Splanchnic hyposensitivity to glypressin in a hemorrhage-transfused common bile duct-ligated rat model of portal hypertension: role of nitric oxide and bradykinin.

BACKGROUND/AIMS: The portal hypotensive effect of vasopressin during hemorrhage is less effective than that during stable condition in cirrhotic patients or experimental portal hypertension (the so-called hyposensitivity phenomenon). Recent studies have demonstrated that constitutive nitric oxide activities and bradykinin in hemorrhage-transfused partially portal vein-ligated rats are responsible, at least partly, for the splanchnic hyposensitivity to glypressin (a long acting vasopressin analogue). This study investigated the relative contribution of nitric oxide synthase isoforms and the role of bradykinin in the pathogenesis of splanchnic hyposensitivity in rats with cirrhosis induced by common bile duct-ligation (BDL).

METHODOLOGY

Five weeks after BDL, systemic and portal hemodynamics were measured in stable or bleeding BDL rats receiving intravenous infusion of glypressin (0.2 mg/kg). In the treatment groups, N(G)-nitro-L-arginine methyl ester (L-NAME, a non-selective nitric oxide synthase inhibitor), L-canavanine (a specific inducible nitric oxide synthase inhibitor) or HOE 140 (a bradykinin B2 receptor antagonist) was administered 45 minutes before the infusion of glypressin. In rats with a hypotensive hemorrhage, 4.5 ml of blood was withdrawn and 50% of the withdrawn blood was reinfused before the administration of glypressin or various inhibitors.

RESULTS

Splanchnic hyposensitivity to glypressin was demonstrated in the hemorrhage-transfused BDL rats. The infusion of L-NAME elevated the mean arterial pressure in the bleeding BDL rats without the modulation of portal pressure. The addition of L-NAME or HOE 140, but not L-canavanine, significantly and similarly potentiated the portal-hypotensive effects of glypressin.

CONCLUSIONS

Constitutive nitric oxide synthase and bradykinin play major roles in the development of splanchnic hyposensitivity to glypressin observed in hemorrhage-transfused rats with biliary cirrhosis.