Ultrastereologic studies on the myocardial mitochondria in experimental hypothyroidism

Ultrastereologic studies were performed on myocardial mitochondria in experimental hypothyroidism induced by the excision of the thyroid gland. Studies were carried out using accepted methods in stereology according to Weibel et al. Mitochondrial membrane surface areas and relative volumes of individual membranes and compartments were calculated by means of Weibel's grid and square grid. Quantitative studies disclosed that in hypothyrotic animals mitochondrial matrix volume increased, while mitochondrial external compartment volume was reduced, which reflected lowered energy production by mitochondria and its transfer to other subcellular structures of myocardial fibers. The studies allowed to evaluate energy state of mitochondria and enabled to examine the course bioenergetic disturbances within myocardial fibers, the effect of which was progressive heart hypodynamism and failure.