Evidence that endogenous nitric oxide modulates plasma fibrinogen levels in the rat.

This study investigated the effect of prolonged inhibition of nitric oxide (NO) synthase on plasma fibrinogen levels and platelet count in the rats. NG-nitro-L-arginine methyl ester (L-NAME), when administered orally twice a day, at 10-100 mg kg-1, for 7 consecutive days, 14 times in all, significantly elevated fibrinogen levels and systolic blood pressure in a dose-dependent manner. The same dose range of L-NAME failed to alter platelet count and plasma protein concentrations. The increase in fibrinogen levels produced by chronic treatment with L-NAME at 30 mg kg-1 was reversed by L-arginine at 500-1500 mg kg-1 in a dose-dependent manner. These findings suggest that endogenous NO tonically acts to reduce plasma fibrinogen levels in rats under physiological conditions.