Nitric oxide and muscle V̇O2 kinetics

In a recent report in The Journal of Physiology, Grassi et al. (2005) examined the influence of nitric oxide synthase (NOS) inhibition with Nω-nitro-l-arginine methyl ester (l-NAME) on muscle oxygen uptake (VO2) kinetics in the pump-perfused canine hind-limb model, and concluded that ‘the inhibition of mitochondrial respiration by nitric oxide (NO) does not limit the kinetics of adjustment of oxidative metabolism at exercise onset’. This conclusion contradicts the results of previous studies which have demonstrated a significant speeding of VO2 kinetics with l-NAME administration in horses and humans (Kindig et al. 2001, 2002; Jones et al. 2003, 2004; Wilkerson et al. 2004). We contend that limitations inherent in the experimental model utilized by Grassi et al. (2005) might at least partly explain the differences in the results obtained.

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