The role of EDRF in flow distribution: a microangiographic study of the rabbit isolated ear.

A microangiographic technique was used to study the influence of endothelium-derived relaxing factor (EDRF) on vasomotor control mechanisms in resistance vessels of intact buffer-perfused rabbit ear. Selective inhibition of EDRF activity by hemoglobin unmasked an intrinsic ("myogenic") constrictor response to sudden increases in flow rate. EDRF activity was greatest in arteries in which calculated shear stress and hydraulic resistance were maximal, namely the central ear artery and its first generation of branch arteries: these are proximal "feed" vessels (150-700 microns internal diameter) in this bed. The findings are consistent with enhancement of EDRF release by the physical stimulus of shear stress in resistance vessels as previously demonstrated in conduit vessels-a phenomenon which is likely to exert a major influence on flow in vascular networks. EDRF activity thus reduced perfusion pressure and power losses, particularly in highly constricted preparations. Shear-induced release of EDRF may provide an integrating link between flow and arterial topography by optimizing perfusion characteristics over a wide range of flow rates.