Bayliss Effect

The Bayliss effect (or Bayliss myogenic response) was discovered by physiologist Sir William Bayliss in 1902. It has subsequently been found, that denudation of the prepared vessels consistently changed the response of the vascular vessels, and these studies resulted in the conclusion, that the endothelial cell layer and the muscle cells are involved in the effect. When blood pressure is increased in an artery (this has a tendency to distend it), a common response is a sustained contraction within the artery as a form of autoregulation. This helps to maintain local blood flow, as the increase in vasoconstriction of the artery will lead to an increase in total peripheral resistance (TPR) and thus reduce flow. Conversely, if there is a drop in blood pressure there is usually a reduction in the amount of constriction of the affected artery to help maintain flow, but a balance of vascular constriction and distension is usually maintained as an autoregulatory process.

Proposed mechanism

When the endothelial cell in the tunica intima of an artery is stretched it is likely that the endothelial cell may signal constriction to the muscle cell layer in a paracrine fashion. Increase in blood pressure may cause depolarisation of the affected myocytes as well or endothelial cells alone. The mechanism is not yet completely understood, but studies have shown that volume regulated chloride channels and stretch sensitive non-selective cation channels lead to an increased probability in opening of L-type (voltage-dependent) Ca²⁺ channels, thus raising the cytosolic concentration of Ca²⁺ leading to a contraction of the myocyte, and this may involve other channels in the endothelia.

References

* J. R. Levick. "An introduction to cardiac physiology." ISBN: 0340763760.