Prolonged bleeding time in experimental cirrhosis: role of nitric oxide

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.

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.

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.

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