Exercise Capacity and Quality of Life in Patients With Idiopathic Pulmonary Hypertension and Eisenmenger Syndrome Receiving Short Term Oral L-Citrulline Malate

Pulmonary vascular tone is maintained by the action of vasoprotective compounds including nitric oxide (NO)(1).NO can be synthesized endogenously in the body via L-arginine and NOS-independent mechanism from the anion nitrite (NO2-)(2,3).Nitric oxide (NO) causes cyclic guanosine monophosphate-mediated vasodilatation of the pulmonary vasculature. Endogenous NO is also produced from the metabolism of citrulline; an amino acid generated by the urea cycle (4). NO is critical for normal development of the pulmonary vasculature and loss of this vasodilator factor and subsequent endothelial dysfunction is proposed as one of the possible explanations for development of pulmonary hypertension (1).

From a clinical standpoint, pulmonary hypertension is a common complication of chronic obstructive pulmonary disease (COPD).Its presence is associated with shorter survival and worse clinical outcome. In a setting of COPD, pulmonary hypertension tends to be of moderate severity and progresses slowly. Recent investigations have demonstrated endothelial dysfunction and changes in the expression of endothelial-derived mediators that regulate vascular tone and cell growth in the pulmonary arteries of patients with mild disease(5). Pulmonary vascular involvement from congenital heart disease like Eisenmeger syndrome is another important category of patients with PAH. In this congenital disease pulmonary vascular involvement follows a period in which pulmonary resistance is low and pulmonary blood flow is high (6, 7, 8). Finally, Idiopathic pulmonary hypertension (IPAH) is the third category of these patients. IPAH has unknown etiology and is characterized by progressive obliteration of small and medium size pulmonary arteries; elevation in pulmonary arterial pressure, and an increase in pulmonary vascular resistance. Presence of these pathologies eventually leads to right heart failure and death (9).