Stereospecific pharmacodynamics and chiral inversion of NG‐nitro‐arginine in the beagle dogs

In the present study, we analyzed the stereospecific pharmacodynamics and inversion of NG-nitro-arginine by an intravenous blous injection of L-NG-nitro-arginine (L-NNA) or D-NG-nitro-arginine (D-NNA) (10 mg/kg) in beagle dogs. Significant pressor responses were observed for both substances, though a similar maximum response induced by L-NNA was reached at 120 min slower as compared with D-NNA. The rise in mean arterial pressure (MAP) of D-NNA dogs was also shown to be slower than the L-NNA group. Our data showed that D-NNA had no impact on MAP within 60 min after its injection. Plasma L-NNA started to appear after 45 min posterior to the i.v. bolus injection of D-NNA. This chiral inversion is unidirectional because no D-NNA was not produced from L-NNA. The pressor response in the D-NNA-injected dogs was well parallel to the plasma L-NNA concentration. Similar disposition of NG-nitro-arginine enantiomers and 4% of chiral inversion ratio from D-NNA to L-NNA was found in the beagle dogs. Given that D-amino acid oxidase (DAAO) is the essential enzyme in chiral inversion of D-NNA, we further compared the enzymatic activity of the renal DAAO between dogs and rats. Our data showed that dogs had a significantly lower enzymatic activity than rats, thus supported a lower inversion ratio of D-NNA in dogs. Chirality, 2010. © 2010 Wiley-Liss, Inc.