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For the study, twenty young rats of Wistar strain, weighing approximately 250gm, were sacrificed. For the experimental group, 8 ㎎ of isoproterenol HCI(1/3’,4’dihydroxyphenyl/2isopropylaminoethanol hydrochloride) per 100gm of body weight was administered for the frequency of two times subcutaneously at intervals of 24 hours, and extraction of the hearts of the experimental animals were performed under ether anesthesia 24 hours after the second injection of isoproterenol. After extraction, the volume of each heart was measured by the Archimedes principle, and the wet weight of that was also measured. Paraffin sections of the heart tissue fixed with 10% neutral fromalin were stained with hematoxylin and eosin for routine study, and those fixed with absolute ethanol with von Kossa staining for histochemical study of calcium ion. Stained section were examined under light microscope. For electron microscopic study, the remainder part of the heart tissue was cut into one mm^3 in size, and was fixed with 2% glutaraldehyde in 0.2M phosphate buffer, pH7.4 and post-fixed with 1% osmium tetroxide in 0.2M phosphate buffer, pH7.4. After dehydration with ascending alcohols from 70% and resin infiltration, each tissue specimen was embedded into epon 812. Ultrathin sections were stianed with 4% uranyl acetate and lead citrate and were examined under JEOL200-CX transmission electron microscope. The results obtained were as follows: 1. There was a significant increase in the weight of heart of the experimental group. 2. The major site of injury was the left ventricle, especially the apex of the experimental group. 3. In the experimental group, there was widespread inflammatory cell infiltration, swelling of myocardial fibers and focal wavy appearance of them in the myocardium of the left ventricle including apex. 4. In the experimental group, there was widespread calcium ion deposit in the myocardium. 5. By electron microscopic study, there was loss glycogen granules, mitochondrial swelling, destruction of mitochondrial cristae, and infiltration of macrophages at the margin of inflummed area of myocardium of affected area.
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