AJP - Endocrinology and Metabolism, Vol 251, Issue 5 503-E508, Copyright © 1986 by American Physiological Society
Brown fat nuclear triiodothyronine receptors in rats
U. Burgi and M. E. Burgi-Saville
Brown adipose tissue (BAT) thermogenesis is important in the adaptation of
body energy expenditure to cold exposure, fasting, and overfeeding and in
the pathogenesis of obesity. Thyroid hormones are required for the normal
functioning of BAT. The mechanism of their effect on BAT, however, has not
yet been elucidated. Since most thyroid hormone effects are mediated via
the binding of T3 to nuclear receptors (NT3R) the present studies were
performed to investigate whether BAT contained NT3R and whether these NT3R
were affected by cold exposure, fasting, overfeeding, or hypo- or
hyperthyroidism. Rat BAT was found to contain NT3R with a maximum binding
capacity (MBC) of 0.28 ng T3/mg DNA and a dissociation constant (Kd) of 3.2
X 10(-10) M. These parameters were unaffected by any of the experimental
conditions studied. A major alteration of BAT NT3R MBC or Kd is thus not a
causal factor in the changes in BAT thermogenesis induced by the above
experimental conditions. In contrast, 3-wk overfeeding increased (+48%) and
fasting decreased (-29%) the MBC of hepatic NT3R. Overfeeding increased
serum T3 (+110%), while fasting decreased it (-37%).
