations of serum aspartate aminotransferase, alkaline phosphatase, and total bilirubin levels by CCl4 were also enhanced by intracisternal CRF injection. Intracisternal injection of CRF also aggravated CCl4-induced hepatic histological changes. Intracisternal CRF injection alone did not modify the serum ALT level. Intravenous administration of CRF did not influence CCl4-induced acute liver injury. The aggravating effect of central CRF on CCl4-induced acute liver injury was abolished by denervation of hepatic plexus with phenol and by denervation of noradrenergic fibers with 6-hydroxydopamine treatment but not by hepatic branch vagotomy or atropine treatment. These results suggest that CRF acts in the brain to exacerbate acute liver injury through the sympathetic-noradrenergic pathways.