Measurement of NO synthesis in humans by L-[N-15(2)]arginine: Application to the response to vaccination

Induction of nitric oxide (NO) synthesis is a key element of the inflammatory response in humans. We describe a sensitive gas isotope ratio mass spectrometric (GIRMS) method for measuring urinary [N-15]nitrate production during intravenous infusion of L-[guanidino-N-15(2)]arginine and its application to investigate the effects of a controlled inflammatory stimulus, typhoid vaccination, on NO synthesis in humans. Intravenous infusion of L-[N-15(2)]arginine at 5-12 mu mol . kg(-1) . h(-1) for 24 h in three subjects was used to determine arginine and nitrate pool kinetics. Eight subjects received primed constant infusion of 2.5 mu mol . kg(-1) . h(-1) of L-[N-15(2)]arginine for 12 h once before and again after typhoid vaccination. NO synthesis was calculated from N-15 enrichment of plasma arginine and urinary nitrate, measured by gas chromotography mass spetrometry and GIRMS, respectively and total urinary nitrate excretion. Baseline NO synthesis was 298 +/- 44 nmol . h(-1) . kg lean body mass(-1), representing 0.41% of arginine flux. After vaccination, NO synthesis (267 +/- 77 nmol . h(-1) . kg(-1)) was not increased (P = 0.18), despite demonstration of an acute phase response. Typhoid vaccination is not accompanied by accelerated NO synthesis.