Effects of triiodothyronine on oxidative phosphorylation in immature rat brain mitochondria

Oxidative phosphorylation was measured polarographically in brain mitochondria isolated from 1 to 3-week-old normal and triiodothyronine-treated rat pups. Adenosine diphosphate (ADP)/oxygen ratios with nicotinamide-adenine dinucleotide (NAD)-linked substrates, but not with succinate, were increased in brain mitochondria from experimental animals at each age. Control ratios and respiratory rates were not affected. Thus, the normal maturational increase in ADP/oxygen ratios with NAD-linked substrates is accelerated in brain mitochondria from rats treated with triiodothyronnie from birth. This effect on efficiency of oxidative phosphorylation is similar to that of throid hormones on other properties of the maturing brain.