Calorigenic effect of diiodothyronines in the rat.

Abstract

1. In hypothyroid rats, we determined the effects of administration of different doses of 3,3',5-triiodo-L-thyronine (T3), 3,3'-diiodo-L-thyronine (3,3'-T2) and 3,5-diiodo-L-thyronine (3,5-T2) ('T2 isomers' refers specifically to these latter two isomers throughout this paper) on resting metabolism (RM) and on the oxidative capacity (measured as cytochrome oxidase activity) of tissues that are metabolically very active. 2. The T2 isomers induced a dose-dependent calorigenic effect when injected i.P. into hypothyroid rats. The increase in RM was already evident at a dose of 2 5 ,sg (100 g body wt)-', and the greatest effect was observed at the highest dose, 10 ,ug (100 g body wt)-, when RM reached a value not significantly different from that of the euthyroid controls (1X92 + 0-08 and 1P93 + 0-13 (1 02) kg-' h-' for 3,5-T2 and 3,3'-T2, respectively, vs. 2 1 + 0-12 (1 02) kg-1 h-' for euthyroid controls). T3 administration restored RM to normal euthyroid values, even at a dose of 2-5 ,ug (100 g body wt)-1. 3. The effect of T2 isomers on RM was paralleled by an increase in the oxidative capacity of tissues that are metabolically very active (liver, skeletal muscle, brown adipose tissue (BAT) and heart). The increases were between 33% (liver + 3,3'-T2) and 63% (muscle + 3,3'-T2). By contrast, T3 induced its greatest effect on the liver, with a smaller effect on skeletal muscle, but no significant stimulation in heart and BAT, whatever the dose. 4. These results suggest that T2 isomers might regulation of energy metabolism.

Triiodothyronine induces lipid oxidation and mitochondrial biogenesis in rat Harderian gland

“…In addition, the rats received an i.p. injection of iopanoic acid (IOPA; 6 mg/100 g body weight) (Lanni et al 1996) once a week. PTU blocks thyroidal hormone synthesis via inhibition of thyroid peroxidase activity, and it is also a strong inhibitor of type I 5 0 -D-deiodinase activity (Oppenheimer et al 1972, Leonard & Visser 1986.…”

Uncoupling protein 2 mRNA expression and respiratory parameters in Kupffer cells isolated from euthyroid and hyperthyroid rat livers

“…Resting metabolism was measured by indirect calorimetry, as previously reported (27) and thyroid hormone serum levels were measured by radioimmunoassay (Becton-Dickinson, Orangenburg, NJ, USA).…”

Morphological and biochemical changes in the Harderian gland of hypothyroid rats

“…In addition, since we found that some morphological signs are indicative of cell death by apoptosis, we compared both mitochondrial and cytosolic expression of cytochrome c [the principal initiator molecule released from mitochondria to cytosol to initiate the apoptotic program in cells (Green and Reed, 1998)] in euthyroid and hypothyroid rat HGs. (Lanni et al, 1996). Control rats (N=8) received saline injections.…”