Asymmetric Dimethylarginine To the Editor: Kielstein et al1 describe the effects of the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine (ADMA), in humans in vivo but do not make reference to two previous human studies.2,3 In the original paper describing the presence of ADMA in human plasma and its accumulation in chronic renal failure, Vallance et al2 also described the...