Mechanism of induction of collateral growth (arteriogenesis). (1) Endothelium senses shear stress via Ca+ channels, transduction via glycocalyx and cytoskeleton. (2) Actin-binding Rho-activating protein (ABRA) and early growth response protein 1 (EDGR1) genes are upregulated. (3) Activated endothelium expresses adhesion molecules such as intercellular adhesion molecule (ICAM) and growth factors such as monocyte chemoattractant protein 1 (MCP1) as well as NO. (4) Circulating monocytes bind their macrophage 1 antigen (Mac-1) receptors to ICAM. (5) Monocytes differentiate into macrophages and secrete additional growth factors and chemoattractants, stimulating proliferation of smooth muscle and endothelial cells. (Illustration by Anne Wadmore, Medical Illustrations Ltd).