Changes of L-arginine-NO pathway in platelets of microvascular angina patients and reversing effects of intravenous L-arginine infusion on L-Arg-NO transport

Objective:To observe the L-Arg(L-arginine)transport,the nitric oxide(NO)production,and NO synthase(NOS)activity in platelets,investigate the significance of the L-Arg-NO system in the pathogenesis of microvascular angina(MVA),and to study the reversing effects of intravenous L-Arg infusion on L-Arg transport.Methods:The 3H-L-Arg transport,NO production,and NOS activity in platelets were examined in 15 patients with MVA and 15 healthy controls.The 15 patients were given intravenous L-Arg infusion(20 g/d)after basic physical examination and were examined again 10 days later.Results:The L-Arg transport in platelets of MVA patients was obviously lower than that in the normal group;the maximum transport velocity(Vmax)decreased by 34.4% compared with the normal group(P0.01);and the Michaelis constant(Km)increased by 21.4%(P0.05).The production of NO-2 and the activity of NOS in platelets were decreased by 47.1%(P0.05)and 25.4%(P0.05)compared with the normal group,respectively.Intravenous L-Arg infusion reversed the above changes in MVA patients;it increased the Vmax by 11.9%(P0.01)and decreased Km by 18%(P0.05);it also increased production of NO-2 by 1.33 folds(P0.05)and NOS activity by 1.2 folds(P0.05).Especially,the attack of angina and patient ECG were greatly improved after intravenous L-Arg infusion.Conclusion:L-Arg-NO pathway is impaired in MVA patients,which might be responsible for the endothelium-dependent vascular relaxation in MVA patients.Intravenous L-Arg infusion may benefit the impaired function of L-Arg-NO transport in patients with MVA.