Analysis of Nuclear 3,3',5-Triiodothyronine Receptor in the Brown Adipose Tissue (BAT) of the Postnatal Lamb

S. Y. Wu; J. K. Kim; D. T. Tjioe; W. S. Huang; I. J. Chopra

doi:10.1055/s-2007-1003349

Hormone and Metabolic Research, Table of Contents

Horm Metab Res 1992; 24(9): 416-419
DOI: 10.1055/s-2007-1003349

Originals Basic

Analysis of Nuclear 3,3',5-Triiodothyronine Receptor in the Brown Adipose Tissue (BAT) of the Postnatal Lamb

S. Y. Wu¹ , J. K. Kim¹ , D. T. Tjioe² , W. S. Huang³ , I. J. Chopra⁴

¹Nuclear Medicine and Medical Services, Veterans Administration Medical Center, Long Beach, and University of California, Irvine
²Department of Anatomy and Physiology, California State University, Long Beach, U. S. A.
³Department of Nuclear Medicine, Tri-Service General Hospital and National Defense Medical Center, Taipei, Taiwan, ROC
⁴Department of Medicine, UCLA School of Medicine, Los Angeles, California, USA

Abstract

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Summary

Postnatal thermogenesis in sheep is associated with increased sympathoadrenal activities, a T₃ surge and an enhanced brown adipose tissue (BAT) type II 5'-monodeiodinating (5'-MDI) activity. The latter peaks 3-4 days after birth and is known to be important in generating intracellular T₃ for nuclear receptor binding. In order to further investigate the mechanism(s) responsible for neonatal thermogenesis, thyroid hormone nuclear receptor (T₃NR) binding characteristics were quantified in lamb BAT from newborn (NB) to 30d of postnatal age. Maximal binding capacities (MBC, mean±SEM fmoles T₃/mg DNA) in BAT showed a decrease as studied by ANOVA during the first 11 days (NB to Id, 148±24 [N = 5, p < 0.01, cf.3-5d group];3-5d, 61±5.5[N = 5]; 10-11d, 72±9.1 [N = 4]). Afterwards, MBC increased at 30d (196±32, N = 4, p < 0.01, cf. 3-5d group). BAT T₃NR binding affinities (10⁹ M^-1 were comparable in all age groups studied (NB-1d, 2.8±0.3; 3-5d, 3.4±0.3; 10-11d, 4.0±1.1; 30d, 2.4±0.4). The data suggest that the postnatal surge in T₃ and type II 5'-MDI is accompanied with a concurrent decrease in MBC of BAT T₃NR. The latter may represent a down-regulation of T₃NR presumably in an attempt to regulate the overall effect of thyroid hormone in neonatal thermogenesis.

Key words

Triiodothyronine (T₃) - Nuclear Receptor - Brown Fat - Lambs

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