MICROCIRCULATORY PROTECTION IN LATE PRECONDITIONING

University Of Nevada Reno, Reno NV

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Abstract

DESCRIPTION (adapted from the applicant's abstract) Ischemia and reperfusion in skeletal muscle is unavoidable during many vascular and musculoskeletal reconstructive surgeries. It can result in microvascular damage leading to significant postoperative complications including muscle dysfunction and necrosis. Recent literature indicates that short periods of ischemia trigger an adaptive response in both an early phase (2 hours after the initial short ischemia) and in a late phase (24 hours after the initial short ischemia) which protect the muscle against injury from a subsequent prolonged period of ischemia and reperfusion. This phenomenon is called "ischemic preconditioning" (IP). If used with reconstructive surgery, IP could prevent many of the post-surgical complications. The investigators' previous experiments demonstrate that microcirculatory protection induced by IP in skeletal muscle is even greater in the late phase than in the early phase. However, the microvascular mechanisms of IP have not been determined. Very little work has been done in the skeletal muscle microcirculation to identify these mechanisms, especially for the late phase of protection. Based on the literature and their previous findings, they hypothesize that IP-induced microvascular protection in the late phase is mediated through an adenosine or nitric oxide initiated, PKC and inducible nitric oxide-dependent pathway. The investigators have developed a vascular isolated rat cremaster muscle preparation with local intra-arterial drug infusion as a model to study microcirculation responses in vivo in late phase IP and to elucidate the mechanisms underlying this microvascular protective action. The experimental procedure consists of 45 mins of ischemia (IP) followed by 24 hrs of reperfusion. There is then 4 hrs of prolonged ischemia followed by 1 hr of reperfusion. Arteriole diameters and capillary perfusion will be measured utilizing intravital microscopy. Acetylcholine and nitroprusside will be infused into the vascular network of the cremaster muscle to test the endothelium dependent nitric oxide system. Finally, the cremaster will be processed for Nitroblue Tetrazolium Staining measurement of cremaster muscle necrosis. The first series of experiments are designed to determine whether adenosine or nitric oxide is the trigger for and can independently induce microvascular protection in the late phase of IP. The second series will establish if microcirculatory protection in the late phase of IP involves activation of PKC and if exogenous adenosine or nitric oxide can provide that activation. The third series of experiments will determine if microvascular protection induced by adenosine, nitric oxide, protein kinase C activation, or by IP, is dependent on the activation of iNOS.