Studies on the cardiomegaly of the spontaneously hypertensive rat.

Changes in size, morphology, and certain relevant biochemical components of hearts from spontaneously hypertensive and normal Wistar rats were studied comparatively. Groups of rats were killed at stages which represented developing and stable cardiac hypertrophy and approaching cardiac failure. Mitochondrial content was determined by comparing cytochrome oxidase activity per milligram of heart homogenate protein with cytochrome oxidase activity per milligram of heart mitochondrial protein. Based on the relationship of heart weight and body weight found in normotensive rats (hearts weight [mg] = 1.85 x body weight [g] + 287), left ventricular dimensions, and micrographs of left ventricular muscle fibers, hypertrophy of the hearts from the spontaneously hypertensive rats was conclusively demonstrated. Approximately 25% of the total heart protein was mitochondrial in both control and hypertensive rats; the percent increased during the period of rapid growth but subsequently decreased with age. The amount of heart mitochondrial protein was greater for spontaneously hypertensive rats relative to body weight but was not greater relative to heart weight. The maximum increase in heart mitochondria relative to body weight was observed in 6-month-old spontaneously hypertensive rats, whereas the maximum increase in heart weight occurred at 12 months of age. A decrease in heart weight occurred in 17-month-old spontaneously hypertensive rats. No preferential retention of mitochondria was apparent during atrophy induced by starvation in either control or hypertensive rats.