Impaired Adaptive Cytoprotection to Ethanol-Induced Damage in Gastric Mucosa of Portal Hypertensive Rats

Portal hypertension predisposes gastric mucosato increased damage by noxious agents. Adaptivecytoprotection has not been studied in portalhypertensive gastric mucosa. We evaluated adaptivecytoprotection in the gastric mucosa of portal hypertensiverats by exposure to ethanol. The injury index (percentgross lesions) was significantly higher in portalhypertensive rats than in sham-operated rats. The ratio of adaptive cytoprotection, calculated as thedegree of decrease in the injury index caused bypre-absolute-ethanol administration of 20% ethanol, wassignificantly impaired in portal hypertensive rats. Basal levels of gastric mucosal hexosamine werelower in portal hypertensive rats than in controls, anda blunted response to 20% ethanol was associated withportal hypertension. Nitric oxide inhibition (L-NAME, 5 mg/kg) reduced the ratio of adaptivecytoprotection in sham-operated but not in portalhypertensive rats. These results suggest that impairedadaptive cytoprotection in portal hypertensive gastric mucosa may be caused by blunted mucusproduction.     

The role of epidermal growth factor in gastric epithelial proliferation in portal hypertensive rats exposed to stress

BACKGROUND/AIMS: This study was designed to determine whether epidermal growth factor may have a role in the stomach of portal hypertensive rats after exposure to water immersion and restraint stress. METHODOLOGY: Rats with portal hypertension (portal vein partial ligation) were studied to determine the proliferative response of the gastric epithelium to epidermal growth factor (EGF) during stress. The portal hypertensive rats received EGF (0, 10, 25, 50, and 100 microg/kg/day) subcutaneously for 7 days before water immersion restraint stress. Each rat was subjected to water immersion restraint stress for 6 hours, at the end of which the stomachs were excised to evaluate gross and microscopic mucosal damage, and gastric epithelial proliferation using proliferating cell nuclear antigen (PCNA) immunoreactivity. RESULTS: The gross and microscopic mucosal damage were significantly greater in control or low dose EGF-pretreated (10 or 25 microg/kg/day) rats than in high dose EGF-pretreated (50 or 100 microg/kg/day) rats (p<0.01). These changes were accompanied by parallel alterations in the PCNA labeling index. The PCNA labeling index between high dose EGF-pretreated and control or low dose EGF-pretreated rats differed significantly (p<0.01). CONCLUSIONS: This study clearly indicates that the influence of EGF on the proliferative response of the portal hypertensive (PHT) gastric epithelium to stress in rats was dose-dependent, suggesting an important role for EGF in the protection of PHT gastric mucosa from stress injury.     

Increased Gastric Bicarbonate Secretion in Portal Hypertensive Anesthetized Rats (Role of Prostaglandins and Nitric Oxide)

Gastric bicarbonate secretion might be modifiedin portal hypertension as a consequence of theintramucosal increase in prostaglandins and nitric oxidecontent. Therefore, we studied gastric bicarbonate secretion in control and portal hypertensiverats and investigated the role of prostaglandins andnitric oxide. Basal gastric bicarbonate secretion wasstudied in rats, using a gastric pH back-titration technique, two weeks after partial portal veinligation or a sham operation. The effects of thefollowing drugs were investigated: the prostaglandinsynthase inhibitor indomethacin (5 mg/kg intravenously), prostaglandin (PGE₂) (1 mg/kgintravenously), the nitric oxide synthase inhibitorsN^G-nitro-L-arginine methyl ester (LG NAME, 5mg/kg intravenously) andN^G-monomethyl-L-arginine (L-NMMA, 50 mg/kgintravenously), and the nitric oxide donor nitroprusside (5mmol/liter in the gastric perfusate). Plasma leakage inthe gastric wall was also measured after Evans blue dyeinjection in portal hypertensive and sham-operated rats pretreated by indomethacin (5 mg/kg,intravenously) and L-NAME (5 mg/kg, intravenously).Basal bicarbonate secretion was significantly increasedin portal hypertensive rats as compared to controls. After indomethacin, the bicarbonate secretionwas significantly reduced to a similar level in bothgroups. PGE₂ increased bicarbonate secretionsignificantly more in portal hypertensive rats than insham-operated rats. The NO synthase inhibitor L-NMMAsignificantly increased bicarbonate secretion in portalhypertensive rats only, while the other inhibitor,L-NAME, increased it significantly more in portalhypertensive than in the sham-operated rats. Plasma leakagein portal hypertensive rats, which was increased in thebasal condition as compared to control, was furtherenhanced by indomethacin but not by L-NAME pretreatment. The nitric oxide donor significantly reducedbicarbonate secretion in portal hypertensive rats toreach a similar level as in sham-operated rats. Basalgastric bicarbonate secretion is increased in portal hypertensive rats. This could be due to anenhanced prostaglandin mucosal level. Nitric oxide,which reduces bicarbonate secretion, may contribute tolimiting prostaglandin-induced bicarbonateoverproduction.     

Calcium antagonist inhibits glomerular cell apoptosis and injuries of L-NAME exacerbated nephrosclerosis in SHR.

Increased apoptosis of glomerular cells, with progression of glomerulosclerosis, overactivity of the renin-angiotensin system and elevation of glomerular pressure, follows chronic nitric oxide synthase (NOS) inhibition in spontaneously hypertensive rats (SHR). To gain insight into the regulation of glomerular cell apoptosis in severe nephrosclerosis, we investigated apoptosis, the expression of proliferative cell nuclear antigen (PCNA) in glomeruli, and glomerular morphometric changes in 20-week-old SHR, SHR treated with NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME; 80 mg/l in drinking water), and SHR treated with L-NAME and the calcium antagonist, efonidipine (20 mg/kg per day), for 3 weeks. Apoptosis in non-sclerotic glomeruli was quantified by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling. The increase in systolic blood pressure and the severe proteinuria with severe nephrosclerosis induced by chronic NOS inhibition were completely prevented by efonidipine. Furthermore, the glomerular area and capillary tuft area were markedly increased in rats treated with efonidipine compared with both control rats (+30 and +42%, respectively, p<0.01) and rats treated with L-NAME (+35 and +56%, respectively, p<0.01)-treated rats. This calcium antagonist also significantly inhibited the both increases of the glomerular cell apoptosis index (-72%) and the PCNA index (+44%), therefore the alteration between apoptosis and proliferation slightly increased the number of glomerular cells (subcapsular, +22%, p<0.01; juxtamedullary, +2%, not significant). Thus, the calcium antagonist efonidipine seems to play an important role in the regulation of apoptosis and proliferation of glomerular cells and may be effective in preventing nephrosclerosis exacerbated by NOS inhibition.     

Role of Nitric Oxide and Endothelin-1 in a Portal Hypertensive Rat Model

Background: Portal hypertension is often accompanied by a hyperdynamic circulation state. Some reports have suggested that nitric oxide (NO) plays an important role in this hyperdynamic state. On the other hand, although endothelin (ET)-1, a powerful vasoconstrictor, was recently identified, little is known about its role in portal hypertension or about the interaction between NO and ET-1. The aim of this study was therefore to investigate whether or not the inhibitor of NO synthase (NOS) might improve portal hypertension, and also to clarify the relationship between NO and ET-1. Methods: Portal hypertensive (PHT) rats, in which hypertension was induced by a two-step ligation of the portal vein (PVL), were used. The mean arterial pressure (MAP), portal pressure (PP), visceral blood flow volume (BFV), and serum levels of NO and ET-1 were determined in PVL rats treated with two NOS inhibitors with different functions: NG-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine (AG). Control (CTR) rats, treated by a sham operation (SO), were also studied. Results: Two-step PVL treatment induced a significant increase in the serum level of NO3- and ET-1 in the portal vein. L-NAME and AG administration significantly decreased PP at doses of 50 mg/kg in PHT rats after 60 min administration, while no inhibitor effected any modification in the CTR rats. Both NOS inhibitors increased MAP and decreased PP and BFV in the portal vein, gastric mucosa, and spleen, in addition to decreasing the serum levels of NO3- and ET-1 in the PHT rats, while neither blockade modified any parameters in the CTR rats. In PHT rats, L-arginine, a NO substance, reversed the effect of L-NAME, while it did not induce any recovery from the AG effect. Conclusions: In PHT rats, NO seems to contribute to portal hypertension. PVL increases not only the serum level of NO3-, but also that of ET-1 in the portal vein. Both L-NAME and AG reduce PP and BFV of the portal vein, spleen, gastric mucosa, and liver. In addition, the inhibition of NOS diminishes the serum level not only of NO, but also of ET-1. Use of an appropriate NOS inhibitor may therefore positively affect the hyperdynamic state in portal hypertension.     

Role of nitric oxide and endothelin-1 in a portal hypertensive rat model

BACKGROUND: Portal hypertension is often accompanied by a hyperdynamic circulation state. Some reports have suggested that nitric oxide (NO) plays an important role in this hyperdynamic state. On the other hand, although endothelin (ET)-1, a powerful vasoconstrictor, was recently identified, little is known about its role in portal hypertension or about the interaction between NO and ET-1. The aim of this study was therefore to investigate whether or not the inhibitor of NO synthase (NOS) might improve portal hypertension, and also to clarify the relationship between NO and ET-1. METHODS: Portal hypertensive (PHT) rats, in which hypertension was induced by a two-step ligation of the portal vein (PVL), were used. The mean arterial pressure (MAP), portal pressure (PP), visceral blood flow volume (BFV), and serum levels of NO and ET-1 were determined in PVL rats treated with two NOS inhibitors with different functions: N(G)-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine (AG). Control (CTR) rats. treated by a sham operation (SO), were also studied. RESULTS: Two-step PVL treatment induced a significant increase in the serum level of NO3-and ET-1 in the portal vein. L-NAME and AG administration significantly decreased PP at doses of 50 mg/kg in PHT rats after 60 min administration, while no inhibitor effected any modification in the CTBR rats. Both NOS inhibitors increased MAP and decreased PP and BFV in the portal vein, gastric mucosa, and spleen, in addition to decreasing the serum levels of NO3- and ET-1 in the PHT rats, while neither blockade modified any parameters in the CTR rats. In PHT rats, L-arginine, a NO substance, reversed the effect of L-NAME, while it did not induce any recovery from the AG effect. CONCLUSIONS: In PHT rats, NO seems to contribute to portal hypertension. PVL increases not only the serum level of NO3-, but also that of ET-1 in the portal vein. Both L-NAME and AG reduce PP and BFV of the portal vein, spleen, gastric mucosa. and liver. In addition, the inhibition of NOS diminishes the serum level not only of NO, but also of ET-1. Use of an appropriate NOS inhibitor may therefore positively affect the hyperdynamic state in portal hypertension.     

一氧化氮和前列腺素在门静脉高压性胃病大鼠胃粘膜灌注中的作用

目的 探讨一氧化氮（NO）和前列腺素在门静脉高压性胃病（PHG）大鼠胃粘膜灌注中的作用。方法 部分结扎大鼠门静脉主干2周后,采用中性红清除率法测定大鼠胃粘膜血流量（GMBF）,同时观察门静脉压力（PVP）的变化。结果 PHG组大鼠GMBF和PVP显著高于假手术组（t=3.431、3．312,P＜0．01）。低剂量的NO合成酶抑制剂L－硝基－精氨酸甲酯（L－NAME）呈剂量依赖性降低PHG大鼠GMBF,而对假手术组GMBF无明显影响;高剂量的L－NAME（12mg/kg)能非常显著降低PHG和假手术组大鼠GMBF。前列腺素环氧合酶抑制剂消炎痛能明显降低PHG组大鼠GMBF,而对假手术组GMBF无明显影响;预先给消炎痛处理后在假手术组大鼠中,静脉注射低剂量L－NAME（4mg/kg)前后GMBF无明显变化,高剂量L－NAME（12mg/kg)降低大鼠的GMBF与未用消炎痛处理组比无明显变化;预先给消炎痛处理后在PHG组大鼠中,L－NAME剂量（4mg/kg、12mg/kg)依赖性降低大鼠的GMBF与未用消炎痛处理组比无明显改变。结论 NO、前列腺素在调节PHG大鼠的GMBF起重要作用,但两者无协同作用。     

Overexpressed nitric oxide synthase in portal-hypertensive stomach of rat: A key to increased susceptibility to damage?

BACKGROUND & AIMS: Portal hypertension predisposes gastric mucosa to increased injury. The aim of this study was to determine whether overexpression of constitutive nitric oxide synthase (cNOS) is responsible for increased susceptibility of portal-hypertensive (PHT) gastric mucosa to damage. METHODS: In gastric specimens from PHT and sham-operated rats, cNOS messenger RNA expression was determined by Northern blotting and cNOS protein expression by Western blotting, immunohistochemistry, and enzyme activity assay. Extent of ethanol- induced gastric mucosal necrosis, mucosal blood flow, and gastric NOS activity in PHT and sham-operated rats was determined after administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) or saline. RESULTS: cNOS messenger RNA level, cNOS enzyme activity, and fluorescence signals for cNOS were increased significantly in PHT rats compared with controls. Inhibition of overexpressed cNOS by L-NAME (5 mg/kg) significantly reduced ethanol-induced mucosal necrosis and normalized blood flow in PHT gastric mucosa, whereas this dose of L- NAME significantly increased mucosal necrosis in sham-operated rats. CONCLUSIONS: Portal hypertension activates the cNOS gene with overexpression of cNOS protein in endothelia of gastric mucosal vessels. Excessive NO production by overexpressed cNOS may play an important role in the increased susceptibility of PHT gastric mucosa to damage. (Gastroenterology 1997 Jun;112(6):1920-30)     

Chronic inhibition of nitric oxide ameliorates splanchnic hyposensitivity to glypressin in a hemorrhage-transfused rat model of portal hypertension

BACKGROUND: Vasopressin given during hemorrhage is less effective than when given during a stable state in experimental portal hypertension or patients with cirrhosis (the so-called hyposensitivity phenomenon). This study investigated whether chronic inhibition of nitric oxide (NO) synthesis by NG-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor, could potentiate the portal-hypotensive effect of glypressin (a long-acting vasopressin analogue) in portal-hypertensive rats during acute bleeding status. METHODS: Portal hypertension was induced by partial portal vein ligation (PVL). Rats were divided to receive either L-NAME (approximately 25 mg/kg/day in tap water) or placebo (tap water) treatment orally from 2 days prior to until 14 days after the operation. At the end of treatment, L-NAME-and placebo-treated PVL rats were subdivided into without-bleeding and with-bleeding groups to assess the effects of glypressin (0.07 mg/kg) on systemic and portal hemodynamics. In rats with a hypotensive hemorrhage, 4.5 ml of blood was withdrawn and 50% of the withdrawn blood was reinfused before the administration of glypressin. RESULTS: As compared with placebo-treated rats, chronic treatment with L-NAME in PVL rats significantly increased mean arterial pressure (P < 0.001) without modulating portal pressure (P > 0.05). In placebo-treated PVL rats, glypressin resulted in a less decrease in portal pressure in rats with bleeding than in those without bleeding (P < 0.05). For PVL rats with bleeding, the portal-hypotensive effect of glypressin was significantly potentiated after chronic L-NAME treatment (P < 0.05). CONCLUSIONS: Chronic inhibition of NO alleviates the splanchnic hyposensitivity to glypressin observed in bleeding PVL rats, suggesting the pathophysiological role of nitric oxide in mediating this splanchnic hyposensitivity.     

Role of endothelin-1 in congestive gastropathy in portal hypertensive rats

BACKGROUND: The aim of this study was to determine the role of endothelin (ET)-1 in portal hypertensive gastropathy (PHG) under portal hypertension, in order to investigate whether the ET(A/B) receptor inhibitor improves the permeability of gastric mucosal microvessels in PHG. METHODS AND RESULTS: Portal hypertensive rats (PVL) and sham-operated rats (CTR) were prepared and then the concentration of plasma ET-1 was measured and the vasopressor response to ET-1 was compared between the two groups. The plasma ET-1 levels in PVL increased significantly compared with CTR; however, the vasopressor response to ET-1 in PVL decreased more than in CTR. Next, the portal venous pressure was measured in both CTR and PVL pretreated with or without a nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), before the injection of ET-1. The portal venous pressure of PVL after receiving ET-1 and being pretreated with L-NAME significantly increased in comparison to the pressure of PVL treated with ET-1 alone (without L-NAME). Moreover, Evans-Blue was injected into each rat and the absorbancy of the gastric contents was measured. The absorbancy of Evans-Blue in PVL increased significantly compared with CTR; however, the absorbancy in PVL+ ET(A/B) receptor inhibitor (Ro47-0203) decreased significantly more than in PVL. CONCLUSIONS: This study showed that ET-1 is a potent vasoconstrictive substance that also has a transitory vasodilative response through NO induced by ET-1 in portal hypertension. In addition, it was found that the vascular permeability of the gastric mucosa increased in portal hypertension and that Ro47-0203 inhibited the hyper-permeability. Accordingly, ET-1 may, thus, play an important role in the development of PHG through NO induced by ET-1. Ro47-0203 may, therefore, be a useful substance for improving PHG in portal hypertension.     

Increased heat-shock protein 90 expression contributes to impaired adaptive cytoprotection in the gastric mucosa of portal hypertensive rats

Background and Aims:  Portal hypertensive (PHT) gastropathy results in an increased susceptibility to damage. Adaptive cytoprotection against ethanol-induced damage is impaired in the gastric mucosa of rats with portal hypertension. Excessive nitric oxide (NO) production occurs in portal hypertension and is mediated in part via heat-shock protein (Hsp)90 production. The aim of this study was to investigate the relation between adaptive cytoprotection after exposure to ethanol and gastric expression of Hsp90 in PHT rats.
Methods:  Portal hypertension was induced in rats by staged portal vein occlusion. Adaptive cytoprotection to 70% ethanol was evaluated by assessing the injury index of the gastric mucosa with or without pretreatment with 10% ethanol. Expression of Hsp90 mRNA was evaluated by real-time polymerase chain reaction, and expression of Hsp90 protein was evaluated by western blotting. The effect of Hsp90 inhibition in PHT rats was evaluated by administration of geldanamycin.
Results:  Gastric Hsp90 mRNA expression in PHT rats was significantly less than that in sham-operated (SO) controls. However, after 10% ethanol pretreatment, Hsp90 mRNA expression was significantly greater in PHT rats than in SO controls. In PHT rats, gastric Hsp90 protein expression after 10% ethanol pretreatment was significantly greater than that without the pretreatment. However, the pretreatment had no effect on the injury index compared to SO rats. Administration of geldanamycin prior to 10% ethanol pretreatment significantly decreased the injury index in response to 70% ethanol in the PHT rats.
Conclusions:  These results show that 10% ethanol pretreatment markedly increases gastric Hsp90 expression in PHT rats. Excessive production of Hsp90 may contribute impaired adaptive cytoprotection.     

Effect of verapamil on nitric oxide synthase in a portal veinligated rat model： Role of prostaglandin

AIM: To investigate the effects of verapamil on nitric oxide (NO) synthesis in a portal vein-ligated rat model. METHODS: Systemic and splanchnic hemodynamics were measured by radiolabeled microspheres in portal hypertensive rats after acute administration of verapamil (2 mg/kg) on chronic treatment with Nw-nitro-L-arginine (NNA)(80 mg/kg) and/or indomethacin (2 mg/kg) . RESULTS: Verapamil (2 mg/kg) caused a marked fall in both arterial pressure and cardiac output accompanied by an insignificant change in the portal pressure and no change in portal venous inflow. This result suggested that verapamil did not cause a reduction in portal vascular resistance of portal hypertensive rats, which was similar between NW- nitro-L-arginine-treated and indomethacin-treated groups. CONCLUSION: In portal hypertensive rats pretreated with NNA and/or indomethacin, acute verapamil administration can not reduce the portal pressure, suggesting that NO and prostaglandin play an important role in the pathogenesis of splanchnic arterial vasodilation in portal hypertension.     

Effect of terlipressin on in vitro vascular hyporeactivity of portal hypertensive rats

Backgrounds/Aims: Isolated vessels of portal hypertensive rats exhibit decreased responsiveness to vasoconstrictors. The vasopressin analogue terlipressin analogue terlipressin is used in the treatment of portal hypertension since it is known to reduce portal pressure, an effect that is thought to arise from splanchnic vasoconstriction via stimulation of vasoconstrictor V₁ receptors. This study assessed the effect of terlipressin on the in vitro vascular reactivity of portal hypertensive rats to the α-adrenoceptor agonist methoxamine.Methods: Portal hypertension was produced by portal vein ligation. Sham-operated rats served as controls. In isolated perfused mesentric arteries of portal vien ligated and sham-operated rats pressor responses to methoxamine (3 nmol-3 μmol) were determined in the absence and presence of the nitric oxide synthase inhibitor N^g-nitro-L-arginine methyl ester (L-NAME; 100 μM), terlipressin or the selective V₂ receptor agonist desmopressin (each 0.5 μM). In addition, the direct pressor properties of terlipressin (3 pmol-100 nmol) were compared to arginine vasopressin (3 pmol-1 nmol) in vessels of normal rats.Results: Mesenteric vessels of portal vein ligated rats were markedly hyporeactive to methoxamine, even in the presence of L-NAME. Terlipressin alone reduced and in combination with L-NAME abolished the difference in reactivity to methoxamine between the portal vein ligated and sham-operated groups, while desmopressin was ineffective. Arginine vasopressin potently contracted vessels of normal rats with a threshold dose of 10 pmol and was maximally effective at 300 pmol. In contrast, terlipressin failed to produce pressor responses up to 100 nmol.Conclusions: Hyporeactivity of mesenteric vessels of portal vein ligated rats to methoxamine is predominantly independent of nitric oxide. Terlipressin alone ameliorates and in combination with L-NAME abolishes the hyporesponsiveness to methoxamine presumably by inhibiting the nitric oxide-independent mechanism that underlies the reduced responsiveness to methoxamine in portal hypertension. This effect of terlipressin appears to be independent of stimulation of V₂ as well as vasoconstrictor V₁ receptors.     

Effect of long-term sucralfate ingestion on antral and fundic epithelial proliferation in the rat

Sucralfate accelerates the healing of chronic gastric ulcers, but its mechanism is not well understood. We studied the effect of long-term administration of sucralfate on gastric epithelial proliferation in the rat by means of tritiated thymidine autoradiography. Rats were treated perorally with 500 mg/kg sucralfate once a day. After 28 days, rats were injected with tritiated thymidine 1µCi/g body weight and sacrificed 1 hr later. Autoradiographs from antral and fundic mucosae were prepared and a number of proliferative measurements were made. Long-term sucralfate administration produced an increase in tritiated thymidine labeling of epithelial cells and expansion of the proliferative zone in antral mucosa. These results indicate that long-term sucralfate ingestion stimulates gastric antral epithelial proliferation in the rat. In light of the fact that chronic gastric ulcers are usually located in the antral region in humans, this enhanced epithelial proliferation may contribute to the beneficial effect of sucralfate in accelerating the healing of gastric ulcers.     

Vasoactive systems in L-NAME hypertension: the role of inducible nitric oxide synthase

OBJECTIVES: The contribution of the renin-angiotensin system (RAS) and the sympathetic nervous system (SNS) to blood pressure (BP) maintenance was evaluated in rats with N(omega)-nitro-L-arginine methyl ester (L-NAME) hypertension. Furthermore, we studied the extent of nitric oxide (NO) synthesis inhibition and the participation of remaining NO in the counterbalance of pressor systems, with a special reference to inducible nitric oxide synthase (iNOS). METHODS: Wistar rats subjected to chronic L-NAME treatment (40 mg/kg per day for 4 weeks) were used. A consecutive blockade of RAS (captopril) and SNS (pentolinium) was followed by acute L-NAME injection. Dimethylguanidine or aminoguanidine were used to affect NO synthesis by iNOS. RESULTS: L-NAME hypertensive rats had borderline augmentation of depressor response to captopril injection, but their BP fall after pentolinium was considerably enhanced compared with controls. Residual BP (recorded after simultaneous blockade of the RAS and the SNS) was elevated by 20-40% in hypertensive rats. Pronounced inhibition of NO synthase activity (50% reduction in the aorta and myocardium) was detected in L-NAME hypertensive rats in which the BP rise elicited by acute L-NAME injection was considerably attenuated (by 60-80%). In contrast, acute administration of dimethylguanidine [mixed endothelial NO synthase (eNOS)/iNOS inhibitor] to hypertensive rats induced a major BP rise similar to that caused by L-NAME injection in controls. Aminoguanidine (a selective iNOS inhibitor) caused a substantial BP rise in L-NAME hypertensive rats only. CONCLUSION: The contribution of SNS to BP maintenance in L-NAME hypertension is more important than that of RAS. In L-NAME hypertensive rats the iNOS becomes a major source of hemodynamically important NO production, which is still insufficient to compensate prevailing vasoconstriction.     

Chronic Inhibition of Nitric Oxide Ameliorates Splanchnic Hyposensitivity to Glypressin in a Hemorrhage-transfused Rat Model of Portal Hypertension

Background: Vasopressin given during hemorrhage is less effective than when given during a stable state in experimental portal hypertension or patients with cirrhosis (the so-called hyposensitivity phenomenon). This study investigated whether chronic inhibition of nitric oxide (NO) synthesis by N^G-nitro-L-arginine methyl ester (L-NAME), a non-selective NO synthase inhibitor, could potentiate the portal-hypotensive effect of glypressin (a long-acting vasopressin analogue) in portal-hypertensive rats during acute bleeding status. Methods: Portal hypertension was induced by partial portal vein ligation (PVL). Rats were divided to receive either L-NAME (~25 mg/kg/day in tap water) or placebo (tap water) treatment orally from 2 days prior to until 14 days after the operation. At the end of treatment, L-NAME-and placebo-treated PVL rats were subdivided into without-bleeding and with-bleeding groups to assess the effects of glypressin (0.07 mg/kg) on systemic and portal hemodynamics. In rats with a hypotensive hemorrhage, 4.5 ml of blood was withdrawn and 50% of the withdrawn blood was reinfused before the administration of glypressin. Results: As compared with placebo-treated rats, chronic treatment with L-NAME in PVL rats significantly increased mean arterial pressure (P &lt; 0.001) without modulating portal pressure (P &gt; 0.05). In placebo-treated PVL rats, glypressin resulted in a less decrease in portal pressure in rats with bleeding than in those without bleeding (P &lt; 0.05). For PVL rats with bleeding, the portal-hypotensive effect of glypressin was significantly potentiated after chronic L-NAME treatment (P &lt; 0.05). Conclusions: Chronic inhibition of NO alleviates the splanchnic hyposensitivity to glypressin observed in bleeding PVL rats, suggesting the pathophysiological role of nitric oxide in mediating this splanchnic hyposensitivity.     

Gastric functions in portal hypertension

This study investigated the effects of portal hypertension on gastric motor and secretory functions and the role of endothelin in rats. Control; sham-operated; endothelin-A receptor blocker, BQ 485 (1 µg/kg) -treated; portal hypertensive; and portal hypertension +, endothelin-A receptor blocker-treated rats were subjected to tests of gastric secretory, motor, and mucosal function studies as well as gastric wall polymorphonuclear infiltration. Portal hypertension was induced by partial portal vein ligation. Portal hypertension suppressed gastric acid and total fluid secretion and delayed gastric emptying. An increase in mucosal permeability and no alteration in gastric wall myeloperoxydase activity were observed. The effects of portal hypertension on gastric secretory, motor, and mucosal functions were reversed by treatment with endothelin-A receptor blocker, BQ-485. It is concluded that portal hypertension suppresses the gastric motor and secretory functions and endothelin plays an important role in the pathophysiology of gastric alterations associated with portal hypertension.     

Neurally-mediated vasodilatation in normal and portal hypertensive rats: role of nitric oxide and calcitonin gene-related peptide

Background/Aims: Portal hypertension is associated with systemic vasodilatation and vascular hyporeactivity, and is reversed by inhibiting nitric oxide biosynthesis. Nitric oxide and calcitonin gene-related peptide are neurotransmitters of non-adrenergic non-cholinergic nerves. The role of nitric oxide and calcitonin gene-related peptide in nerve-stimulated vasodilatation in portal hypertension is unknown.Methods: We tested (i) if in vitro perfused superior mesenteric arterial vascular beds of portal hypertensive rats (induced by partial portal vein ligation) showed an increased vasodilatation to periarterial nerve stimulation compared to normal controls, and (ii) if this vasodilatation was modulated by nitric oxide and calcitonin gene-related peptide antagonism.Results: Vasodilatatory responses to periarterial nerve stimulation (10 V, 1 ms) with increasing frequencies (Hertz, 2–12) in preconstricted vessels (methoxamine and guanethidine) were significantly smaller in vessel preparations of control (n=8) compared to portal hypertensive (n=7) rats, values with 8 Hertz being 32.3±3.6% and 44.9±3.6%, respectively (p<0.05). This difference was reversed by inhibiting nitric oxide and calcitonin gene-related peptide action with the nitric oxide-biosynthesis inhibitor N^ω-Nitro-L-arginine, values for 8 Hertz being 28.7±4.8% (controls) and 37.8±3.3% (portal hypertensive, ns) or with the calcitonin gene-related peptide antagonist CGRP_8–37, values being 25.2±2.8% (controls) and 27.8±4.2% (portal hypertensive, ns), respectively (n=4–6 per group). Vasodilatation to the β-agonist isoproterenol was not significantly different between groups with and without calcitonin gene-related peptide and nitric oxide antagonism.Conclusion: Portal hypertensive rats display a significantly enhanced vasodilatation to periarterial nerve stimulation, which is reversed by inhibiting the non-adrenergic non-cholinergic neurotransmitters nitric oxide and especially calcitonin gene-related peptide.     

Hemodynamic Effects of Eight-Day Octreotide and Propranolol Administration in Portal Hypertensive Rats

Octreotide and propranolol are both effective portal hypotensive drugs in the control or prevention of variceal bleeding. The present study was undertaken to investigate the hemodynamic effects of octreotide and propranolol, alone or in combination, in portal hypertensive rats. Portal hypertension was induced by partial portal vein ligation. Portal hypertensive rats were allocated into one of the four groups: vehicle group (saline, 0.5 ml/day), octreotide group (100 g/kg/12 hr), propranolol group (30 mg/kg/day), and octreotide (100 g/kg/12 hr) plus propranolol (30 mg/kg/day) group. Propranolol or saline was administered by gavage, octreotide by subcutaneous injection. Drug was given one day before ligation and continued for eight consecutive days. Systemic as well as splanchnic hemodynamic parameters were measured thereafter. The portal venous pressure, portal tributary blood flow, and cardiac index were significantly reduced by octreotide, propranolol, or octreotide plus propranolol in portal hypertensive rats. Portal territory, systemic, and renal vascular resistances were significantly enhanced, while hepatic arterial blood flow significantly reduced, in the octreotide and octreotide plus propranolol groups as compared to vehicle group. Our results showed that eight-day administration of octreotide, propranolol, or octreotide plus propranolol led to portal hypotensive and antihyperdynamic effects in portal hypertensive rats. Overall, octreotide treatment alone resulted in better antihyperdynamic profiles than propranolol treatment alone. The combination of octreotide and propranolol offered no therapeutic benefits and was slightly less effective than octreotide alone.