Hyperammonemia inhibits platelet aggregation in rats

The effect of hyperammonemia on ex vivo platelet function and in vivo nitric oxide synthesis was evaluated in rats. In addition, mitochondrial energy production was assessed from the fluorescence intensity of tetramethylrhodamine ethyl ester (TMRE). Continuous ammonium acetate infusion significantly reduced ex vivo platelet aggregation concomitant with a decrease of the platelet cytoplasmic ATP level. The serum level of L-arginine, as well as the levels of nitrite and nitrate (oxidative by-products of nitric oxide), increased with ammonium infusion. Prior administration of N omega-nitro-L-arginine methyl ester, a competitive inhibitor of nitric oxide synthase, did not affect the ammonia-induced rise in L-arginine, but substantially attenuated the associated decrease of platelet ATP and TMRE fluorescence as well as diminishing the anti-aggregatory effect of ammonia infusion. These findings suggest that the synthesis of nitric oxide from L-arginine is accelerated by continuous ammonium infusion and inhibits ex vivo platelet aggregation in the rat, probably by reducing mitochondrial energy production.