The subepicardial microcirculation in heterotopically transplanted mouse hearts: an intravital multifluorescence...

We developed a model for intravital microscopic analysis of the coronary microcirculation in transplanted murine hearts and assessed the influence of cold ischemia on postischemic microcirculatory dysfunctions.

Murine hearts were exposed to 60 (n = 12) and 240 minutes (n = 8) of cold ischemia before syngeneic heterotopic transplantation. Intravital fluorescence microscopy allowed detailed analysis of the right ventricular coronary microcirculation, including feeding arterioles, nutritive capillaries, and postcapillary venules. With this technique, we further studied leukocyte-endothelial cell interactions, microvascular permeability, tissue oxygenation, and microlymphatics.

Cold ischemia of 240 minutes aggravated nutritive capillary perfusion failure, indicated by a significant reduction of functional capillary density and capillary flow velocity by 63% and 45% (P < .05 vs 60-minute cold ischemic isografts). The mitochondrial redox state, visualized by nicotinamide adenine dinucleotide hydrogen autofluorescence, was markedly deteriorated after 240-minute cold ischemia (P < .05), indicating a persistent mismatch between oxygen supply and demand resulting from pronounced capillary no-reflow. Prolonged ischemia further resulted in 6- and 11-fold higher numbers of rolling and firmly adherent leukocytes in postcapillary venules (P < .05), together with increased microvascular permeability.

We introduce a novel approach to visualize in detail the murine coronary microcirculation in vivo by multifluorescence microscopy. Our data demonstrate that prolonged cold ischemia provokes posttransplant capillary no-reflow, leukocytic inflammation, and persistent tissue hypoxia.