Vol. 274, Issue 2, E238-E245, February 1998
Acute effects of thyroid hormones on the production of adrenal
cAMP and corticosterone in male rats
Ming-Jae
Lo1,
Mei-Mei
Kau1,
Yen-Hao
Chen2,
Shiow-Chwen
Tsai1,
Yu-Chung
Chiao1,
Jiann-Jong
Chen1,
Charlie
Liaw1,
Chien-Chen
Lu1,
Bu-Pian
Lee1,
Si-Chih
Chen2,
Victor S.
Fang3,
Low-Tone
Ho3, and
Paulus S.
Wang1
1 Department of Physiology,
National Yang-Ming University, Taipei 112;
2 Department of Biology,
Fu-Jen Catholic University, Taipei 242; and
3 Department of Medical Research
and Education, Veterans General Hospital-Taipei, Taipei 112, Taiwan, Republic of China
The acute effects of
thyroid hormones on glucocorticoid secretion were studied. Venous blood
samples were collected from male rats after they received intravenous
3,5,3'-triiodothyronine
(T3) or thyroxine
(T4). Zona
fasciculata-reticularis (ZFR) cells were treated with
adrenocorticotropic hormone (ACTH),
T3,
T4, ACTH plus
T3, or ACTH plus
T4 at 37°C for 2 h.
Corticosterone concentrations in plasma and cell media, and also
adenosine 3',5'-cyclic monophosphate (cAMP) production in
ZFR cells in the presence of 3-isobutyl-1-methylxanthine, were
determined. The effects of thyroid hormones on the activities of
steroidogenic enzymes of ZFR cells were measured by the amounts of
intermediate steroidal products separated by thin-layer chromatography. Administration of T3 and
T4 suppressed the basal and the
ACTH-stimulated levels of plasma corticosterone. In ZFR cells, both
thyroid hormones inhibited ACTH-stimulated corticosterone secretion,
but the basal corticosterone was inhibited only with
T3
>10
10 M or
T4
>108 M. Likewise,
T3 or
T4 at
107 M inhibited the basal-
and ACTH-stimulated levels of intracellular cAMP. Physiological doses
of T3 and
T4 decreased the activities of
3
-hydroxysteroid dehydrogenase, 21-hydroxylase, and
11-hydroxylase. These results suggest that thyroid hormones
counteract ACTH in adrenal steroidogenesis through their inhibition of
cAMP production in ZFR cells.
3,5,3'-triiodothyronine; thyroxine; zona
fasciculata-reticularis cells; P450c11 activity; adenosine
3',5'-cyclic monophosphate
