Quantitative morphometric determination of arteriolar and capillary perfusion within ischemic rabbit left ventricle

The aim of this study was to identify the percentage of the capillary and arteriolar beds that was perfused at a given time or that was capable of being perfused within subepicardium and subendocardium of ischemic and nonischemic myocardium of anesthetized, open-chest rabbits. Fluorescein isothiocyanate-dextran (150,000 MW) was injected intravenously to label perfused microvessels of rabbits that were subjected to 60 min of coronary artery occlusion. Fluorescent microscopy was used to identify the perfused vessels and an alkaline phosphatase stain was employed to locate the total microvasculature. Stereological principles were utilized to determine various morphometric parameters. After 14 sec of dextran injection, approximately 66 +/- 2% (mean +/- SEM) of the capillaries and 65 +/- 5% of the arterioles (19-50 microns) were perfused within ischemic myocardium. Two minutes after dextran injection, 72 +/- 3% of the capillaries and 94 +/- 4% of the arterioles were perfused within the ischemic myocardium. In the nonischemic myocardium, 64 +/- 2% of the capillaries and 59 +/- 5% of the arterioles were perfused 14 sec after dextran injection, while 94 +/- 1% and 96 +/- 2% of the capillaries and arterioles, respectively, were perfused 2 min after dextran injection. It is concluded that a significant unperfused reserve of arterioles exists, but a significant portion of the capillary bed is incapable of being perfused within ischemic rabbit myocardium.