Increase in number and decrease in size of mitochondrial profiles in myocytes of the right ventricle of dogs with...

An ultrastructural study of the myocardium in control dogs and in dogs with papain-induced emphysema of 6 months duration without signs of right ventricular hypertrophy was undertaken to determine the number, size, and relative volume of the mitochondria. In the right ventricle of the emphysematous dogs, the number of mitochondrial profiles was greater per unit area of tissue (46.18 +/- 1.28/100 micron 2 versus 41.20 +/- 1.60/100 micron 2, p less than 0.05), but the mitochondria were smaller in size (mean mitochondrial profile area: 0.39 +/- 0.01 micron 2 versus 0.46 +/- 0.02 micron 2, p less than 0.05; mean mitochondrial "diameter": 0.65 +/- 0.01 micron versus 0.71 +/- 0.02 micron, p less than 0.05) than in control dogs. A highly significant negative correlation was found in the right ventricle of control and emphysematous dogs between the number per unit area and the size (area) of the mitochondrial profiles (r = -0.92; p less than 0.001). The increase in number but decrease in size of the mitochondrial profiles resulted in an unchanged relative volume of mitochondria in the right ventricle of the emphysematous dogs. In the subendocardium and in the subepicardium of the left ventricle of the papain-treated dogs, these changes were smaller and did not reach significance. These ultrastructural changes in the myocardium of the emphysematous animals are considered to be a response to a situation of prolonged increase in work of the right ventricle and may represent an early stage of a developing right ventricular hypertrophy.