Acute administration of 3,5-diiodo-L-thyronine to hypothyroid rats affects bioenergetic parameters in rat skeletal muscle mitochondria.

We investigated the mechanism by which 3,5-diiodo-l-thyronine (T2) affects skeletal muscle mitochondrial bioenergetic parameters following its acute administration to hypothyroid rats. One hour after injection, T2 increased both coupled and uncoupled respiration rates by +27% and +42%, respectively. Top-down elasticity analysis revealed that these effects were the result of increases in the substrate oxidation and mitochondrial uncoupling. Discriminating between proton-leak and redox-slip processes, we identified an increased mitochondrial proton conductance as the "pathway" underlying the effect of T2 on mitochondrial uncoupling. As a whole, these results may provide a mechanism by which T2 rapidly affects energy metabolism in hypothyroid rats.