AJP - Endocrinology and Metabolism, Vol 273, Issue 2 E247-E253, Copyright © 1997 by American Physiological Society
Effects of triiodothyronine administration on the adenylyl cyclase system in brown adipose tissue of rat
H. Adli, R. Bazin, R. Vassy and G. Y. Perret
Laboratoire de Pharmacologie Clinique et Experixentale, Faculte de Medecine, Universite Paris Nord, Bobigny, France.
This study was undertaken to investigate the effect of triiodothyronine
(T3) administration to euthyroid rats on beta 3-adrenoceptor (beta 3-AR)
expression and on the different components of the adenylyl cyclase (AC)
system in brown adipose tissue (BAT). In rats treated with T3, the beta
3-AR density (assessed by the binding of [3H]CGP-12177) showed a decrease
of 50%, as did their mRNA, as analyzed by reverse transcriptase-polymerase
chain reaction. In hyperthyroid rats, compared with control rats, there was
a 40% increase in G alpha s activity (stimulated by NaF or GTP gamma S) and
a fourfold increase in the protein concentration (Western blotting). In
contrast, the level of the pertussis toxin substrate Gi declined by 35% in
response to T3. Analysis of dose-response curves for isoproterenol and
CGP-12177 revealed that neither basal nor stimulated AC activities nor 50%
stimulatory concentration for these agonists was changed by T3
administration. In conclusion, these results suggest that downregulation of
the beta 3-AR by T3 was counter-balanced by changes in other components of
the AC cascade (i.e., Gs and Gi), so no change occurred in the capacity of
BAT to generate adenosine 3',5'-cyclic monophosphate.
