Effects of in vivo and in vitro administered thyroxine on substrate metabolism of isolated rabbit ventricle mitochondria. II. Characteristics of oxidative phosphorylation in mitochondria of euthyroid, hyperthyroid and thyrotoxic rabbits.

Abstract

Twenty μg L-thyroxine was injected in vivo for a 1- to 31-day period into initially euthyroid rabbits, per day per 100 g body wt, followed by isolation and in vitro assays of the ventricle mitochondria. In the experiments of this paper no thyroxine was added in vitro. In the presence of added pyruvate + malate, the respiratory control ratio (RCR) slightly decreased after hormone treatment due to decelerated state 3 rate without any increase in the state 4 QO2, and irrespective of the in vitro availability of Mg++. Two techniques, alternatively applied for the isolation of mitochondria, yielded RCR's (with this substrate pair added) in the ranges of 7.0–18.0 and 3.0–7.0, respectively, the value dependent upon the in vitro conditions. The QO2's and the respiratory control ratio =2 with added succinate and =4 with octanoate were not altered by thyroxine administration. In the presence of added Mg++ the state 4 QO2 was raised by increased levels of added ATP, and was decreased by phosphoenolpyruvate + pyruvat...