[The regulation of the lumen of the major arteries in accordance with the shear stress on the endothelium].

A decrease in the blood viscosity due to hemoconcentration, caused arterial dilatation. These viscosity-induced responses depended on intact endothelium. The dilatory responses caused by equal increments in flow rate, increased in systemic hemoconcentration and decreased in systemic hemodilution. The data obtained corroborate the suggestion that stress applied to endothelium is the key signal in the control of arterial lumen by the blood flow rate.