Evaluation of the interaction between myogenic response and endothelium-derived factor by a microvessel perfusion system

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1. Isolated canine femoral artery : An NO microelectrode (100 μm in diameter) was inserted into the vascular media where flow-induced endothelium-derived NO production was measured NO production was changed with a time constant of about 24 sec, and a linear relation was observed between perfusion rate and produced NO.Flow-induced NO production was attenuated by exogenous NO (SNAP), and this suppressive effect was disappeared by perfusing BH_4, a cofactor of NO synthase (NOS). Simultaneous perfusion of SNAP and Tiron, superoxide scavenger did not affect endogenous NO production. Collectively, exogenous NO perfusion induces a decrease in intracellular BH_4 level, leading to superoxide release from NOS.Reaction between NO and superoxide is known to produce peroxynitrite, which attenuates NOS activity.2. Isolated rat mesenteric small artery : Intravascular-wall NO was visualized by an NO fluorescent indicator (DAF-2DA), and uniformly distributed NO fluorescence was observed during nitroglycerin (NTG) perfusion. In addition, it was found that thiol-containing molecules are involved in the NTG-derived NO production mechanism.3. Isolated perfused rat heart : When perfusion pressure was decreased from 100 to 50 cmH_2O, coronary perfusion rate decreased by half ; however, NO production was nearly doubled Despite decreased coronary perfusion rate by decreased perfusion pressure, NO production was increased in association with regulation mechanism of oxygen supply.4. Estimation method of systemic NO production rate : Plasma nitrate level in blood samples collected after simple 14-hr fasting was measured, and systemic NO production rate was estimated to be about 600 nmol/min by a single-compartment analysis. Compared with other previous estimation methods such as urinary nitrate and RI, estimated values were comparable.