Alterations of Mitochondrial Structure Induced by Thyroid Hormonesin Vivoandin Vitro

Abstract

Mitochondria was isolated from livers of normal rats and rats made thyrotoxic by daily injection of 1 [mu]g/g body weight of 3,5,3[image]-trilodo-L-thyronine for 9 days. These mitochondria were incubated at 37 C[degree] for 1 hr. In addition, mitochondria isolated from normal rats were incubated in the presence of 5 x 10-5 [image] L-thyroxine. Samples taken from the incubation mixtures at various times were examined by electronmicroscopy. It was shown that control mitochondria incubated without hormone present undergo structural changes before they lose matrix material. These changes consist of some corrugation of outer membranes, and a clumping of the intra-mitochondrial granules. Later, after about 20 min. of incubation, matrix is lost from the mitochondria, and the mitochondrial membranes become diffuse in appearance. Thyroid hormones, given in vivo or added in vitro, eliminate the clumping of intramitochondrial granules, accelerate the loss of matrix, and improve the appearance of mitochondrial membranes as they are seen late in the incubation, although this last effect is not very striking in the case of hormone added in vitro. These results are discussed in light of earlier biochemical results of the same experiments and of the known effects of thyroid hormones on mitochondrial metabolism.