Chronic administration of propylthiouracil ameliorates hyperdynamic circulation in portal hypertensive rats

OBJECTIVE

To evaluate the effect of a hypothyroid state, induced by chronic propylthiouracil administration, on splanchnic and systemic hemodynamic parameters in rats with portal hypertension due to portal vein ligation.

METHODS

Portal hypertension was induced by surgical stenosis of the portal vein. Cardiac index and portal blood flow were measured using radioactive microspheres. Measurements were performed after treatment with propylthiouracil (1 mg/ml in drinking water) for 5 days.

RESULTS

Propylthiouracil-treated portal hypertensive rats had a lower portal pressure (12.4 +/- 1.9 versus 16.3 +/- 0.7 mmHg; p < 0.05) and portal blood flow (11.6 +/- 0.7 versus 13.2 +/- 1.3 ml/min/100 g; p < 0.05) than non-treated animals. Splanchnic vasoconstriction in treated animals was associated with a higher peripheral vascular resistance (2.3 +/- 0.4 versus 1.8 +/- 0.3 mmHg/ml/min/100 g; p < 0.05) than controls.

CONCLUSION

These results suggest that portal pressure can be lowered by inducing a hypothyroid state by chronic administration of propylthiouracil.

Nitric oxide synthase activity in the splanchnic vasculature of patients with cirrhosis: relationship with hemodynamic disturbances

BACKGROUND/AIMS

It has been demonstrated that an overproduction of nitric oxide plays an important role in the pathogenesis of the hyperdynamic circulation exhibited by cirrhotic patients. Nevertheless, evidence is supported by studies performed in experimental models or by indirect measurements in humans. The purpose of this study has been to evaluate nitric oxide production in splanchnic vasculature of patients with cirrhosis and to investigate its possible relationship with systemic and splanchnic hemodynamics.

METHODS

Nitric oxide synthase (NOS) activity was measured in hepatic artery and portal vein tissues of nine cirrhotic patients. Samples were obtained during liver transplantation. Control samples were obtained simultaneously from the corresponding tissues of the liver donors. Hemodynamic parameters were determined with Doppler ultrasonography.

RESULTS

NOS activity was significantly higher in hepatic artery of cirrhotic patients than in controls (8.17 +/- 1.30 vs 4.57 +/- 0.61 pmoles/g of tissue/min, P < 0.05). Patients with ascites showed a higher hepatic artery NOS activity than patients without ascites. Highly significant correlation was observed between cardiac output and hepatic artery NOS activity as well as between portal blood flow and hepatic artery NOS activity.

CONCLUSIONS

The present study demonstrates an enhanced production of nitric oxide in the splanchnic vasculature of patients with cirrhosis.

[Dexamethasone, an inhibitor of the expression of inducible nitric oxide synthase, does not modify the hyperdynamic state in cirrhotic rats]

Increased nitric oxide formation has been shown to be involved in the hyperdynamic circulation of portal hypertension. It has been proposed that it could be related to stimulation of the inducible nitric oxide synthase by endotoxin. Therefore, the aim of the present study was to evaluate whether dexamethasone treatment, an inhibitor of the expression of the inducible enzyme, ameliorates the hyperdynamic circulation observed in cirrhotic rats due to chronic bile duct ligation. Systemic and splanchnic hemodynamic parameters were measured after administration of dexamethasone (3 mg/kg/day during 3 days, i.p.) or its vehicle. In cirrhotic rats dexamethasone treatment caused a mild but not significantly higher mean arterial pressure in comparison with vehicle while similar values of cardiac output, peripheral vascular resistance, portal blood flow and portal pressure were observed in both group of animals. A significant body weight loss over the three days of treatment was observed in rats receiving dexamethasone. In sham-operated rats, dexamethasone administration caused similar changes as observed in cirrhotic animals. Endotoxemia was observed in five of six cirrhotic rats while it was not detected in the control group. Our results show that dexamethasone administration does not modify systemic and splanchnic hemodynamic parameters in endotoxemic cirrhotic rats. This finding suggests that stimulation of the inducible nitric oxide synthase may not play a role in the increased nitric oxide production in portal hypertension.

Prolonged bleeding time in experimental cirrhosis: role of nitric oxide

BACKGROUND/AIMS

Nitric oxide is a powerful in vitro inhibitor of platelet adhesion and aggregation. Our aim was to investigate whether the in vivo inhibition of nitric oxide release shortens bleeding time, in rats with cirrhosis induced by chronic bile duct ligation.

METHODS

Mean arterial pressure and bleeding time were measured under basal conditions and 5, 15 and 30 min after administration of vehicle (0.9% saline) or an inhibitor of nitric oxide synthesis, Nw-nitro-L-arginine (5 mg/kg, iv). Mean arterial pressure was measured with an intra-arterial catheter and bleeding time with a standardized Simplate device.

RESULTS

Cirrhotic rats showed a lower mean arterial pressure (116+/-4 mmHg) and a prolonged bleeding time (177+/-40 s) compared to control animals (133+/-6 mmHg and 95+/-12 s, respectively, p<0.01). In cirrhotic rats, Nw-nitro-L-arginine significantly increased mean arterial pressure (from 116+/-5 to 141+/-11 mmHg, p<0.05) and completely normalized bleeding time (from 170+/-39 to 103+/-21 s, p<0.05) 15 min after administration. Pretreatment with L-arginine (300 mg/kg, iv) prevented the hemodynamic and hemostatic changes induced by Nw-nitro-L-arginine. A trend to normalize platelet adhesion was observed in cirrhotic rats after the inhibition of nitric oxide production. In control animals, Nw-nitro-L-arginine increased mean arterial pressure, while no effect on bleeding time was observed.

CONCLUSIONS

These findings support the concept that nitric oxide may be a mediator in the bleeding time abnormalities associated with experimental cirrhosis.

Von Willebrand factor could be an index of endothelial dysfunction in patients with cirrhosis: relationship to degree of liver failure and nitric oxide levels

BACKGROUND/AIMS

The aim of this study was to evaluate the relationship between plasma levels of von Willebrand factor (vWF), a marker of endothelial cell activation, and nitric oxide, a powerful vasodilator synthesized by endothelial cells, in 27 patients with cirrhosis at different stages of the disease. These results were compared with those of age-matched normal, healthy subjects (n=10).

METHODS

vWF:antigen was measured by electro-immunodiffusion test and serum nitrite and nitrate levels, the stable end products of nitric oxide metabolism, were determined by an enzymatic procedure.

RESULTS

vWF:antigen and nitrite/nitrate levels were significantly higher in cirrhotic patients (367+/-185% and 29.3+/-10.8 micromol/l) than in healthy subjects (92+/-20% and 19.2+/-8.3 micromol/l, p<0.05, respectively). Higher levels of vWF:antigen and nitrites/nitrates were observed in patients with more advanced degrees of liver failure, as reflected by quantitative Child-Pugh's score (516+/-154% and 38.3+/-7.8 micromol/l in Child-Pugh > or = 9 vs 227+/-61% and 21.0+/-6.1 micromol/l in Child-Pugh <9, p<0.001, respectively). Moreover, both endothelial-related factors were higher in patients with ascites than those without ascites (543+/-158% and 37.8+/-8.9 micromol/l vs 262+/-103% and 24.4+/-8.8 micromol/l, p<0.001, respectively). In the overall series, a highly significant linear correlation between nitrites/nitrates and vWF:antigen levels was observed in patients with cirrhosis (r=0.79, p<0.001).

CONCLUSIONS

These results support a cirrhosis-related endothelial dysfunction and suggest that plasma vWF measurement could be useful as a marker of endothelial disturbance in patients with cirrhosis.

Hemostatic and hemodynamic effects of vasopressin analogue DDAVP in patients with cirrhosis

Desmopressin (DDAVP), a synthetic analogue of vasopressin, has been shown to improve the bleeding time in patients with cirrhosis. The duration of this effect and the hemodynamic changes associated with DDAVP have not been studied so far. To evaluate these issues, 14 cirrhotics with portal hypertension were studied in basal conditions and after DDAVP (0.3 uk/kg). In 8 patients, hemostatic tests were done at basal conditions and 1, 3, 6 and 24 hs after drug administration. In the remaining 6 patients, mean arterial pressure, cardiac output, portal and femoral blood flows were evaluated. Hemodynamic parameters were measured by Doppler ultrasound. DDVP caused a marked decrease in bleeding time at 1, 3, 6 and 24 hs (14 +/- 9 vs 8 +/- 3, 7 +/- 4, 6 +/- 4 and 8 +/- 4 min, respectively); the decrease was maximal and statistically significant at 6 hs (55 +/- 15%, p < 0.02) after DDAVP infusion. Bleeding time reduction was observed in every patient studied. In the hemodynamic study, DDAVP caused a mild but significant decrease in mean arterial pressure (12 +/- 8%, p < 0.05); no significant changes were observed in the rest of hemodynamic parameters studied. These findings show that DDAVP can be used to shorten the bleeding time for a period of at least 24 hs in patients with cirrhosis, without deleterious hemodynamic effects. This beneficial effect may be of potential relevance in the medical management of patients with chronic liver diseases.

Daily variation in portal blood flow and the effect of propranolol administration in a randomized study of patients with cirrhosis

A nocturnal increase in portal pressure and blood flow was demonstrated in patients with cirrhosis, suggesting that these hemodynamic changes may contribute to the triggering of the hemorrhagic episodes observed during the night in these patients. It is known that propranolol reduces portal flow, thus reducing the risk of variceal bleeding. In a double-blind, placebo-controlled study, we evaluated the effect of long-term propranolol administration on the daily fluctuation of systemic and splanchnic hemodynamic parameters in 14 patients with cirrhosis. Cardiac output and portal blood flow were measured by the Doppler technique. A daily fluctuation of both cardiac output and portal blood flow was observed, peaking at midnight. beta-Adrenergic blockade was manifested by a significant reduction in heart rate (-21% +/- 4%, P < .01) and cardiac output (-12% +/- 2%, P < .05). A significant decrease in portal blood flow (-20% +/- 4%, P < .01) was also observed in these patients. Propranolol administration blunted the time-related changes in cardiac output and portal blood flow. In contrast, patients receiving placebo had a nocturnal peak of both parameters similar to that observed under basal conditions. Our study shows that chronic propranolol administration abolishes the nocturnal peak of portal blood flow in patients with cirrhosis and indicates a preventive effect of propranolol in these patients.

Pentoxifylline, a drug with rheological effects, decreases portal pressure in an experimental model of cirrhosis

OBJECTIVE

To evaluate the influences of blood viscosity changes, mediated by a haemorheological agent, on splanchnic and systemic haemodynamic parameters in rats with cirrhosis due to chronic bile duct ligation.

METHODS

Blood viscosity was measured using a cone-plate viscometer and whole blood filterability was determined by a filtration method. Cardiac index and portal venous inflow were measured using radioactive microspheres. Measurements were performed 30 min after double-blind administration of placebo or pentoxifylline (25 mg/kg, intravenously).

RESULTS

As compared with placebo, pentoxifylline-treated cirrhotic rats had a lower portal pressure (13.8 +/- 1.4 vs. 12.1 +/- 1.6 mmHg, P < 0.05) and blood viscosity at shear rates of 115/s (6.6 +/- 0.8 vs. 5.8 +/- 0.3 mPas, P < 0.05), associated with an improvement of whole blood filterability (45.0 +/- 12.9 vs. 20.0 = 3.9 s/ml, P < 0.01). Similar values of mean arterial pressure, cardiac index and portal venous inflow were observed in both groups. A significant correlation was found between portal pressure and blood viscosity at a shear rate of 115/s (r = 0.71, P < 0.01).

CONCLUSION

These results suggest that portal pressure can be modified by pentoxifylline in an experimental model of cirrhosis. These haemodynamic changes are associated with a lower blood viscosity and whole blood filterability. Pentoxifylline may be a new approach in the treatment of portal hypertension.