UC San Diego

Vital organ tissue in victims of strokes and heart attacks and patients undergoing cardiac and transplant surgeries present damage resulting from ischemia reperfusion injury in the form of impaired vascular function and tissue perfusion, and inflammatory conditions. Patient studied by diagnostic ultrasound have been found to present significantly attenuated indications of reperfusion injury, leading to the hypothesis that the use of ultrasound could be a therapeutic treatment for ischemia reperfusion injury. These studies were carried out to elucidate the biochemical mechanism underlying ultrasound irradiation's efficacy in the prevention of ischemia reperfusion injury with particular emphasis on the affects on nitric oxide (NO) production. Studies were carried out in the microcirculation using the methods of intravital microscopy and the dorsal skin fold window chamber hamster preparation. In vivo real-time analysis of the microcirculation was performed in the tissue of conscious animal subjects. The principal data assessed was functional capillary density and microvascular diameter, blood flow velocity and flow, in order to assess tissue injury and vessel function. We compare tissue injury with and without ultrasound irradiation as well as ultrasound irradiation during ischemia or reperfusion. We also compare the influence of NO synthase (NOS) inhibition on the effects of ultrasound irradiation of animals. We carried out molecular comparative analysis of irradiated and unexposed tissue by Western Blotting. The effects of ultrasound exposure on inflammatory conditions were determined by assessing venular leukocyte endothelial cell interaction with ultrasound irradiation. Improved microcirculatory function of all vessels following ultrasound irradiation was seen as a long-term effect (24 hours), supporting the hypothesis of injury moderation by diagnostic ultrasound stimulation. Arterioles showed increased flow; capillaries had enhanced perfusion and venules showed decreased leukocyte endothelial cell interaction. Molecular analysis and inhibition of endothelial and inducible NOS clarified the difference between stimulated NO production pathways in causing beneficial effects in the damaged microcirculation. The mechanism underlying the efficacy of ultrasound irradiation in the prevention of ischemia reperfusion injury is evidently mediated by NO production