Hyperdynamic circulation of cirrhotic rats: role of substance P and its relationship to nitric oxide

Ablation of primary afferent neurons by neonatal capsaicin treatment reduces the susceptibility of the portal hypertensive gastric mucosa to ethanol-induced injury in cirrhotic rats

Primary sensory afferent neurons modulate the hyperdynamic circulation in cirrhotic rats with portal hypertension. The stomach of cirrhotic rats is prone to damage induced by ethanol, a phenomenon associated with reduced gastric hyperemic response to acid-back diffusion. The aim of this study was to examine the impact of ablation of capsaicin-sensitive neurons and the tachykinin NK(1) receptor antagonist A5330 on the susceptibility of the portal hypertensive gastric mucosa to ethanol-induced injury and its effects on gastric cyclooxygenase (COX) and nitric oxide synthase (NOS) mRNA expression. Capsaicin was administered to neonatal, male, Wistar rats and the animals were allowed to grow. Cirrhosis was then induced by bile duct ligation in adult rats while controls had sham operation. Ethanol-induced gastric damage was assessed using ex vivo gastric chamber experiments. Gastric blood flow was measured as well as COX/NOS mRNA expression. Topical application of ethanol produced significant gastric damage in cirrhotic rats compared to controls, which was reversed in capsaicin- and A5330-treated animals. Mean arterial and portal pressure was normalized in capsaicin-treated cirrhotic rats. Capsaicin and A5330 administration restored gastric blood flow responses to topical application of ethanol followed by acid in cirrhotic rats. Differential COX and NOS mRNA expression was noted in bile duct ligated rats relative to controls. Capsaicin treatment significantly modified gastric eNOS/iNOS/COX-2 mRNA expression in cirrhotic rats. Capsaicin-sensitive neurons modulate the susceptibility of the portal hypertensive gastric mucosa to injury induced by ethanol via tachykinin NK(1) receptors and signalling of prostaglandin and NO production/release.

Hemodynamic effects of substance P and its receptor antagonist RP67580 in anesthetized rats with carbon tetrachloride-induced cirrhosis

OBJECTIVE

Substance P (SP) is a vasodilator that may contribute to systemic and splanchnic vasodilatation in cirrhosis. The aim of this study was to determine the effects of SP (dose--13 pg/kg) and its specific inhibitor, RP67580 (dose--300 microg/kg) on mean arterial pressure (MAP) and portal pressure (PP) in cirrhotic rats and controls.

MATERIAL AND METHODS

MAP and PP were measured before and after administering SP and RP67580. Additionally, a small group of cirrhotic rats were pretreated with L-NAME to block the effects of nitric oxide (NO) before measurements.

RESULTS

SP produced transient systemic hypotension in both groups. SP caused a significant increase in PP in cirrhotic rats and a decrease in PP in controls. RP67580 reduced the hypotensive effect of SP, but not completely. RP67580 decreased PP in the cirrhotic group but not in controls. In cirrhotic rats pretreated with L-NAME, SP administration caused a significant decrease in MAP but no significant change in PP.

CONCLUSIONS

Exogenous SP increases PP and decreases MAP in cirrhotic rats. RP687580 decreases PP and reduces SP-induced hypotension in cirrhotic rats. NO blockade abolishes the effect of SP on PP. SP contributes to splanchnic vasodilatation in cirrhosis and this effect may be mediated by NO.

Hemodynamic effects of one week of carvedilol administration on cirrhotic rats

BACKGROUND

Carvedilol is a nonselective beta-blocker with alpha(1)-adrenergic blocking activity. It has been shown to decrease portal pressure in cirrhotic patients. The current study was undertaken to evaluate the possible mechanism of carvedilol on hemodynamics in cirrhotic rats with portal hypertension produced by common bile duct ligation.

METHODS

Male Sprague-Dawley rats received either a sham operation or common bile duct ligation. Three weeks after surgery, both sham-operated and cirrhotic rats were randomly assigned to receive vehicle or carvedilol 5 mg.kg(-1).12 h(-1) by gastric gavage for 1 week. Hemodynamic measurements, serum biochemistry, serum nitrate/nitrite and 6-keto-PGF(1alpha) levels, and aortic mRNA expression of eNOS and COX-1 were performed on the eighth day after drug administration.

RESULTS

Carvedilol treatment did not affect serum biochemistry in either sham-operated or cirrhotic rats. In sham-operated rats, administration of carvedilol significantly decreased the heart rate without affecting other hemodynamic values. In contrast, in cirrhotic rats, administration of carvedilol significantly decreased the cardiac index, portal pressure, heart rate, and portal territory blood flow, and it significantly increased systemic and portal territory vascular resistances. The hepatocollateral resistance was significantly decreased, but the hepatic arterial blood showed no significant changes. In sham-operated rats treated with carvedilol, serum nitrate/nitrite and 6-keto-PGF(1alpha) levels were not affected. In contrast, cirrhotic rats receiving carvedilol showed a significant decrease in serum nitrate/nitrite and 6-keto-PGF(1alpha) levels, associated with a decrease in aortic mRNA expression of eNOS and COX-1 compared with those receiving vehicle.

CONCLUSIONS

Carvedilol decreased portal pressure through a reduction of splanchnic blood flow associated with a decrease in hepatocollateral resistance. Additionally, administration of carvedilol decreased endothelial-related vasodilatory activities.

Temporal decrease in renal sensory responses in rats after chronic ligation of the bile duct

Renal responses to renal sensory receptor activation were examined in rats after 1 and 4 wk of common bile duct ligation (CBDL). Compared with sham-operated rats (Sham), urine and sodium excretion after acute saline loading was significantly reduced at both times after CBDL. The blunted excretory responses in CBDL rats, accompanied by less activation of afferent renal nerve activity (ARNA), were already apparent at 1 wk and became severe at 4 wk. The defect in ARNA activation in CBDL rats was further studied using specific stimuli to activate renal sensory receptors. Graded increases in intrapelvic pressure or renal pelvic perfusion of substance P (SP) elicited an increase in ARNA in Sham rats, these responses being temporally attenuated in CBDL rats. Despite no significant change in renal pelvic SP release, no renorenal reflex was demonstrable in 4-wk CBDL rats. Immunoblotting showed that expression of renal pelvic neurokinin 1 (NK-1) receptors was 32 and 47% lower in 1- and 4-wk CBDL rats, respectively, than in Sham rats, this decrease correlating well with plasma SP levels. The quantitative real-time RT-PCR showed similar levels of NK-1 receptor mRNA in the renal pelvis in the Sham and 4-wk CBDL groups. We conclude that impairment of renal excretory and sensory responses increases with the duration of cirrhosis. An impaired renorenal reflex in cirrhotic rats is involved in the defective activation of the renal sensory receptors could be due, in part, to the low expression of NK-1 receptors, which is dependent on the duration of CBDL. The decrease in NK-1 receptor protein levels is not due to a decrease in mRNA levels.

Abamectin effects on aspartate aminotransferase and nitric oxide in rats

Abamectin is widely used as an insecticide and an anthelmintic. A previous report indicated that abamectin was used to commit suicide and led to death in Taiwan. This investigation focused on the toxicological effects of abamectin on serum aspartate aminotransferase (AST) and nitrate/nitrite (NO) levels in rats. After rats were gavaged with abamectin ranging from 1 to 20 mg/kg/body weight, AST and NO levels were examined within 12 h. AST and NO levels were elevated in abamectin-dosed rats in a dose-dependent manner. The least increase of AST corresponded to the highest enhancement of NO release at 6 h. A negative correlation coefficient (r=-0.55) between AST and NO was found. Both NG-nitro-L-arginine-methyl ester and aminoguanidine, inhibitors of nitric oxide synthase, increased the AST level induced by abamectin. These findings suggest that NO may be involved in the alteration of AST release induced by abamectin in rats.

Nitric oxide and the liver

In recent years, the role of nitric oxide (NO) in the pathogenesis of liver disease and its complications has been extensively studied. There remain, however, many areas of controversy. In particular, the effect of NO on vascular function in the systemic circulation and the hepatic microcirculation has received the greatest attention. It has been proposed on the one hand that increased NO synthesis is responsible for the development of the hyperdynamic circulation in cirrhosis, while decreased production of NO within the hepatic microcirculation may be important in the development of parenchymal tissue damage and the onset of portal hypertension. The purpose of this review is to examine the available data concerning the role of NO in liver disease and to discuss some of the controversies and contradictions that surround it.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).