Cellular mechanisms of acute versus delayed preconditioning

Ischemic preconditioning (IPC) refers to the phenomenon by which the deleterious effects of prolonged ischemia followed by reperfusion (I/R) are ameliorated by prior exposure to a brief (and non-damaging) period(s) of vascular occlusion. Typically, the protection is seen within minutes of the initial I/R challenge and disappears within hours. Delayed preconditioning refers to a similar, yet distinct, phenomenon which is characterized by the delayed onset of the protective effects following a period of preconditioning ischemia. This second window of protection becomes effective 24 h or later after exposure to preconditioning ischemia. The characteristics and mechanisms involved in both PC and delayed PC are addressed and a unifying theme which links both phenomenon will be presented.