Endothelin-1 and the aortic valve.

The aortic valve is a complex structure, the function of which is fundamental to sustain life. Previously believed to be an inert structure that merely opens in response to the forward flow of blood out of the left ventricle, it is now established that it is a sophisticated structure with specific biological properties. However, little is known about the mechanisms that regulate its function. In this respect, endothelin is of particular interest due to its range of biological actions within the cardiovascular system that suggest it may be capable of stimulating the cells that reside in valve cusps. Endothelin can be detected in the endothelial cells that cover valve cusps and it has been demonstrated that it is has the ability to stimulate contractile responses of cusp tissue in vitro. These contractions vary with different regions of the aortic valve cusp and occur preferentially in the circumferential direction. In addition, evidence exists that suggests endothelin may also have a role in the morphogenesis of the aortic valve. Further studies are required to determine the significance of the effects mediated by endothelin on cusp tissue to the function of the aortic valve in health and disease.