Fine Structure of Cardiac Muscle Cells after Injection of Normal and Thiouracil-Treated Rats with Triiodothyronine.

Abstract

It has been reported that morphologic changes occur in mitochondria of cardiac muscle cells following treatment with thyroid hormones (thyroxine, triiodothyronine). These observations have been used to support the view that under normal conditions, thyroid hormones control mitochondrial metabolism. We have examined the effect of triiodothyronine on the fine structure of cardiac muscle from normal and thiouracil-treated rats. Rats were given thiouracil (0.1 percent in drinking water) for 10 weeks. Normal and thiouracil-treated rats were injected with triiodothyronine (75 ug of triiodo-L-thyronine i.p. per day) for three days. The left ventricular muscle of normal rats, and rats given thiouracil, triiodothyronine or thiouracil followed by triiodothyronine was examined ultrastructurally. Morphometric analysis of electron micrographs showed that mitochondrial number was not significantly different in the four groups of animals. The fine structure of normal cardiac muscle is illustrated in figure 1. Thiouracil treatment did not alter the fine structure of cardiac muscle cells (Fig. 3).