Portal Hypertensive Animals Research Articles

Brain network function during shifts in learning strategies in portal hypertension animals.

Patients with minimal hepatic encephalopathy exhibit early impairments in their ability to shift attentional set. We employed a task-switching protocol to evaluate brain network changes. Strategy switching requires the modification of both the relevant stimulus dimension and the required memory system. Rats were trained in an allocentric (A) and a cue-guided (C) task using a four-arm maze. To examine priming, we changed the order in which the tasks were presented. Five groups of animals were used: a SHAM (sham-operated) A-C group (n=10), a SHAM C-A group (n=8), a PH (portal hypertension) A-C group (n=8), PH C-A group (n=8), and a naïve group (n=10). The triple portal vein ligation method was used to create an animal model of the early evolutive phase of PH. The animals were tested in the four-arm radial water maze in a single 10-trial session each day for six days (three days for the allocentric task and three days for the cue-guided task). The metabolic activities of the brains were studied with cytochrome oxidase histochemistry, and brain network changes were assessed with principal component analysis. The behavioural results revealed significant increases in the numbers of correct choices across training days in all groups studied, and facilitation of the acquisition of the second task was present in the C-A groups. Moreover, different brain network activities were found; in the experimental groups, the performance of A-C switch involved the prefrontal cortex, and the key structures involved in the C-A switch in the other groups were the dentate gyrus of the dorsal hippocampus and the basolateral and central amygdala. These networks have a common nucleus of structures (i.e., the parietal cortex and the dorsal and ventral striatum), whereas other structures were specifically involved in each type of strategy, suggesting that these regions are part of both circuits and may interact with one another during learning.

Morphological and Biomechanical Remodeling of the Hepatic Portal Vein in a Swine Model of Portal Hypertension

To obtain the morphological and biomechanical remodeling of portal veins in swine with portal hypertension (PHT), so as to provide some mechanical references and theoretical basis for clinical practice about PHT. Twenty white pigs were used in this study, 14 of them were subjected to both carbon tetrachloride- and pentobarbital-containing diet to induce experimental liver cirrhosis and PHT, and the remaining animals served as the normal controls. The morphological remodeling of portal veins was observed. Endothelial nitric oxide synthase expression profile in the vessel wall was assessed at both mRNA and protein level. The biomechanical changes of the hepatic portal veins were evaluated through assessing the following indicators: the incremental elastic modulus, pressure-strain elastic modulus, volume elastic modulus, and the incremental compliance. The swine PHT model was successfully established. The percentages for the microstructural components and the histological data significantly changed in the experimental group. Endothelial nitric oxide synthase expression was significantly downregulated in the portal veins of the experimental group. Three incremental elastic moduli (the incremental elastic modulus, pressure-strain elastic modulus, and volume elastic modulus) of the portal veins from PHT animals were significantly larger than those of the controls (P < 0.05), whereas the incremental compliance of hepatic portal vein decreased. Our study suggests that the morphological and biomechanical properties of swine hepatic portal veins change significantly during the PHT process, which may play a critical role in the development of PHT and serve as potential therapeutic targets during clinical practice.

Vascular corrosion casting: analyzing wall shear stress in the portal vein and vascular abnormalities in portal hypertensive and cirrhotic rodents

Vascular corrosion casting is an established method of anatomical preparation that has recently been revived and has proven to be an excellent tool for detailed three-dimensional (3D) morphological examination of normal and pathological microcirculation. In addition, the geometry provided by vascular casts can be further used to calculate wall shear stress (WSS) in a vascular bed using computational techniques. In the first part of this study, the microvascular morphological changes associated with portal hypertension (PHT) and cirrhosis in vascular casts are described. The second part of this study consists of a quantitative analysis of the WSS in the portal vein in casts of different animal models of PHT and cirrhosis using computational fluid dynamics (CFD). Microvascular changes in the splanchnic, hepatic and pulmonary territory of portal hypertensive and cirrhotic mice are described in detail with stereomicroscopic examination and scanning electron microscopy. To our knowledge, our results are the first to report the vascular changes in the common bile duct ligation cirrhotic model. Calculating WSS using CFD methods is a feasible technique in PHT and cirrhosis, enabling the differentiation between different animal models. First, a dimensional analysis was performed, followed by a CFD calculation describing the spatial and temporal WSS distributions in the portal vein. WSS was significantly different between sham/cirrhotic/pure PHT animals with the highest values in the latter. Up till now, no techniques have been developed to quantify WSS in the portal vein in laboratory animals. This study showed for the first time that vascular casting has an important role not only in the morphological evaluation of animal models of PHT and cirrhosis, but also in defining the biological response of the portal vein wall to hemodynamic changes. CFD in 3D geometries can be used to describe the spatial and temporal variations in WSS in the portal vein and to better understand the forces affecting mechanotransduction in the endothelium.

Sepsis Worsening Vascular Hyporeactivity of the Superior Mesenteric Artery in Portal Vein-ligated Rats

Vascular hyporeactivity is observed in portal hypertensive animals and septic rats. The objective of this study was to investigate whether impairment of superior mesenteric artery vascular contractility in the portal hypertensive rat was further impaired after sepsis. Sepsis was induced by cecum ligation and puncture (CLP) in male portal hypertensive Sprague-Dawley rats that had been subjected to portal vein ligation (PVL) for 14 days. Hemodynamic studies, isolated vascular ring studies, microbiological studies, and plasma nitrite/nitrate measurements were performed 2, 6, and 18 hours after CLP. An additional group of PVL rats received prophylactic imipenem (10 mg intravenously for 1 hour) before CLP and then were studied 6 hours after CLP. Mean arterial pressure and heart rate of PVL rats were significantly decreased shortly after CLP. CLP caused further nitric oxide production and vascular hyporesponsiveness 6 and 18 hours after CLP compared with the baseline portal hypertensive group. Vascular hyporeactivity was corrected by N-nitro-L-arginine methyl ester + 1400W (1400W is N-(3-(aminomethyl)benzyl)acetamidine hydrochloride, a selective inducible nitric oxide synthase inhibitor). Prophylactic imipenem did not alter nitric oxide production or vascular contractility after sepsis induced by CLP. Our study showed that vascular contractility in portal hypertensive rats is further impaired soon after CLP-induced sepsis.

Rapamycin prevents mesenteric neo‐angiogenesis and reduces splanchnic blood flow in portal hypertensive mice

Increased angiogenesis in the mesenteric microvasculature of portal hypertensive animals may contribute to the development of splanchnic vasodilation associated with portal hypertension (PHT). Experimental data suggest that rapamycin may reduce angiogenesis and tumour growth by inhibiting the vascular endothelial growth factor (VEGF) pathway. This study determines whether rapamycin can prevent the neoangiogenesis in the mesentery of portal hypertensive mice and may influence the splanchnic vasodilation. PHT was induced by partial portal vein ligation (PPVL). PPVL and Sham mice were treated daily with rapamycin or placebo for 2 weeks. Protein expressions of VEGF, CD 31, Akt and p70S6 kinase (mTOR signalling pathway) were evaluated. Mesenteric blood flow (MBF) was measured by a perivascular flow probe. Increased mesenteric angiogenesis and VEGF protein levels were observed in PPVL(placebo) mice compared to Sham(placebo) mice. Rapamycin treatment caused significant reduction in CD 31 positive endothelial cells and VEGF protein in the PPVL(rapamycine) group compared to the PPVL(placebo) group, to levels comparable with Sham(placebo) and Sham(rapamycine) groups. MBF was significantly higher in PPVL(placebo) mice compared to the Sham(placebo) mice. Rapamycin decreased significantly the MBF in PPVL(rapamycine) mice compared to PPVL(placebo) mice. Phospo-Akt and p70S6 kinase protein levels were increased in the mesenteric tissue of PPVL(placebo) mice compared to Sham(placebo) mice, which were also prevented by treatment with rapamycin. An increased VEGF dependent neo-angiogenesis is present in the mesentery of portal hypertensive mice. Rapamycin prevents angiogenesis in the mesenteric tissue and decreases the mesenteric blood flow in portal hypertensive mice, at least in part through an anti-VEGF activity and influence on the mTOR signalling pathway.

Modulation of pulmonary endothelial endothelin B receptor expression and signaling: implications for experimental hepatopulmonary syndrome

The hepatopulmonary syndrome (HPS) results from intrapulmonary vasodilation in the setting of cirrhosis and portal hypertension. In experimental HPS, pulmonary endothelial endothelin B (ET(B)) receptor overexpression and increased circulating endothelin-1 (ET-1) contribute to vasodilation through enhanced endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) production. In both experimental cirrhosis and prehepatic portal hypertension, ET(B) receptor overexpression correlates with increased vascular shear stress, a known modulator of ET(B) receptor expression. We investigated the mechanisms of pulmonary endothelial ET(B) receptor-mediated eNOS activation by ET-1 in vitro and in vivo. The effect of shear stress on ET(B) receptor expression was assessed in rat pulmonary microvascular endothelial cells (RPMVECs). The consequences of ET(B) receptor overexpression on ET-1-dependent ET(B) receptor-mediated eNOS activation were evaluated in RPMVECs and in prehepatic portal hypertensive animals exposed to exogenous ET-1. Laminar shear stress increased ET(B) receptor expression in RPMVECs without altering mRNA stability. Both shear-mediated and targeted overexpression of the ET(B) receptor enhanced ET-1-mediated ET(B) receptor-dependent eNOS activation in RPMVECs through Ca(2+)-mediated signaling pathways and independent of Akt activation. In prehepatic portal hypertensive animals relative to control, ET-1 administration also activated eNOS independent of Akt activation and triggered HPS. These findings support that increased pulmonary microvascular endothelial ET(B) receptor expression modulates ET-1-mediated eNOS activation, independent of Akt, and contributes to the development of HPS.

Impaired agonist-dependent myosin phosphorylation and decreased RhoA in rat portal hypertensive mesenteric vasculature

The purpose of the present study was to examine the effects of portal hypertension on agonist-induced myosin phosphorylation and RhoA expression in vascular smooth muscle. A possible link to cAMP-dependent events was also examined. Portal hypertension was produced by stenosis of the portal vein. Vessel segments were treated with or without 50 microM of the PKA inhibitor Rp-cAMPS for 30 min and subsequently stimulated with 10(-4) M phenylephrine. Myosin regulatory light-chain phosphorylation was detected by immunoblotting. Total RNA from first-order mesenteric arteries and portal veins was isolated and amplified by RT-PCR using RhoA and GAPDH primers. RhoA protein expression was also measured in first-order mesenteric arteries using Western blot analysis. Myosin phosphorylation in maximally stimulated first-order mesenteric arteries was significantly lower in portal hypertensive animals (19.9 +/- 2.86%) when compared with sham-operated control (43.8 +/- 3.53%). Inhibition of PKA selectively increased myosin phosphorylation to 34.7 +/- 4.18%. Rp-cAMPS did not affect the phosphorylation of the portal veins or superior mesenteric arteries. RhoA mRNA and membrane-associated RhoA protein expression in portal hypertensive first-order mesenteric arteries were significantly lower when compared with controls. Acute inhibition of PKA had no effect on RhoA mRNA expression. However, it restored membrane-associated RhoA protein expression in portal hypertensive vessels to control levels. The results suggest that reductions in membrane-associated RhoA expression, which appear to be regulated by cAMP-dependent events, lead to reduced myosin phosphorylation and may underlie the reduced vasoconstrictor effectiveness in the resistance vasculature of portal hypertensive intestine.

Deletion of inducible nitric oxide synthase decreases mesenteric vascular responsiveness in portal hypertensive mice

The effects of pre-hepatic portal hypertension were examined on the responsiveness of aorta and mesenteric artery from wild-type, inducible nitric oxide synthase knockout (iNOS-KO) and endothelial nitric oxide synthase knockout (eNOS-KO) mice. Mice were sham-operated or made portal hypertensive by creating a calibrated portal vein stenosis. Acetylcholine produced marked relaxations in phenylephrine (10 μM) contracted aorta and mesenteric artery from wild-type and iNOS-KO, both sham and portal hypertensive, but relaxations were abolished in vessels from eNOS-KO mice. There were no significant differences between sham and portal hypertensive animals within groups in the effects of acetylcholine. The potency of KCl was significantly increased in aorta and mesenteric artery from eNOS-KO mice. The maximum contraction to the α 1-adrenoceptor agonist phenylephrine was significantly increased in aorta from eNOS-KO, as compared with wild-type mice. There were no significant differences between sham and portal hypertensive animals within each group in contractions of aorta to KCl or phenylephrine. However, in mesenteric artery, although portal hypertension did not change responsiveness in wild-type or eNOS-KO as compared to sham animals, the potency of phenylephrine was significantly reduced in portal hypertensive iNOS-KO mice as compared to shams. Hence, portal hypertension as compared to sham operation did not affect responses to vasoconstrictors in mouse aorta, but in mouse mesenteric artery portal hypertension affected vascular responses in iNOS-KO mice, suggesting that iNOS is involved in the mesenteric vascular response to portal vein ligation.

Increased pulmonary vascular endothelin B receptor expression and responsiveness to endothelin-1 in cirrhotic and portal hypertensive rats: a potential mechanism in experimental hepatopulmonary syndrome

Background/Aims: In experimental hepatopulmonary syndrome (HPS), hepatic endothelin-1 (ET-1) release during common bile duct ligation (CBDL) and ET-1 infusion in pre-hepatic portal hypertension after portal vein ligation (PVL) initiate vasodilatation through an endothelin B receptor mediated increase in pulmonary endothelial nitric oxide synthase (eNOS). We evaluated if pulmonary ET receptor expression changes in experimental cirrhosis and portal hypertension and confers susceptibility to HPS. Methods: In normal, PVL and CBDL animals, lung ET receptor expression and localization were assessed and ET receptor levels and functional analysis of ET-1 effects on eNOS levels were evaluated in intralobar pulmonary artery (PA) and aortic (AO) segments. Normal rats underwent evaluation for HPS after ET-1 infusion. Results: There was a selective increase in ET B receptor expression in the pulmonary vasculature from PVL and CBDL animals. ET-1 stimulated NO production and an ET B receptor mediated increase in eNOS levels in PA segments from PVL and CBDL animals, but not normal animals. ET-1 did not alter lung eNOS levels or cause HPS in normal rats. Conclusions: ET B receptor expression and ET-1 mediated eNOS and NO production are enhanced in the lung vasculature in cirrhotic and portal hypertensive animals and correlate with in vivo susceptibility to ET-1 mediated HPS.

Mice with targeted deletion of eNOS develop hyperdynamic circulation associated with portal hypertension.

Systemic vasodilation is the initiating event of the hyperdynamic circulatory state, being most likely triggered by increased levels of vasodilators, primarily nitric oxide (NO). Endothelial NO synthase (eNOS) is responsible for this event. We tested the hypothesis that gene deletion of eNOS and inducible NOS (iNOS) may inhibit the development of the hyperdynamic circulatory state in portal hypertensive animals. To test this hypothesis, we used mice lacking eNOS (eNOS-/-) or eNOS/iNOS (eNOS/iNOS-/-) genes. A partial portal vein ligation (PVL) was used to induce portal hypertension. Sham-operated animals were used as a control. Hemodynamic characteristics were tested 2 wk after surgery. As opposed to our hypothesis, PVL also caused significant reduction in peripheral resistance in eNOS-/- compared with sham animals (0.33 +/- 0.02 vs. 0.41 +/- 0.03 mmHg. min x kg body wt x ml(-1); P = 0.04) and in eNOS/iNOS-/- animals with PVL compared with that of the sham-operated group (0.44 +/- 0.02 vs. 0.54 +/- 0.04; P = 0.03). This demonstrates that, despite gene deletion of eNOS, the knockout mice developed hyperdynamic circulation. Compensatory vasodilator molecule(s) are upregulated in place of NO in the systemic and splanchnic circulation in portal hypertensive animals.

Adenosine A(2A) receptors in portal hypertension: their role in the abnormal response to adenosine of the cranial mesenteric artery in rabbits.

1. Adenosine is a regulator of mesenteric vasodilation involved in auto-regulation and post-prandial hyperemia, but the adenosine receptor subtype involved in this relaxant effect is poorly characterized. We have now pharmacologically characterized this receptor in rabbit mesenteric arteries and investigated how this adenosine receptor response changes in portal hypertensive animals since the adenosine response is decreased. 2. The closest non-metabolisable adenosine analogue, 2-chloroadenosine (CADO), the mixed A(1)/A(2) receptor agonist, 5'-ethylcarboxamidoadenosine (NECA), and the selective A(2A) receptor agonist, 2-[4-(2-p-carbonyethyl)phenylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680) (1 pM -- 1 mM) relaxed noradrenaline pre-contracted arteries with a rank order of potency of CGS 21680 (EC(50)=20 nM) > or = NECA (60 nM)>>CADO (640 nM). 3. The selective A(2A) receptor antagonist, 4-(2-[7-amino-2-(2-furyl)-[1,2,4]-triazolo[2,3-a][1,3,5]-triazin-5-ylamino]ethyl)phenol (ZM 241385, 100 nM), shifted to the right the CADO concentration-response curve. 4. In portal hypertensive animals, there was mainly a decreased potency but also a decreased efficacy of all tested adenosine agonists compared to normal animals. Concomitantly, there was a decreased adenosine plasma level and a decreased binding density of [(3)H]-CGS 21680 and [(3)H]-ZM 241385 to mesenteric artery membranes from portal hypertensive compared to normal rabbits. 5. These results indicate that A(2A) receptor activation is required for the adenosine-induced mesenteric relaxation and that the decreased density of A(2A) receptors may contribute to the decreased relaxation induced by adenosine of mesenteric arteries in portal hypertensive animals.

Hemodynamic Effects of a Combination of Octreotide and Terlipressin Patients with Viral Hepatitis Related Cirrhosis

Background: Terlipressin or octreotide given alone has been used as the first-line pharmacological treatment for acute variceal bleeding. In portal hypertensive animals, pre-infusion of octreotide followed by the addition of terlipressin has an additive or complementary effect on splanchnic hemodynamics. The current study was aimed at evaluating such a combination treatment in patients with cirrhosis and portal hypertension. Methods: Patients were randomly assigned to receive either a placebo ( n = 11) or an intravenous infusion of octreotide 100 μg/h after an initial bolus of 100 μg ( n = 13). Thereafter, each patient received an intravenous injection of terlipressin 2 mg. Hemodynamic values were measured basally, 30 min after octreotide or placebo, and 60 min after terlipressin. Results: Placebo administration did not affect any of the hemodynamic values. Terlipressin administration resulted in expected changes in hepatic venous pressure gradient, hepatic blood flow and systemic hemodynamics. In contrast, octreotide administration significantly decreased hepatic blood flow but did not affect other hemodynamic values. After terlipressin administration, significant hemodynamic changes were observed that were similar to the hemodynamic changes with terlipressin alone. The magnitude of changes in hepatic venous pressure gradient, cardiac index and systemic vascular resistance were no different between the two groups of patients. The heart rate was significantly lower in patients receiving octreotide plus terlipressin than those receiving terlipressin alone. Conclusion: The current study showed that a combination of octreotide and terlipressin did not exert an additive effect in reducing hepatic venous pressure gradient in patients with cirrhosis. In addition, the systemic hemodynamic changes were comparable between the two groups.

Hemodynamic, Metabolic and Hormonal Responses to Oral Glibenclamide in Patients with Cirrhosis Receiving Glucose

Background: In patients with cirrhosis, glucose may induce splanchnic and renal vasodilation. Since the antidiabetic sulfonylurea glibenclamide is known to induce splanchnic and renal vasoconstriction in portal hypertensive animals, this drug may inhibit glucose-induced hemodynamic responses in patients with cirrhosis. The aim of the present study was to investigate, in patients with cirrhosis, the short-term effects of glibenclamide on hemodynamic and humoral responses to glucose. Methods: Patients were randomly assigned to receive either glibenclamide (5-mg tablet) or a placebo. All patients received an infusion of 10% glucose (62.5 ml/h for 12 h) that was started at the same time as glibenclamide or placebo administration. Studies were performed prior to and 90 min after glibenclamide or placebo. Results: Glibenclamide (i.e. glibenclamide plus glucose) significantly increased plasma insulin concentrations and glycemia while placebo (i.e. glucose alone) significantly increased glycemia but did not change plasma insulin levels. Glibenclamide did not significantly change the hepatic venous pressure gradient while this value was significantly increased following glucose alone. Glibenclamide did not significantly change renal blood flow and glomerular filtration rate while glucose alone significantly increased renal blood flow without affecting the glomerular filtration rate. Glibenclamide significantly decreased cardiac index while glucose alone did not change this value. Conclusions: In patients with cirrhosis receiving glucose, glibenclamide blunted glucose-induced splanchnic and renal vasodilation. In addition, glibenclamide per se induced a decrease in cardiac index. These findings should be taken into account when glibenclamide is administered to patients with cirrhosis and type 2 diabetes.

Type A, but not type B, endothelin receptor antagonists significantly decrease portal pressure in portal hypertensive rats

Background/Aim: Endothelin-1 plays an important role in the regulation of portal hypertension; endothelin antagonists have been extensively studied in portal hypertensive animals. We aimed to evaluate the efficacy of highly selective endothelin antagonists in partial portal vein ligated (PPVL) rats. Methods: Four groups of 7 male Sprague-Dawley rats were administered orally ABT-627 (ET A-selective), A-192621 (ET B-selective), or A-182086 (non-selective), with the fourth group serving as control. On the 3rd day after beginning treatment animals underwent PPVL. On the 11th day hemodynamics were studied and portal vein ET-1 was measured. Results: In the control group portal pressure was 13.4±SD 0.2 mmHg; this increased to 14.9±1.8 ( p<0.05) in the ET B blocked group. In contrast, ET A blockade improved portal hypertension (11.7±1.1, p<0.05), while the treatment with the non-selective antagonist had no effect (12.3±0.7 n.s.). Mean arterial pressure was not significantly affected by any treatment. Portal vein ET-1 was increased in all groups compared to controls; this increase was limited to the pre-stenotic area (79±43 vs 194±76 in the preand post-stenotic portal vein; p<0.0025). Conclusions: Oral administration of an ET A antagonist ameliorated portal hypertension; we suggest that long-term therapy of portal hypertension with selective ET A antagonists may be more beneficial than mixed antagonists.

Pulmonary expression of iNOS and HO-1 protein is upregulated in a rat model of prehepatic portal hypertension.

Portal hypertension is associated with a wide range of pulmonary pathophysiologies, ranging from portopulmonary hypertension to hepatopulmonary syndrome. Although the clinical and pathological features of pulmonary dysfunction in this setting have been extensively characterized, the underlying biology is not well understood. Specifically, the role of mediators that regulate mesenteric vascular hemodynamics in portal hypertension, such as nitric oxide and endothelin, have not been studied in the lung. Using a rat model of prehepatic portal hypertension with preserved hepatic function, we examined pulmonary elaboration of endothelial nitric oxide synthase (NOS), inducible NOS, heme oxygenase- 1 (HO-1), heme oxygenase-2 (HO-2), endothelin-1 mRNA, and protein. In comparison to sham controls, portal hypertensive animals exhibited significantly increased pulmonary iNOS and HO-1 mRNA and protein. Cyclic GMP was significantly increased in portal hypertensive lung tissue, suggesting activation of guanylyl cyclase by the endproducts of iNOS and/or HO-1 activity. Using immunohistochemical analysis, iNOS expression was localized to the vascular endothelium, while HO-1 localized to bronchiolar epithelium and macrophages. These results suggest that production of nitric oxide and carbon monoxide may contribute to the pulmonary pathology associated with portal hypertension.

Portal hypertension increases vasoconstrictor responsiveness of rat aorta

We have examined the effects of pre-hepatic portal hypertension on the responsiveness of aorta from Wistar and Sprague-Dawley rats. Rats were made portal hypertensive by creating a calibrated portal vein stenosis, or sham operated. In rat aorta, there was no significant difference between portal hypertensive and sham-operated animals in the contractile potency of KCl, noradrenaline or phenylephrine. In aortas from Wistar rats, the maximum response to KCl (0.71+/-0.12 g) and noradrenaline (1.00+/-0.17 g) but not phenylephrine (0.86+/-0.10 g) in portal hypertensive animals was significantly increased compared with that in sham-operated animals (0.45+/-0.04 g, 0.57+/-0.07 g, 0.71+/-0.05 g respectively). In aortas from Sprague-Dawley rats, the maximum response to KCl (1. 21+/-0.21 g) and phenylephrine (1.54+/-0.30 g) but not noradrenaline (0.93+/-0.09 g) in portal hypertensive animals was significantly increased compared with that in sham-operated animals (0.59+/-0.09 g, 0.76+/-0.11 g, 1.04+/-0.10 g respectively). There was no difference between portal hypertensive and sham-operated Wistar rats in the affinity or maximum number of binding sites for [3H]prazosin to alpha1-adrenoceptors in cardiac ventricular membranes. It is concluded that portal hypertension tends to produce an increase rather than a decrease in the contractile response to vasoconstrictors in aorta from both Wistar and Sprague-Dawley rats. This suggests that the diminished responsiveness to vasoconstrictors reported in portal hypertensive rats in vivo is not due to a diminished responsiveness at the level of the vascular smooth muscle.

Cardiovascular actions of nitric oxide synthase inhibition in the portal hypertensive rat.

We have investigated the actions of the nitric oxide synthase inhibitor L-NMMA in the portal hypertensive Wistar rat in vivo. Resting blood pressure in the anaesthetised portal hypertensive rat was 107.8+/-11.0 / 79.2+/-11.7 mmHg (n = 12), which was significantly lower than in sham-operated animals (143.0+/-3.8 / 114.0+/-4.0 mmHg, n = 19; P < 0.01). Cardiac output was significantly higher in portal hypertensive (30.2+/-1.0 ml min(-1) per 100 g, n = 12) than sham-operated animals (23.7+/-2.2 ml min(-1) per 100 g, n = 13; P < 0.01). Intravenous injection of L-NMMA (10 mg kg(-1)) significantly increased systemic blood pressure in both portal hypertensive and sham-operated animals to 123.0+/-15.0 / 93.4+/-14.0 mmHg and 162.1+/-5.7 / 131.6+/-6.0 mmHg, respectively. The magnitude of the changes were similar in both groups. This increase in blood pressure was accompanied by a decrease in cardiac output to 88.5+/-2.8% and 91.5+/-2.4% of control in portal hypertensive and sham-operated animals, respectively (no significant difference). L-NMMA (10 mg kg(-1)) had similar effects on small mesenteric arterial conductance in both portal hypertensive and sham operated animals, reducing conductance to 84.4+/-3.6% (n = 6) and 82.7+/-1.2% (n = 4) of control, respectively. It is concluded that L-NMMA has similar effects in vivo in portal hypertensive as compared with sham-operated rats. Hence, an enhancement of endothelium-derived nitric oxide is not involved in the hyperdynamic state following portal hypertension in the rat.

Enhanced cyclooxygenase-1 expression within the superior mesenteric artery of portal hypertensive rats: Role in the hyperdynamic circulation†

Portal hypertension (PHT) is characterized by splanchnic hyperemia due to enhanced production of vasodilator substances. Enhanced vasodilation and increased splanchnic blood flow contribute to the elevated portal pressure characteristic of PHT. The aim of this study was to determine whether cyclooxygenase (Cox) expression is altered in PHT vessels and whether chronic inhibition of this enzyme impacts on splanchnic blood flow in PHT. PHT was created in Sprague-Dawley rats by a partial portal vein ligation. Control animals were sham operated. Plasma 6-keto-PGF1alpha (prostaglandin F1alpha) levels were significantly elevated in PHT after 2 days as compared with sham and remained elevated up to day 15. Treatment with indomethacin (2 mg/kg i.p. daily for 15 days) resulted in a significant decrease in 6-keto-PGF1alpha levels, which was concomitant with a significant decrease in superior mesenteric artery blood flow (Qsma) after 15 days in PHT rats. Cox-I expression was differentially enhanced in the PHT superior mesenteric artery and thoracic aorta during the development and progression of PHT. In contrast, Cox-II messenger RNA (mRNA) and protein expression was not detected in either of these vessels throughout the development of PHT. These data suggest that PHT is associated with enhanced Cox-I expression within the splanchnic vasculature concomitant with elevated plasma prostacyclin levels and a significant pressor response to indomethacin in PHT animals. We conclude that enhanced Cox-I expression results in increased prostacyclin levels that partially contribute to the maintenance of the hyperemia typical of PHT.

A quantitative study on vascular angiotensin II receptors in rats with portal hypertension.

Angiotension-II (A-II) receptor maximal binding capacity (Bmax) and dissociation constants (Kd) of different blood vessels in rats with prehepatic portal hypertension were studied by radioligand binding analysis. The results showed that the A-II receptor Bmax in the thoracic aorta, superior mesenteric artery and portal vein of portal hypertensive animals (113.7 +/- 19.4 fmol/mg protein, 206.9 +/- 39.3 fmol/mg protein and 31.5 +/- 9.2 fmol/mg protein respectively) was all significantly lower than that of controls (146.8 +/- 24.5 fmol/mg protein, 297.2 +/- 44.7 fmol/mg protein and 53.4 +/- 12.1 fmol/mg protein respectively, P < 0.01). The A-II receptor Kd in the superior mesenteric artery was markedly increased in portal hypertensive animals (1.03 +/- 0.11 nmol/L) compared with that in controls (0.88 +/- 0.08 nmol/L, P < 0.05). In the thoracic aorta and portal vein, the A-II receptor Kd in portal hypertensive animals was slightly higher than that in controls, but no significant difference was observed between the two groups. The results suggested that the vascular hyporesponsiveness to A-II in portal hypertension was caused partially by a reduction in number and a decrease in affinity of vascular A-II receptors, and these changes might possibly lead to the formation of hyperdynamic circulation.

Hyposensitivity to nerve stimulation in portal hypertensive rats: role of nitric oxide.

Portal hypertension goes along with vascular hyporeactivity, partly mediated by nitric oxide (NO). Interactions between the adrenergic nervous system and NO in portal hypertension are undetermined. We tested (1) whether superior mesenteric arterial beds of portal hypertensive rats have an altered sensitivity to periarterial nerve stimulation (PNS) and (2) the role of NO in modulating nerve-stimulated responses. Vasopressor responses to PNS (Hz, 2-32) were similar in preparations of partial portal vein-ligated (PVL, n = 12) and control (CON, n = 12) rats (60.0 +/- 6.7 and 47.8 +/- 6.1 CmH2O respectively) for 24 Hz (NS), but sensitivity of vessels of portal hypertensive animals displayed a significant rightward shift [Hz needed for 50% of maximal response (HZ50) being 15.5 +/- 0.4 and 12.9 +/- 0.6 for PVL and CON respectively, P < 0.001]. NO formation inhibition by N omega-nitro-L-arginine (10(-4) mol L-1) significantly increased responses to PNS (P < 0.05), the absolute values for 24 Hz being 101.4 +/- 11.7 cmH2O for PVL (n = 8) and 86.4 +/- 11.4 cmH2O for CON (n = 7) (NS). NO formation inhibition reversed the hyposensitivity in preparations of PVL, Hz50 being 13.9 +/- 0.5 and 13.2 +/- 0.2 for PVL and CON respectively (NS). Adrenergic receptor antagonism with prazosin (10(-7) mol L-1) and yohimbine (10(-6) mol L-1) inhibited PNS-mediated vasopressor reactivity (n = 6 per group, P < 0.001), confirming the nervous origin of vasoconstrictor responses. It is concluded that (1) portal hypertension goes along with a significant hyposensitivity to PNS and (2) this hyposensitivity is reversed by NO-formation inhibition