Characteristics of arterial wall shear stress which cause endothelium-dependent vasodilatation in the anaesthetized dog

1. The effects of changes in the mean and amplitude of arterial wall shear stress on endothelium dependent arterial dilatation of the iliac artery of the anaesthetized clog were examined. 2. Changes in the mean and amplitude of blood flow and wall shear stress we re brought about by varying local peripheral resistance and stroke volume u sing a distal infusion of acetylcholine and the stimulation of the left ans a subclavia. Changes in the diameter of a segment of the iliac artery with the endothelium intact, relative to a an index of tile release of nitric ox ide. 3. The increase in mean blood flow was from 84 +/- 12 to 527 +/- 53 ml min( -1) and in amplitude was from 365 +/- 18 to 695 +/- 38 ml min(-1) (means +/ - S.E.M.). The increase in mean wall shear stress was from 1.78 +/- 0.30 to 7.66 +/- 1.01 N m(-2) and in amplitude was from 7.37 +/- 0.46 to 13.9 +/- 2.00 N m(-2) (means +/- S.E.M.). 4. Increases in mean shear stress caused an increase in the diameter only o f the section of artery with endothelium; the slope of the relationship was 0.064 +/- 0.006 mm N-1 m(2) (mean +/- S.E.M., P<0.001); changes in the amp litude of shear stress did not cause an increase in diameter. Changes in bo th the mean anti amplitude of shear stress had no significant effect on the diameter of the section of artery with no endothelium. 5. These findings coupled with the known anti-atheroma effects of nitric ox ide and the effect of shear stress on cell adhesion and platelet aggregatio n offer a possible explanation for the disposition of atheroma in those par ts of the arterial system which have low mean and high amplitude of wall sh ear stress.