Flow dependence and time constant of the change in nitric oxide concentration measured in the vascular media

It has been considered that the concentration of endothelium-derived nitric oxide (NO) in the arterial vascular wall changes in response to flow-induced shear stress. In the present study, using an NO-sensitive electrode, the aim was to directly evaluate the relationship between perfusion rate and NO concentration in the arterial vascular wall. The NO microelectrode (diameter: 100 μm) was inserted into the vascular media of isolated canine femoral arteries, and the vessel was perfused with a Krebs-henseleit buffer solution. A flow-related change in NO concentration in the vascular media was then evaluated by changing perfusion rate. NO concentration attained a peak value with a first-order time delay by a stepwise increase in perfusion rate, and the peak-level NO concentration was linearly correlated with perfusion rate in each vessel (10–154 pA at 2.1–72.3 ml min−1; n=7, r2=0.89–0.99, p<0.03). The average time constant for an increase in NO current with a stepwise increase in perfusion rate was 24±3 s (n=5). No production was increased by perfusing a solution containing 1 mmol l−1 L-arginine and was attenuated by 100 μmol l−1 NG-nitro-L-arginine, indicating the intactness of the endothelium, proper insertion of the NO electrode and selective detection of NO by the electrode. It is concluded that the NO microelectrode is applicable to NO measurement in the vascular media where NO controls vascular tone and that the concentration of NO in the arterial vascular media changes with perfusion rate in a rate-dependent manner as well as with a time constant of about 24 s for a stepwise increase in flow.