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To the Editor: The study by Dr Morris and colleagues¹ indicates that a reduction in arginine availability may play a role in pulmonary hypertension and mortality in patients with SCD. The authors provide evidence that in these patients, hemolysis increases circulating levels of arginase, explaining the decline in plasma arginine and the increase in plasma ornithine levels. This derangement in arginine metabolism is associated with pulmonary hypertension and with mortality in patients with SCD. L-Arginine is the precursor of NO, and a reduction in its plasma levels could explain the endothelial vasodilator dysfunction and pulmonary hypertension that occurs in these patients.

However, there are 2 other potential causal explanations to consider. First, hemolysis also increases plasma levels of free hemoglobin. Hemoglobin is a potent scavenger of NO and may cause vasoconstriction.² Second, there may be a contribution from endogenous inhibitors of NO synthase. Asymmetric dimethylarginine (ADMA) and N-monomethylarginine . . . [Full Text of this Article]

Jan T. Kielstein, MD
kielstein@yahoo.com

John P. Cooke, MD, PhD
Division of Cardiovascular Medicine
Stanford University School of Medicine
Stanford, Calif

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