Vascular nitric oxide production during the development of two experimental models of portal hypertension

doi:10.1016/S0168-8278(99)80145-7

Journal of Hepatology

Volume 30, Issue 5, May 1999, Pages 896-903

https://doi.org/10.1016/S0168-8278(99)80145-7 Get rights and content

Abstract

Background/Aims: The aim of this study was to determine the relative roles of constitutive NOS (NOS3) and inducible NOS (NOS2) isoforms during the development of two models ofportal hypertension in rats.

Methods: Vascular reactivity of aortic rings for norepinephrine was performed in control, sham-operated, portal-vein-stenosed and secondary biliary cirrhotic rats 1, 4, 7, 14 and 28 days after surgery. NOS activity and nitrate plasma levels were also measured.

Results: An impaired response to norepinephrine observed in sham-operated, portal-vein-stenosed and cirrhotic rats at days 1 and 4 compared with controls was reversed after L-NNA and aminoguanidine. Portal hypertensive rats remained hyporeactive at days 7, 14 and 28 compared with sham-oprated rats. At days 7 and 14 in portal-vein-stenosed rats, vascular hyporeactivity was reversed by L-NNA and W7. At days 14 and 28 in cirrhotic rats, vascular hyporeactivity was reversed by L-NNA and W7. Nitrate levels increased at day 1 in the 3 groups, and increased at days 14 and 28 in portal hypertensive rats. Total NOS-activity increased in cirrhotic rats at day 28, in portal-vein-stenosed rats at day 14, and in sham-operated rats at day 1 compared to controls. NOS2 activity increased only in sham-operated rats at day 1.

Conclusions: This study shows that for two models of portal hypertension, increased NO production in the first days is related to NOS2 induction secondary to surgery. On the other hand, when portal hypertension has fully developed, the NOS3 isoform appears to play the major role.

Section snippets

Animals

One hundred and sixteen male Sprague-Dawley rats (Charles River Laboratories, Saint-Aubin-lès-Elbeuf, France) were used in the present study. The animals were divided into 4 groups. The first group included 18 normal rats (control group). The second group included 34 rats in which a sham operation was performed (sham group) under pentobarbital anesthesia. In sham-operated animals, the portal vein and the main bile duct were isolated but no ligature was placed. The third group included 29 rats

Vascular reactivity

No significant differences were observed between control, sham-operated, portal-vein-stenosed and bileduct-ligated rats with respect to body weight or length and diameter of aortic rings at the different time-points.

Experiment 1: dose-response curves to norepinephrine. Cumulative dose-response curves to NE are shown in Fig. 1. At day 1 and 4 after surgery, an impaired response to NE was observed in sham-operated, portal-vein-stenosed and bile-duct-ligated rats compared with control rats (Table

Discussion

In portal hypertension, increased production of NO seems to account, in part, for systemic and splanchnic vasodilation, for the hyporeactivity to certain endogenous vasoconstrictors 2., 3. and for water excretion in cirrhosis (31). However, the NOS isoform responsible for NO overproduction, and the mechanisms which cause the activation and/or induction of this enzyme, have not yet been clearly established. The identification of this isoform could be useful in understanding the pathophysiology

Acknowledgements

Presented in part at the 47th Annual Meeting of the American Association for the Study of Liver Diseases, Chicago 8–12 November 1996 and published in abstract form (Hepatology 1996; 24: 314A).

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Citation Excerpt :
The temporal relationship to the insult leading to portal hypertension appears to play a major role. Thus, in portal vein ligation there is an early upregulation of iNOS, probably related to surgery; whereas later on, induction of ecNOS appears to play a major role.98 Countering the sole role of ecNOS in the development of the hyperdynamic circulation syndrome is the fact that ecNOS knockout mice develop portal hypertension and hyperdynamic circulation to a similar extent as wild-type animals.99
Increased understanding of the hyperdynamic circulation syndrome has resulted in novel therapeutic approaches, some of which have already reached clinical practice. Central to the hyperdynamic circulation syndrome is an imbalance between the increase in different vasodilators (foremost among which is nitric oxide) and the compensatory increase in vasoconstrictors—usually accompanied by a blunted response. This chapter discusses the role of endothelin in the pathogenesis of the syndrome and in future treatment approaches. A relatively new area of research in this field is the role of infection and inflammation in the initiation and maintenance of the hyperdynamic circulation syndrome. The use of antibiotics in the setting of acute variceal bleeding is standard practice. Studies have suggested that chronic manipulation of the intestinal flora could have beneficial effects in the treatment of portal hypertension. The bile salts are another novel and interesting target. Although their vasoactive properties have been known for some time, recent data demonstrate that their effects could be central in the pathogenesis of the hyperdynamic circulation syndrome, and that manipulation of the composition of the bile acid pool could be a therapeutic approach to portal hypertension. Finally, hypoxia and angiogenesis play a role in the development of portal hypertension and the formation of collaterals. This role needs to be further defined but it appears likely that this phenomenon is yet another target for therapeutic intervention.
Time-dependent reduction of acetylcholine-induced relaxation in corpus cavernosum of cholestatic rats: Role of nitric oxide and cyclooxygenase pathway
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The endothelium-dependent relaxation of corpus cavernosum smooth muscle and the roles of nitric oxide (NO) and arachidonic acid products of cyclooxygenase were investigated in non-operated, SHAM-operated, and bile duct-ligated rats. We further investigated the time-dependent alterations of corpus cavernosum relaxation in 2-, 7-, and 14-day bile duct-ligated animals. Acetylcholine produced concentration-dependent relaxation in phenylephrine-precontracted strips of corpus cavernosum. A significant reduction in the acetylcholine-induced relaxation was observed 2 days after bile duct ligation, and a greater reduction was observed on subsequent days. Incubation with 20 μM indomethacin reduced the acetylcholine-induced relaxation of the corpus cavernosum of unoperated rats while it had no effect in the corpus cavernosum of bile duct-ligated rats. Chronic treatment with N^ω-Nitro-l-Arginine Methyl Ester (L-NAME, 3 mg/kg/day, intraperitoneally) reduced the relaxation responses in the unoperated group while it had no effect in the bile duct-ligated group. These results show that acetylcholine-induced corporal relaxation is impaired in cholestatic rats, and this may be related to deficient nitric oxide production by the endothelium. The involvement of prostaglandins in this impairment seems unlikely.
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Portal hypertension induces neuroendocrine activation and a hyperkinetic circulation state. This study investigated the consequences of portal hypertension on heart structure and function. Intrahepatic portal hypertension was induced in male Sprague-Dawley rats by chronic bile duct ligation (CBDL). Six weeks later, CBDL rats showed higher plasma angiotensin-II and endothelin-1 (P < .01), 56% reduction in peripheral resistance and 73% reduction in pulmonary resistance (P < .01), 87% increase in cardiac index and 30% increase in heart weight (P < .01), and increased myocardial nitric oxide (NO) synthesis. In CBDL rats, macroscopic analysis demonstrated a 30% (P < .01) increase in cross-sectional area of the left ventricular (LV) wall without changes in the LV cavity or in the right ventricle (RV). Histomorphometric analysis revealed increased cell width (12%, P < .01) of cardiomyocytes from the LV of CBDL rats, but no differences in myocardial collagen content. Myocytes isolated from the LV were wider (12%) and longer (8%) than right ventricular myocytes (P < .01) in CBDL rats but not in controls. CBDL rats showed an increased expression of ANF and CK-B genes (P < .01). Isolated perfused CBDL hearts showed pressure/end-diastolic pressure curves and response to isoproterenol identical to sham hearts, although generated wall tension was reduced because of the increased wall thickness. Coronary resistance was markedly reduced. This reduction was abolished by inhibition of NO synthesis with N-nitro-L-arginine. Expression of eNOS was increased in CBDL hearts. In conclusion, portal hypertension associated to biliary cirrhosis induces marked LV hypertrophy and increased myocardial NO synthesis without detectable fibrosis or functional impairment. This observation could be relevant to patients with cirrhosis. (Hepatology 2003;38:589-598.)
The role of nitric oxide synthase isoforms in extrahepatic portal hypertension: Studies in gene-knockout mice
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Considerable debate exists concerning which isoform of nitric oxide synthase (NOS) is responsible for the increased production of NO in PHT. We used the portal vein ligation model of PHT in wild-type and eNOS- or iNOS-knockout mice to definitively determine the contribution of these isoforms in the development of PHT.
The portal vein of wild-type mice, or those with targeted mutations in the nos2 gene (iNOS) or the nos3 gene (eNOS), was ligated and portal venous pressure (Ppv), abdominal aortic blood flow (Qao), and portosystemic shunt determined 2 weeks later.
In wild-type mice, as compared with sham-operated controls, portal vein ligation (PVL) resulted in a time-dependent increase in Ppv (7.72 ± 0.37 vs 17.57 ± 0.51 cmH₂O, at 14 days) concomitant with a significant increase in Qao (0.12 ± 0.003 vs 0.227 ± 0.005 mL/min/g) and portosystemic shunt (0.47% ± 0.01% vs 84.13% ± 0.09% shunt). Likewise, PVL in iNOS-deficient mice resulted in similar increases in Ppv, Qao, and shunt development. In contrast, after PVL in eNOS-deficient animals, there was no significant change in Ppv (7.52 ± 0.22 vs 8.07 ± 0.4 cmH₂0) or Qao (0.111 ± 0.01 vs 0.14 ± .023 mL/min/g). However, eNOS (−/−) mice did develop a substantial portosystemic shunt (0.33% ± 0.005% vs 84.53% ± 0.19% shunt), comparable to that seen in wild-type animals after PVL.
These data support a key role for eNOS, rather than iNOS, in the pathogenesis of PHT.
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The role of nitric oxide (NO) in portal hypertension is poorly understood. The role of NO upon hepatic arterial and portal venous vasoconstrictor responses to noradrenaline and ATP in rats with secondary biliary cirrhosis was evaluated. Cirrhosis was induced by bile duct ligation after which livers were excised and dual-perfused in vitro. Concentration-dependent dose–response curves were then constructed to hepatic arterial and portal venous noradrenaline and ATP. Hepatic arterial responses to noradrenaline and ATP were significantly attenuated in cirrhotic rats. 100 μM N^G-nitro-l-arginine methyl ester (l-NAME) restored attenuated hepatic arterial responses to noradrenaline and ATP in cirrhotic rats. Portal venous responses to noradrenaline in cirrhotic rats were significantly increased compared to controls and were not affected by l-NAME. However, portal venous responses to ATP were significantly attenuated in cirrhotic rats and were also not restored by l-NAME. Hepatic arterial or portal venous responses to noradrenaline did not change after infusion of l-NAME. Hepatic arterial responses to noradrenaline and ATP were significantly attenuated in cirrhotic rats, possibly due to increased production of NO. However, portal venous responses in cirrhotic rats were increased to noradrenaline and attenuated to ATP, and were not related to increased NO production.

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Vascular nitric oxide production during the development of two experimental models of portal hypertension

Abstract

Section snippets

Animals

Vascular reactivity

Discussion

Acknowledgements

J Hepatol

J Biol Chem

Biochem Biophys Res Comm

FEBS Lett

FEBS Lett

J Hepatol

Gastroenterology

Eur J Pharmacol

Gastroenterology

J Hepatol

Hepatology

Gastroenterology

J Hepatol

Hepatology

Lancet

Immunol Med Microbiol

Gastroenterology

J Hepatol

Hepatology

Pharmacol Ther

Hyperdynamic circulation of liver disease 40 years later: pathophysiology and clinical consequences

Hepatology

The nitric oxide hypothesis and the hyperdynamic circulation in cirrhosis

Hepatology