L-arginine (L-arg) is a semi-essential amino acid, which is the substrate for both nitric oxide synthase (NOS) and arginase. NOS converts L-arg to NO and L-citrulline (L-cit) while arginase converts L-arg to urea and L-orn, the L-orn can then be converted to L-cit via ornithine transcarbomylase. In pediatric patients the plasma concentration of L-arg (40-150 μM) should be nearly saturating for NOS and arginase. Therefore, we asked the question, would the infusion of L-arg result in increased L-arg metabolism in pediatric patients. We studied 11 pediatric patients scheduled for L-arg challenge tests by the endocrinologists. The children were given 500 mg/kg L-arg intravenously as a 30 minute infusion. Blood pressure was monitored, and plasma samples were obtained at 0, 30 and 90 minutes (time 0 is the start of the L-arg infusion) for determination of nitrite/nitrate (NOx), L-arg and L-cit. The results are shown in the Table as mean (SE), MAP is mean arterial blood pressure (mmHg), the L-arg, NOx and L-cit are μM, * signifies different from time 0, p<0.05, + different from time 30, p<0.05. The L-arg infusion caused a small but significant decrease in MAP. The L-cit results demonstrate that administration of exogenous L-arg increased L-arg metabolism in pediatric patients. These results may have implications in the treatment of disorders characterized by decreased L-arg metabolism.

Table 1 No caption available.
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