AJP - Endocrinology and Metabolism, Vol 252, Issue 1 E63-E67, Copyright © 1987 by American Physiological Society
Cold-induced increase in brown fat thyroxine 5'-monodeiodinase is attenuated in Zucker obese rat
S. Y. Wu, J. S. Stern, D. A. Fisher and Z. Glick
In this study we examined the possibility that the reduced brown adipose
tissue (BAT) thermogenesis in the Zucker obese rat may result from a
limited capacity for enzymic conversion of thyroxine (T4) to
triiodothyronine (T3) in BAT. A total of 34 lean and obese rats,
approximately 4 mo old were divided into three treatment groups: group 1 (5
lean and 6 obese) was fed Purina rat chow for 21 days, and group 2 (5 lean
and 6 obese) was fed a cafeteria diet for 21 days, and group 3 (6 lean and
6 obese) was fed Purina rat chow and maintained in the cold (8 +/- 1
degrees C) for 7 days. The lean and obese rats in all three groups of
animals were matched closely for age and respective body weight. Activity
of T4 5'-deiodinase was determined as the rate of T3 production from added
T4 under controlled in vitro conditions. Serum T4 and T3 were determined by
radioimmunoassay. The rate of T4-to-T3 conversion in BAT was similar in the
lean and obese rats maintained at room temperature, whether fed rat chow or
a cafeteria diet (approximately 40-50 pmol T3/scapular BAT depot per h).
However, expressed per scapular BAT depot, lean rats exposed to cold
displayed about a fivefold increase in BAT T3 production (P less than
0.0001), whereas only a small increase was observed in the cold-exposed
obese rats. Serum T3 levels tended to be reduced in the Zucker obese rats.
Our data indicate a reduced capacity for T3 production in Zucker rat BAT
exposed to cold.(ABSTRACT TRUNCATED AT 250 WORDS)
