Effects of thyroid hormones in vitro on tissue respiration, oxidative phosphorylation and the swelling of mitochondria

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Abstract
The action of thyroid hormones (L-thyroxine, tetraiodothyroacetic acid and triiodothyroacetic acid) was compared with that of stilbestrol upon selected enzymic activities. The increased respiration of kidney slices of thyroidectomized rats, reported for the thyroacetic acids by Thibault and Pitt-Rivers (1955a, b), was not confirmed. The inhibitory effect upon oxidative phosphorylation in rat-liver mitochondrial preparations shown by thyroxine is more pronounced with the 2 acetic acid analogues. Whereas preliminary contact with thyroxine is necessary, the thyroacetic acids cause immediate uncoupling of respiration and phosphorylation, similar to that previously found for stilbestrol. The adenosine triphosphatase activity of myosin is powerfully inhibited by all 3 thyroid hormones. The swelling of rat-liver mitochondria, which is increased by thyroxine, is found to be even greater with the thyroacetic acids. p-Chloromercuri-benzoate at higher concentrations also causes the swelling of mitochondria. Stilbestrol stabilizes the state of swelling of the mitochondria and neutralizes the swelling action of the thyroacetic acids.