Portal hypertensive response to kinin.

Portal hypertension is the most common complication of chronic liver diseases, such as cirrhosis. The increased intrahepatic vascular resistance seen in hepatic disease is due to changes in cellular architecture and active contraction of stellate cells. In this article, we review the historical aspects of the kallikrein-kinin system, the role of bradykinin in the development of disease, and our main findings regarding the role of this nonapeptide in normal and experimental models of hepatic injury using the isolated rat liver perfusion model (mono and bivascular) and isolated liver cells. We demonstrated that: 1) the increase in intrahepatic vascular resistance induced by bradykinin is mediated by B2 receptors, involving sinusoidal endothelial and stellate cells, and is preserved in the presence of inflammation, fibrosis, and cirrhosis; 2) the hepatic arterial hypertensive response to bradykinin is calcium-independent and mediated by eicosanoids; 3) bradykinin does not have vasodilating effect on the pre-constricted perfused rat liver; and, 4) after exertion of its hypertensive effect, bradykinin is degraded by angiotensin converting enzyme. In conclusion, the hypertensive response to BK is mediated by the B2 receptor in normal and pathological situations. The B1 receptor is expressed more strongly in regenerating and cirrhotic livers, and its role is currently under investigation.

Portal hypertensive response to kinin

Portal hypertension is the most common complication of chronic liver diseases, such as cirrhosis. The increased intrahepatic vascular resistance seen in hepatic disease is due to changes in cellular architecture and active contraction of stellate cells. In this article, we review the historical aspects of the kallikrein-kinin system, the role of bradykinin in the development of disease, and our main findings regarding the role of this nonapeptide in normal and experimentalmodels of hepatic injury using the isolated rat liver perfusion model (mono and bivascular) and isolated liver cells. We demonstrated that: 1) the increase in intrahepatic vascular resistance induced by bradykinin is mediated by B2 receptors, involving sinusoidal endothelial and stellate cells, and is preserved in the presence of inflammation, fibrosis, and cirrhosis; 2) the hepatic arterial hypertensive response to bradykinin is calcium-independent and mediated by eicosanoids; 3) bradykinin does not have vasodilating effect on the pre-constricted perfused rat liver; and, 4) after exertion of its hypertensive effect, bradykinin is degraded by angiotensin converting enzyme. In conclusion, the hypertensive response to BK is mediated by the B2 receptor in normal and pathological situations. The B1 receptor is expressed more strongly in regenerating and cirrhotic livers, and its role is currently under investigation.

Hipertensão portal é a complicação mais comum das doenças crônicas do fígado, tais como cirrose. A resistência intravascular aumentada observada na doença hepática é devida a alterações na arquitetura celular e contração ativa das células estreladas. Neste trabalho revisamos aspectos históricos do estudo do sistema calicreína-cinina e os resultados de nossos estudos do papel deste nonapeptídeo no controle do tono vascular intra-hepático em condições normais e modelos experimentais de agressão hepática usando a perfusão de fígado isolado de rato (mono e bivascular) e células hepáticas isoladas. Nós demonstramos que: 1) o aumento da resistência vascular intrahepática induzido pela bradicinina é mediado por receptores B2, envolve a participação de células endoteliais sinusoidais e células estreladas e não é alterada pela presença de inflamação, fibrose ou cirrose; 2) a resposta hipertensiva induzida pela bradicinina no sistema arterial hepático é cálcio-independente emediada por eicosanóides; 3) bradicinina não tem efeito dilatador na circulação intra-hepática; 4) após exercer efeito vasoconstritor intra-hepático, a bradicinina é degradada pela enzima conversora de angiotensina. Em conclusão, a resposta hipertensiva à bradicinina é mediada pelo receptor B2 em condições normais e patológicas. Receptor B1 é expresso mais fortemente nos fígados em regeneração e cirróticos e seu papel está sob investigação.

Nitric oxide and vascular remodeling modulate hepatic arterial vascular resistance in the isolated perfused cirrhotic rat liver.

BACKGROUND/AIMS: Hepatic arterial resistance is modulated by the hepatic arterioles but the role of NO and vascular remodeling in hepatic arterial resistance in cirrhosis is unknown. METHODS: Cirrhosis was induced by CCl(4) or BDL. Using a bivascular liver perfusion dose-responses curves to methoxamine were obtained from the hepatic artery in absence and presence of L-NMMA. Lumen-diameter, wall thickness and number of smooth muscle nuclei were quantitated in the arteries using image analysis. RESULTS: Hepatic arterial resistance and the response to methoxamine were lower in cirrhosis compared to controls (p< or = 0.04) and lower in BDL compared to CCl(4) (p< or = 0.01). L-NMMA increased the response to methoxamine in CCl(4) (p=0.002) and BDL (p=0.05) but corrected the response only in CCl(4) (p=n.s. vs. control). Wall thickness and the number of smooth muscle nuclei were significantly smaller in cirrhosis compared to controls (p<0.05) and the number of nuclei was also lower in BDL compared to CCl(4) (p=0.005). CONCLUSIONS: NO is the main modulator of hepatic arterial resistance in CCl(4) but not in BDL. Intrahepatic arterial remodeling is present in both cirrhotic models but is greater in BDL. This indicates a larger role of structural changes in the control of hepatic arterial resistance in BDL.

The role of hepatic arterial flow on portal venous and hepatic venous wedged pressure in the isolated perfused CCl4-cirrhotic liver.

In cirrhosis, hepatic venous pressure gradient is used to measure portal venous and sinusoidal pressures, as well as drug-induced decreases of elevated pressures. The aim of this study was to investigate the influence of hepatic arterial flow (HAF) changes on portal venous perfusion (PVPP) and wedged hepatic venous pressure (WHVP). Normal and CCl4-cirrhotic rats were subjected to a bivascular liver perfusion with continuous measurements of PVPP, WHVP, and hepatic arterial perfusion pressure. Flow-pressure curves were performed with the use of different flows either through the portal vein (PVF: 20-32 ml/min) or HAF (5-15 ml/min). Increases in HAF lead to significant absolute and relative increases in PVPP (P = 0.002) and WHVP (P < 0.001). Absolute changes in HAF correlated to absolute changes in PVPP (cirrhosis: r = 0.64, P < 0.001; control: r = 0.67, P < 0.001) and WHVP (cirrhosis: r = 0.71, P < 0.001; control: r = 0.82, P < 0.001). Changes in PVPP correlated to changes in WHVP due to changes in PVF only in cirrhosis (r = 0.75, P < 0.001), whereas changes in HAF correlated in both cirrhosis (r = 0.92, P < 0.001) and control (r = 0.77, P < 0.001). In conclusion, increases and decreases in HAF lead to respective changes in PVPP and WHVP. This suggests a direct influence of HAF on PVPP and WHVP most likely due to changes in sinusoidal perfusion.

Decreased intrahepatic response to alpha(1)-adrenergic agonists in lipopolysaccharide-treated rats is located in the sinusoidal area and depends on Kupffer cell function.

BACKGROUND AND AIM: Livers from lipopolysaccharide-treated rats have a decreased vascular response to alpha(1)-adrenergic agonists due to an increased production of nitric oxide. Kupffer cells play a central role in the development of intrahepatic microvascular abnormalities during endotoxemia. We investigated the role of Kupffer cells in the intrahepatic vascular tone control in normal and endotoxemic rats. METHOD: Twenty-four hours after pretreatment with gadolinium chloride (to eliminate/inactivate Kupffer cells) or saline, rats were treated with lipopolysaccharide or a second dose of saline. Six hours later, rats (under deep anesthesia) were submitted to liver perfusion with Krebs-Henseleit solution using a system that allowed the measurement of both perfusion and sinusoidal pressures. Dose-response curves to methoxamine (alpha(1)-adrenergic agonist) were obtained in the absence or the presence of the nitric oxide synthase inhibitor N-monomethyl-L-arginine. RESULTS: Pretreatment with gadolinium did not change the intrahepatic vascular response to methoxamine in normal livers. Livers from lipopolysaccharide-treated rats showed a decreased sinusoidal vascular response to methoxamine and a 10-fold increase in nitric oxide production during liver perfusion. Either pretreatment with gadolinium or the presence of N-monomethyl-L-arginine in the perfusate restored the response to methoxamine and decreased the nitric oxide overproduction by more than 50%. CONCLUSIONS: Kupffer cells neither mediate nor modulate the intrahepatic vascular response to alpha(1)-adrenergic agonists in normal livers. Reduction in intrahepatic vascular response to alpha(1)-adrenergic agonists in livers from lipopolysaccharide-treated rats is located in the sinusoidal area and depends on Kupffer cell function.

Increased phosphodiesterase-5 expression is involved in the decreased vasodilator response to nitric oxide in cirrhotic rat livers.

BACKGROUND/AIMS: Cirrhotic livers have a deficient vasodilator response to nitric oxide (NO). The vasodilator effect of NO is normally limited by the degradation of its second messenger cyclic guanosine 3', 5' monophosphate by phosphodiesterases. We investigated (1) the phosphodiesterase-5 (PDE-5) expression in normal and cirrhotic rat livers, (2) the location of the deficient response to NO in cirrhotic livers, and (3) the effect of the PDE-5 inhibitor Sildenafil citrate on this deficient response. METHODS: Normal and ascitic cirrhotic rats were subjected to liver perfusion with continuous measurement of both perfusion and sinusoidal (wedge hepatic) pressures. After incubation with N-monomethyl-l-arginine and pre-constriction with Methoxamine, concentration-response curves to the spontaneous NO donor S-nitroso-N-acetylpenicillamine were obtained in the absence or presence of Sildenafil (10(-8)M). RESULTS: PDE-5 expression (Western blot) in cirrhotic livers was higher than in normal livers (P=0.042). Compared to normal livers, cirrhotic livers showed a decreased response to S-nitroso-N-acetylpenicillamine in the pre-sinusoidal area (P=0.003) but not in the sinusoidal/post-sinusoidal area (P=0.433). In the presence of Sildenafil, normal and cirrhotic livers showed similar pre-sinusoidal (P=0.419) and sinusoidal/post-sinusoidal (P=0.875) responses to S-nitroso-N-acetylpenicillamine. CONCLUSIONS: Increased PDE-5 expression is involved in the decreased vascular response to NO in cirrhotic livers.

A liver-specific nitric oxide donor improves the intra-hepatic vascular response to both portal blood flow increase and methoxamine in cirrhotic rats.

BACKGROUND/AIMS: A decreased intra-hepatic nitric oxide (NO) production participates on the pathogenesis of portal hypertension in cirrhosis. We tested the hemodynamic effects of a liver-specific NO donor (NCX-1000) derived from ursodeoxycholic acid in portal hypertensive cirrhotic rats. METHODS: After a 14-day treatment with ursodeoxycholic acid or NCX-1000 by gavage, ascitic cirrhotic rats (CCl4-induced) were used in two studies: (1) in vivo mean arterial pressure (MAP), portal pressure (PP) and superior mesenteric artery (SMA) blood flow measurements before and during progressive blood volume expansion (blood infusion); and (2) in situ liver perfusion to obtain dose/response curves to methoxamine (alpha1-adrenergic agonist) and flow/pressure curves. RESULTS: Basal heart rate, MAP, and PP were similar in both groups. During blood infusion, similar MAP and SMA flow increases were observed in both groups; however, PP increase observed in control rats was blunted in NCX-1000 treated rats (P=0.015). In liver perfusions, flow/pressure curves were similar in both groups; however, NCX-1000-treated livers showed a lower response to methoxamine (P=0.016). cGMP concentration in NCX-1000-treated livers was higher (P=0.015) than in controls. CONCLUSIONS: Treatment with a liver-specific NO donor improves the portal system adaptability to portal blood flow increase and ameliorates the intra-hepatic response to methoxamine in cirrhotic rats.

Deficit in nitric oxide production in cirrhotic rat livers is located in the sinusoidal and postsinusoidal areas.

Intrahepatic nitric oxide (NO) production is decreased in cirrhotic livers. Our objective was to identify, in cirrhotic rat livers, intrahepatic vascular segments where the deficit of NO facilitates the effect of vasoconstrictors. By using a modified rat liver perfusion system with measurement of both the perfusion and sinusoidal (wedged hepatic vein) pressures, we studied the effect of the NO synthase blocker N(omega)-nitro-l-arginine (l-NNA) on the response to methoxamine (alpha(1)-adrenoreceptor agonist) in different segments of the intrahepatic circulation of normal and cirrhotic rat livers. l-NNA enhanced the presinusoidal, sinusoidal, and postsinusoidal responses to methoxamine in normal livers as well as the presinusoidal response in cirrhotic livers. However, l-NNA did not change the already enhanced sinusoidal/postsinusoidal response to methoxamine in cirrhotic livers. The postsinusoidal response to methoxamine was higher in cirrhotic rats with ascites than in those without ascites. We concluded that NO modulates the presinusoidal, sinusoidal, and postsinusoidal vascular tone in normal livers. NO production in cirrhotic rat livers is severely impaired in the sinusoidal and postsinusoidal areas but is preserved in the presinusoidal area, as evidenced by its normal response to l-NNA. We speculate that an increased postsinusoidal response to catecholamines may participate in the genesis of ascites in cirrhosis.

Bioactivation of nitroglycerin and vasomotor response to nitric oxide are impaired in cirrhotic rat livers.

Nitroglycerin (NTG), a nitric oxide (NO) donor, has been shown to reduce portal pressure in cirrhotic patients. Using the in situ perfusion of normal and cirrhotic rat livers, we compared the vascular relaxation induced by either NTG or the spontaneous nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP). Normal and cirrhotic livers were perfused (40 mL/min, 37 degrees C) with Krebs' solution in a recirculating system. After preconstriction with methoxamine (10(-4) mol/L), a dose-response study was performed using 6 cumulative doses of NTG or SNAP (10(-7) to 3 x 10(-5) mol/L). NO(x) (NO(-)(2) + NO(-)(2) production in the perfusate was measured by chemiluminescence. Cirrhotic livers exhibited lower vasorelaxant responses, compared with normal livers, to both NTG (P <.0001) and SNAP (P =.0020). In normal livers, NTG and SNAP induced similar vasorelaxant responses (P =.44). In cirrhotic livers, NTG induced less vasorelaxation than SNAP (P <.0001). In the presence of NTG (P =.0045), but not SNAP (P =.99), NO(x) production in experiments with cirrhotic livers was lower than in experiments with normal livers. In conclusion, in cirrhotic rat livers, the vasorelaxant response to NTG is impaired owing to both a decreased metabolism of this NO donor and an inability of the hepatic vasculature to respond to NO.