Muscle mitochondrial ultrastructure in exercise-trained iron-deficient rats.

To investigate effects of endurance training and iron deficiency, as well as the combination of these two conditions, on mitochondrial ultrastructure, weanling rats at 3 wk of age were assigned to iron-deficient (Fe-) and iron-sufficient (Fe+) groups. Subsequently, groups were subdivided into exercise-trained (T) and sedentary (S) groups. Electron microscopy showed subsarcolemmal and intrafibrillar mitochondria in the Fe-T animals to be enlarged with sparse cristae and vacuole-like areas compared with the other groups. An increase in the number of lipid droplets in both Fe- groups was observed. Stereological measurements revealed a 99% increase in the volume occupied by muscle mitochondria in the Fe-T animals (11.9 +/- 0.8%) over the Fe+T (5.9 +/- 0.4%) and Fe+S (6.0 +/- 0.3%) groups and a 55% increase over the Fe-S groups (7.7 +/- 0.3%). The ratio of mitochondrial surface area to tissue volume was significantly decreased only in the Fe-T group. These results indicate that the combined stresses of iron deficiency and training produce mitochondrial ultrastructural changes far greater than those of iron deficiency or training alone. Because this is also the case with the disproportion among mitochondrial enzymes, it is possible that the ultrastructural changes are indicative of morphological responses that maintain ATP turnover during exercise in iron deficiency when oxygen transport and electron transport chain activities are reduced.