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.
KEY WORDS cytochrome oxidase deoxyribonucleic acidcardiac hypertrophy heart mitochondria hypertension B Hypertension, accompanied by an enlargement of the heart, can occasionally be related to cardiovascular, neurogenic, endocrine, or renal lesions. However, in 90% of the cases, the etiology of the hypertension is unknown. In his search for the animal model that would most nearly approximate essential hypertension in man, Okamoto (1) has developed, through inbreeding, a strain of Wistar rats known as spontaneously hypertensive rats. Without exception these rats develop hypertension with age; this hypertension is accompanied by cardiomegaly in stages paralleling its development in man. Advantageously, in this animal model the entire life history of the disease is compressed within a period of less than 2 years. A number of investigators (2-12) have studied in some detail the biochemical changes which occur in induced cardiomegaly. However, the molecular From the Departments of Biochemistry and Surgery, Indiana University School of Medicine, Indianapolis, Indiana 46202, and the Department of Microbiology, University of Guelph, Guelph, Ontario, Canada.ITiis work was supported by U. S. Public Health Service Specialized Center Grant HL-14159 from the National Heart and Lung Institute.Received July 6, 1973. Accepted for publication March 20, 1974. mechanisms and signals responsible for cardiac enlargement in response to an increase in work load remain...
