Influence of thyroidectomy on thyroxine metabolism and turnover rate in rats.
J Endocrinol
; 210(1): 117-23, 2011 Jul.
Article
em En
| MEDLINE
| ID: mdl-21478227
ABSTRACT
Little is known about the kinetics and metabolism of thyroid hormones in the hypothyroid state. To investigate these factors, we developed a reliable method for measurement of serum thyroxine (T(4)), triiodothyronine (T(3)), reverse-T(3) (rT(3)) and stable isotope-labeled T(4) ([(13)C(9)]T(4)), using online solid-phase extraction liquid chromatography-mass spectrometry/mass spectrometry (online SPE LC-MS/MS). We measured supply and turnover rates of T(4) in thyroidectomized (Tx) rats using [(13)C(9)]T(4) as a tracer. In rats, serum T(4), T(3) and rT(3) were decreased but not completely ablated after surgical Tx. Endogenous T(4) and T(3) levels in Tx rats were maintained at a constant low level throughout the experimental period. [(13)C(9)]T(4) levels declined with a half-life of â¼1.2 days after it was administered to Tx rats intravenously. These findings strongly suggest that serum T(4) levels in Tx rats are maintained by T(4) supplied by extra-thyroidal tissues (e.g. secretion of extra-thyroidal storage, enhancement of enterohepatic recirculation, and production in extra-thyroidal tissues). Moreover, the turnover rate of T(4) in Tx rats was approximately twofold lower than in controls. This finding suggests that degradation of serum T(4) is repressed by Tx. In conclusion, serum T(4) is maintained at a constant low level by T(4) supply from extra-thyroidal tissues and repression of T(4) degradation in Tx rats. The powerful online SPE LC-MS/MS tool can be used to investigate thyroid hormones kinetics and metabolism, and thus has the potential to be used as a diagnostic tool and to investigate the pathogenesis of thyroid disease.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Tireoidectomia
/
Tiroxina
/
Hipotireoidismo
Limite:
Animals
Idioma:
En
Revista:
J Endocrinol
Ano de publicação:
2011
Tipo de documento:
Article