Pharmacokinetic-pharmacodynamic profile of systemic nitric oxide-synthase inhibition with L-NMMA in humans.

aimsIt has been demonstrated that inhibition of endothelium derived nitric oxide with NG-monomethyl-L-arginine (L-NMMA) results in a different cardiac and peripheral vascular response. The purpose of this study was to investigate the pharmacokinetic-pharmacodynamic profile of L-NMMA and pharmacokinetic interactions with L-arginine in healthy subjects.

methodsPlasma pharmacokinetics were analysed from two different studies: In study 1, 3 mg kg-1 L-NMMA was administered i.v. over 5 min and systemic haemodynamics, cardiac output (CO), fundus pulsation amplitude (FPA), and NO-exhalation (exhNO) were measured at baseline and 15, 65, 95, 155, and 305 min after start of drug administration (n=7). In study 2, 17 mg kg-1 min-1 of the physiologic substrate for nitric oxide synthase, L-arginine, was coinfused i.v. over 30 min with a primed constant infusion of 50 microg kg-1 min-1 L-NMMA (n=8).

resultsBolus infusion of L-NMMA resulted in a maximum plasma concentration of 12. 9+/-3.4 microg ml-1 (mean+/-s.d.) with elimination half-life of 63. 5+/-14.5 min and clearance of 12.2+/-3.5 ml min-1 kg-1 and caused a small hypertensive response, decreased CO by 13%, FPA by 26%, exhNO by 46% and increased systemic vascular resistance by 16% (P<0.05 each) 15 min after start of drug administration. Although only limited data points were available in the L-NMMA plasma concentration range between 0 and 4 microg ml-1, drug effects over time were in good agreement with an Emax model (r2>0.98 each), which also suggested that concentrations producing half-maximum effects were higher for FPA than for CO and exhNO. The coinfusion with L-arginine caused a nearly two-fold increase in plasma L-NMMA levels, indicating a pharmacokinetic interaction.

conclusionsIn the absence of a systemic hypertensive response, L-NMMA significantly decreased CO, exhNO, and FPA. The concentration calculated to produce a half maximal effect was equivalent for exhNO and CO, but markedly higher for FPA. Furthermore, measurement of FPA is susceptible to changes in L-NMMA levels at small plasma concentrations.