Mechanisms of vasoconstriction.

The contractility of vascular smooth muscle cells is controlled in a complex manner by both extracellular and intracellular messages. The vascular endothelium does not simply act as a physical barrier between the blood and smooth muscle cells, it integrates intravascular signals and controls the contractility of underlying smooth muscle cells by way of release of paracrine factors with contracting or relaxing properties. Vasoconstrictors trigger a cascade of interacting intracellular signals that concur in initiating and maintaining contractions. Each step of these signalling pathways is a possible logical site for potential therapeutic interventions.