Stimulation of chick liver mitochondrial protein synthesis by thyroxine without mitochondrial swelling.

Abstract

Thyroxine (T4) is known to stimulate rat liver mitochondrial protein synthesis and increase mitochondrial volume (so-called “swelling”) in vitro. It has been suggested that this effect of T4 on mitochondrial structure is required for the effect on protein synthesis. However, this report on the effect of T4 on chick liver mitochondria shows that 20 µM and 50 µM T4 increased protein synthesis 37 ± 3% and 65 ± 6%, respectively, in the absence of swelling. On the other hand, T4, which increases O2 consumption by rat liver mitochondria in vitro, did not increase Oo consumption by chick liver mitochondria. Therefore, swelling is associated with a catabolic effect (increased O2 consumption) of T4 but not with an anabolic effect (increased protein synthesis). (Endocrinology 94: 871, 1974)