AJP - Endocrinology and Metabolism, Vol 263, Issue 1 E115-E120, Copyright © 1992 by American Physiological Society
Decreased T4-to-T3 conversion in brown adipose tissue of Zucker fa/fa pups before the onset of obesity
V. Marie, F. Dupuy and R. Bazin
Institut National de la Sante et de la Recherche Medicale, Unite 177, Paris, France.
To determine whether the capacity of thyroxine
(T4)-to-3,5,3'-triiodothyronine (T3) conversion was altered in Zucker fa/fa
pups, we measured thyroxine 5'-monodeiodinase (T(4)5'D) activity in brown
adipose tissue (BAT) and liver of suckling and weaned fa/fa and Fa/fa
littermates. In suckling fa/fa compared with Fa/fa rats, T(4)5'D was
reduced by 30-55% in BAT and slightly increased in liver, while serum free
T3 was significantly decreased (-30%). Altered T(4)5'D activity in BAT of
fa/fa pups could be corrected by adrenergic stimulation. After weaning, in
fa/fa rats, the capacity for T4-to-T3 conversion was totally restored in
BAT while it was dramatically reduced in liver. The concentration of serum
free T3 remained lower in fa/fa than in Fa/fa rats (-40%). These data
confirm that BAT is a very early site of fa gene expression and are
consistent with the hypothesis that a defect in the autonomic nervous
system may be a primary cause of this genetic obesity. It is also suggested
that, during suckling, BAT plays an important role in systemic production
of T3.
