Late-preconditioning protection is evident in the microcirculation of denervated skeletal muscle

We investigated whether ischemic preconditioning induces microvascular prot ection in skeletal muscle at the late phase (after 24 hours) when the same muscles are subjected to prolonged warm global ischemia. The cremaster musc le of the male Sprague-Dawley rat underwent vascular isolation and was subj ected to 4 hours of ischemia and 60 minutes of reperfusion. Early precondit ioning consisted of 45 minutes of ischemia followed by 15 minutes of reperf usion before prolonged ischemia/reperfusion; late preconditioning also cons isted of 45 minutes of ischemia but was done 24 hours (24-hour period of re perfusion) before the prolonged ischemia/reperfusion. Arteriole diameters a nd capillary perfusion were measured with use of intravital microscopy. Fou r groups were compared: rats that underwent early preconditioning, their co ntrols, rats that underwent late preconditioning, and their controls. Early and late preconditioning significantly attenuated vasospasm and capillary no-reflow compared with the controls for each. Average arteriole diameter w as significantly larger in the rats that underwent late preconditioning tha n in any other rats; it was also significantly larger in the controls for l ate preconditioning than in those for early preconditioning. We introduce a model of the rat cremaster muscle that has been isolated from its vascular supply as a useful preparation to study the effects of late preconditionin g on microcirculation in skeletal muscle. Late preconditioning provided bet ter microvascular protection than did early preconditioning. The mechanism for this preconditioning protection is being investigated because it should provide a means for therapeutic intervention.