The arginine-nitric oxide pathway in thrombotic microangiopathy.

Eleven patients with thrombotic thrombocytopenic purpura (TTP) or haemolytic uremic syndrome (HUS) were investigated with respect to plasma concentrations of L-arginine, a substrate for nitric oxide (NO) and asymmetrical dimethyl arginine (ADMA), during active disease and after recovery. Plasma concentration of NO3-, the degradation product of NO, was also analyzed. The patients were treated with fresh-frozen plasma and plasmapheresis. One of the patients had experienced relapses of TTP five times during the preceding year. After treatment with p.o. arginine hydrochloride 1.5 g x 3 was started, no relapse has occurred during a 12-month period. During the active phase the plasma concentration of arginine was low and that of NO3- was very high, indicating a high NO-synthesis rate. The arginine concentration normalized on recovery. Plasma levels of ADMA, was twice normal during active disease, and did not return to normal on recovery. In conclusion, patients with TTP/HUS exhibit signs of activation of the NO-synthesis.