l-Arginine is an important precursor of nitric oxide (NO) and protein synthesis. Arginine is produced in the body (mainly kidney) by de novo production from citrulline and by protein breakdown. Arginine availability appears to be limited in sepsis.
Objective
The objective was to compare arginine and citrulline metabolism in septic patients and nonseptic control patients in an intensive care unit (ICU) and in healthy control subjects.
Design
Ten patients with septic shock, 7 critically ill control patients, and 16 healthy elderly subjects were studied. Metabolism was measured by using a primed continuous (2 h) stable-isotope infusion protocol. NO production was calculated as the conversion rate of arginine to citrulline; de novo arginine production was calculated as the conversion rate of citrulline to arginine. Arterial blood (arterialized venous blood in healthy subjects) was collected for the measurement of amino acid enrichment and concentrations. Data are reported as means ± SDs.
Results
Whole-body citrulline production was significantly lower in septic patients (4.5 ± 2.1 μmol · kg−1 · h−1) than in ICU control patients (10.1 ± 2.9 μmol · kg−1 · h−1; P < 0.01) and in healthy control subjects (13.7 ± 4.1 μmol · kg−1 · h−1; P < 0.001). Accordingly, de novo arginine production was lower in patients with sepsis (3.3 ± 3.7 μmol · kg−1 · h−1) than in healthy controls (11.9 ± 6.6 μmol · kg−1 · h−1; P < 0.01) and tended to be lower in septic patients than in ICU control patients (10.9 ± 9.4 μmol · kg−1 · h−1; P = 0.05). NO production was lower in septic patients than in healthy control subjects (P < 0.01), whereas a larger part of arginine was converted to urea in sepsis.
Conclusions
Citrulline production is severely low in patients with sepsis and is related to diminished de novo arginine and NO production. These metabolic alterations contribute to reduced citrulline and arginine availability, and these findings warrant further studies of therapeutic nutritional interventions to restore arginine metabolism in sepsis.
