Isoproterenol induced rat endomyocardial damage in relationship to local capillary geometry

Isoproterenol (2 mg/kg) injected subcutaneously into male Sprague-Dawley rats elicited morphological damage in the endomyocardium which was analyzed 16 h following injection. Our aim was to study the relationship between damaged individual myocytes and their capillary supply. Myocardial tissue sections were differentially stained in order to distinguish arteriolar (AC) and venular (VC) capillary portions. Tissue areas surrounding individual capillaries and the position of the capillaries with respect to the damaged individual myocytes were established by using the method of "capillary domains". In multicellular necrotic lesions 84% of the capillaries located within the necrotic foci and 77% of the capillaries in the surrounding tissue area were identified as the distal, venular portion with presumably low O2 content. The proportion of VCs related to necrotic lesions was significantly higher than in surviving endomyocardial regions. In the case of individual necrotic myocytes, we found 88% to be supplied by VCs, while the adjacent normal myocytes were supplied by 61% VCs. Both values were significantly higher when compared to control hearts (42%). These results strongly support the crucial role of a lack of oxygen delivery in the pathogenesis of isoproterenol-induced necrosis.