Figure 2.

Schematic diagram illustrating the balance hypothesis of the angiogenic switch. It is speculated that an angiogenesis switch mechanism tightly regulates normal angiogenesis (formation of new capillaries). This balance can be disrupted to favor increased blood vessel formation through inducers and inhibitors of angiogenesis, which activates the switch. Reducing the inhibitor concentration, e.g., thrombospondin-1, 16kD prolactin, Interferon αιβ, Platelet factor-4, Angiostatin, etc. or increasing the activator levels, e.g., aFGF, bFGF, VEGF, etc., can change the balance and activate the switch, which could lead to the growth of new blood vessels. ¹³