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Cardiac Hypertrophy in Rats with Iron and Copper Deficiency: Quantitative Contribution of Mitochondrial Enlargement

ExtractQuantitative studies of the ultrastructure of heart muscle in iron- and copper-depleted rats show an increased mitochondrial area that contributes to cardiac hypertrophy in both conditions. The mean ratios of mitochondrial/myofibrillar areas are 1.73 and 1.69, respectively, in the deficient groups compared with 0.70 in control animals. The markedly enlarged mitochondria appear to displace and distort the myofibrils. After iron-deficient rats are provided with iron, the reversal of the abnormal mitochondrial/myofibrillar ratio and of cardiac hypertrophy requires about 16 days or approximately twice as long as the complete repair of anemia.In heart muscle from iron-deficient animals, the mitochondrial cytochromes, which all contain iron, remain essentially normal in concentration. In the copper-deficient rats, in contrast, cytochrome a+a3, which contains copper, is depressed to less than one-half the normal concentration. Isolated mitochondria from heart and liver of all animals deficient in iron and copper function normally with respect to respiration and phosphorylation. Thus, a correlation between abnormality of mitochondrial structure, composition, and function is not as yet apparent.The mitochondrial contribution to the cardiac hypertrophy of iron and copper deficiency cannot be attributed entirely to increased work load secondary to anemia, particularly in copper-deficient rats whose cardiac enlargement precedes the development of anemia. The morphologic changes are distinct from those observed in experimental work hypertrophy and can represent a response to the lack of essential precursors required for the cytochromes or other mitochondrial constituents.Speculation: Cardiac hypertrophy in iron and copper deficiency is in part attributable to enlargement of the mitochondrial compartment. This results from the lack of trace metals required for the production of cytochromes or other mitochondrial constituents.