Determination of N^G-nitro-l-arginine and N^G-nitro-l-arginine methyl ester in plasma by high-performance liquid chromatography

An HPLC method has been developed for the measurement of the nitric oxide synthase inhibitors, N^G-nitro-l-arginine (l-NOLA) and N^G-nitro-l-arginine methyl ester (l-NAME), in sheep plasma. Using an ion-exchange HPLC column (JWAS 150, 100 × 3.9 mm I.D., Millipore-Waters, Australia) and post-column ninhydrin detection, l-NOLA was separated from valine and other plasma amino acids. When added to sheep plasma, good recovery (mean 102%) and precision (mean coefficient of variation 2.7%) in the measurement of l-NOLA was obtained over the range 2-50 mg/l. l-NAME was unstable in sheep plasma at 37°C, and was converted to l-NOLA with a half-life of 250 min. This method will permit pharmacokinetic parameters to be determined for these potential drugs, and will allow plasma drug concentrations to be correlated with the pharmacodynamic effects of these compounds.