Inhibitory role of capsaicin-sensitive afferent neurons and nitric oxide in hemostasis.

Capsaicin-sensitive afferent neurons control blood flow via release of peptide transmitters and formation of nitric oxide (NO). The present study examined whether capsaicin-sensitive afferent neurons and NO interact in the control of hemostasis. Afferent nerve ablation by pretreating rats with a neurotoxic dose of capsaicin (125 mg/kg) led to a 26% reduction of the time of bleeding from punctured small mesenteric arteries in pentobarbital-anesthetized animals. Blockade of NO formation by NG-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg) attenuated the bleeding time in capsaicin-pretreated rats but had no effect in vehicle-pretreated rats. Platelet aggregation induced by ADP was significantly augmented by 12% in capsaicin-pretreated rats. L-NAME did not alter platelet aggregation in vehicle-pretreated rats but enhanced it in capsaicin-pretreated animals. The prothrombin and partial thromboplastin time and the plasma levels of fibrinogen and antithrombin III remained unchanged by capsaicin or L-NAME, whereas the thrombin time was reduced in capsaicin-pretreated rats. These data indicate that capsaicin-sensitive afferent neurons play an inhibitory role in platelet aggregation and hemostasis, a function in which they interact with the NO system.