Short-term effects of triiodothyronine on the bowfin, Amia calva (Holostei), and the lake char, Salvelinus namaycush (Teleostei).

To assess the role of triiodothyronine (T3) in mediating short-term changes in metabolism, such as those occurring in circadian patterns, we examined the effects of intraperitoneal injection of T3 on the oxidation of substrates by isolated mitochondria from liver of the bowfin, Amia calva, and red muscle and liver of the lake char, Salvelinus namaycush. Selected enzymes were measured in red muscle and liver of the lake char. Three hours after intraperitoneal injection of T3, oxidation of some substrates by mitochondria isolated from the liver of the bowfin was reduced. Similar treatment had no effect on substrate oxidation in liver mitochondria isolated from lake char. Oxidation of substrates by lake char red muscle mitochondria was stimulated by T3 injection. Citrate synthase levels were increased in red muscle suggesting that changes in enzyme activity may be in part responsible for the short-term mitochondrial responses to T3 injection.