Evidence for the rapid direct control both in vivo and in vitro of the efficiency of oxidative phosphorylation by 3,5,3′-tri-iodo-l-thyronine in rats

We report here investigations into some rapid effects of tri-iodothyronine on rat liver

R Palacios-Romero; J Mowbray

2015

Scholarcy highlights

  • In recent years there has been widespread recognition that much of the early work showing an effect of thyroxine on uncoupling oxidative phosphorylation was unphysiological
  • We report here investigations into some rapid effects of tri-iodothyronine on rat liver
  • The first objective was to examine the tissue distribution of tri-iodothyronine at short times after administration. This preliminary study focused attention very strongly on mitochondria, and the present paper describes some observations of a rapid effect of tri-iodothyronine both in vivo and in vitro on the efficiency of oxidative phosphorylation
  • Thyroidectomy was carried out in order to eliminate the presence of endogenous tri-iodothyronine or thyroxine and decrease competition for serum and cellular binding sites
  • As one aim of the work was to investigate the effects of tri-iodothyronine at short times after administration, the route taken by hormone between injection and killing of the animal could be crucial
  • Some loss of recovery was found when thetri-iodothyronine used for injection was investigated. This loss was never greater than 10% of applied radioactivity and was presumed to be the result of oxidation during chromatography
  • Since intravenous injection of tri-iodothyronine led to its rapid acquisition by mitochondria whose P/O ratio, impaired by thyroidectomy, was restored to normal within 15min, it was of obvious interest to investigate the effect of direct addition of hormone to preparations in vitro
  • Comparison of the effects of tri-iodothyronine found at short periods with those at the much longer times used by many other workers suggests that thyroid hormone could act at two different levels: one responsible for the primary effects of the hormone, such as an immediate action on microsomal or mitochondrial protein synthesis or on changes in ATP or energy production, though not all of these may be independent or primary effects; a second level might be adaptative responses to the hormone

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