Circulatory changes induced by portal venous diversion and mesenteric hypertension in rats

Hyperdynamic circulation in portal hypertension: a comparative model of arterio-venous fistula

Complications of portal hypertension remain perplexing physiologic phenomena in the understanding of shunt hemodynamics with multiple theories. Hyperdynamic circulation was also found in sepsis, chronic anemia and arterio-venous (A-V) fistula which relate to an increase in nitric oxide. We hypothesize that portosystemic collaterals may mimic an A-V fistula in which the high-pressure portal blood connects with the lower pressure systemic venous circulation. Although these collaterals decompress the portal circulation, a number of secondary hemodynamic phenomena occur which increase portal blood flow and tend to counteract the portal hypotensive effect of the portosystemic shunt. The consequent increases in cardiac output and portal blood flow perfuse the compromised liver. As portal blood flow increases, collateral flow increases and is nearly totally shunted in the systemic circulation. This shunt may eventually introduce a vicious cycle of hyperdynamic circulation into a compromised host. Ultimately, high-output cardiac failure occurs, leading to cirrhotic cardiomyopathy.

Hyperkinetic circulation and decreased sensitivity to vasoconstrictors following portacaval shunt in the rat. Effects of chronic nitric oxide inhibition

BACKGROUND/AIMS

This study aimed to investigate: (i) whether the hyperkinetic circulation that develops after portacaval shunt is associated with decreased vascular sensitivity to vasoconstrictors and (ii) the role of nitric oxide on its pathogenesis.

METHODS

Portacaval-shunted and sham-operated rats received long-term treatment with the nitric oxide inhibitor L-NAME (osmotic minipump) or its inactive enantiomer D-NAME. Measurements of arterial pressure, cardiac output and superior mesenteric artery blood flow (transit-time flow probe) were done 4 days later in baseline conditions and after increasing doses of methoxamine. Peripheral and superior mesenteric vascular resistance were calculated.

RESULTS

Portacaval shunted rats showed a significantly lower peripheral and superior mesenteric vascular resistance and a significant reduction in their response to incremental doses of methoxamine than sham-operated controls. Chronic nitric oxide inhibition attenuated the systemic but not the splanchnic vasodilatation and totally corrected the hyposensitivity to methoxamine of portacaval-shunted rats. However, they still had a significantly lower peripheral and superior mesenteric vascular resistance than sham-operated rats.

CONCLUSIONS

This study shows that the splanchnic and systemic hyporesponsiveness to methoxamine observed in portacaval-shunted rats could be explained by an excess of nitric oxide. However, other factors may be involved in maintaining splanchnic and systemic vasodilatation despite NO-inhibition.

Effects of portacaval shunting on hyperdynamic circulation in bile duct-ligated cirrhotic rats

BACKGROUND/AIMS

Liver cirrhosis and portal hypertension are associated with hyperdynamic circulation. Portacaval shunts are widely used to prevent recurrent hemorrhage, but the hemodynamic effects caused by these procedures have not been well characterized in cirrhosis. We therefore compared the hemodynamic effects of both end-to-side and side-to-side portacaval shunts in normal and cirrhotic rats.

METHODS

Sprague-Dawley rats were divided into six groups according to the operations they underwent. End-to-side or side-to-side portacaval shunts were performed in both rats with cirrhosis induced by bile duct ligation and sham-operated rats. Systemic and regional blood flows were measured by the radioactive microsphere method.

RESULTS

Portal pressures in the shunted rats decreased significantly. Cardiac index in cirrhotic rats (557 +/- 27 ml.min-1.kg-1) was significantly higher than controls (455 +/- 21 ml.min-1.kg-1), but the two types of shunts did not further increase cardiac index in either the cirrhotic or the sham-operated rats. After shunting, hepatic arterial flows approximately doubled. Portal tributary blood flows in the end-to-side shunted sham (108 +/- 13 ml.min-1.kg-1) and cirrhotic (139 +/- 19 ml.min-1.kg-1 groups were significantly higher than their respective controls (62 +/- 8 and 76 +/- 5 ml.min-1.kg-1). Portosystemic shunting indices were > 99% in both the end-to-side and side-to-side shunted groups in cirrhotic and sham-operated rats.

CONCLUSIONS

The hyperdynamic circulation in cirrhotic rats was not augmented by portacaval shunting operations (either end-to-side or side-to-side), despite essentially total portosystemic blood diversion. Compensatory increase in the hepatic arterial blood flow to the liver remained intact even in cirrhotic rats. A selective redistribution of cardiac output to the mesenteric vascular bed was observed after the shunting procedure. However, there were no significant differences in hemodynamics between the end-to-side and side-to-side shunted groups.

Transjugular intrahepatic portosystemic shunts: comparison with paracentesis in patients with cirrhosis and refractory ascites: a randomized trial. French Group of Clinicians and a Group of Biologists

BACKGROUND/AIMS

Transjugular intrahepatic portosystemic shunts reduce portal pressure and can control ascites in patients with cirrhosis. We carried out a controlled study to evaluate this procedure for the management of refractory ascites in patients with cirrhosis and to clarify its mechanism of action.

METHODS

Twenty-five patients with refractory ascites were included in the trial; 13 were randomly assigned to shunts and 12 to paracentesis. Four patients in each group were Child-Pugh class C and the others were class B. Follow-up ranged from 9 to 34 months. Hemodynamic values, liver and renal tests and neurohumoral factors were measured before and at 4 months after inclusion.

RESULTS

Shunts were successfully placed in 10 out of 13 patients. At 4 months, ascites had improved in all class B patients in the shunt group and in none of the patients in the paracentesis group (p < 0.05); ascites did not improve in any of the class C patients in either of the groups. At 2 years, the overall survival rate was 29 +/- 13% (mean +/- SE) in the shunt group and 56 +/- 17% in the paracentesis group (p < 0.05). In class B patients, there was no significant difference in mortality. At 4 months, portal pressure was significantly lower than before the shunt, while plasma levels of atrial natriuretic peptide were significantly higher and plasma levels of renin and norepinephrine significantly lower.

CONCLUSIONS

In this trial, intrahepatic shunts were effective on refractory ascites in patients with cirrhosis. However, the overall survival rate was lower in shunted patients than in those treated with paracentesis. The efficacy of intrahepatic shunts on ascites was only observed in class B patients. Survival did not improve in class B patients, and decreased in class C patients compared to paracentesis. The efficacy of shunts on ascites might be due to neurohumoral factors which control natriuresis and depend on hepatic sinusoidal pressure.

Effects of portal vein stenosis and superior mesenteric vein ligation on mesenteric venous pressure and porta-systemic shunting in the rat

We studied the relative contributions of splanchnic congestion and porta-systemic shunting to the maintenance of experimental portal venous hypertension. Three groups of rats were prepared: portal vein-stenosed, superior mesenteric vein-ligated and sham operated. Though elevated in both operated groups compared to controls, mesenteric venous pressure was highest in the portal vein-stenosed animals (PV vs SMV vs Sham: 19.6 +/- 1.3 vs 15.6 +/- 0.7 vs 13 +/- 0.6; p < .05 PV and SMV vs Sham, and PV vs SMV) despite the presence of 50% porta-systemic shunting in the portal vein-stenosed animals. Shunting was negligible in the other two groups. Peripheral plasma glucagon and vasoactive intestinal peptide (VIP) levels were similar in all three groups. We conclude that mesenteric congestion alone plays a minor role in the pathogenesis of portal hypertension, which may instead be related to the porta-systemic shunting of vasoactive substances other than glucagon and VIP.