Collaterals are arteriole-to-arteriole anastomoses that connect adjacent arterial trees. They lessen ischemic tissue injury by serving as endogenous bypass vessels when the trunk of one tree becomes narrowed by vascular disease. The number and diameter (“extent”) of native (pre-existing) collaterals, plus their amount of lumen enlargement (growth/remodeling) in occlusive disease, show remarkably wide variation among inbred mouse strains (eg, C57BL/6 and BALB/c), resulting in large differences in tissue injury in models of occlusive disease. Evidence suggests similar large differences exist among healthy humans
