Journal Article

Promoting effects of kojic acid due to serum TSH elevation resulting from reduced serum thyroid hormone levels on development of thyroid proliferative lesions in rats initiated with <i>N</i>-bis(2-hydroxypropyl)nitrosamine

Kunitoshi Mitsumori, Hiroshi Onodera, Masakazu Takahashi, Takushi Funakoshi, Toru Tamura, Kazuo Yasuhara, Kiyoshi Takegawa and Michihito Takahashi

in Carcinogenesis

Volume 20, issue 1, pages 173-176
Published in print January 1999 | ISSN: 0143-3334
Published online January 1999 | e-ISSN: 1460-2180 | DOI: http://dx.doi.org/10.1093/carcin/20.1.173
Promoting effects of kojic acid due to serum TSH elevation resulting from reduced serum thyroid hormone levels on development of thyroid proliferative lesions in rats initiated with N-bis(2-hydroxypropyl)nitrosamine

More Like This

Show all results sharing this subject:

  • Clinical Cytogenetics and Molecular Genetics

GO

Show Summary Details

Preview

In order to examine whether kojic acid (KA) exerts a promoting effect on thyroid carcinogenesis, male F344 rats were initiated with N-bis(2-hydroxypropyl)nitrosamine (BHP; 2800 mg/kg body wt, single s.c. injection) and, starting 1 week later, received pulverized basal diet containing 2 or 0% KA for 12 weeks. Untreated control rats were given basal diet for 13 weeks. As an additional experiment, two groups without BHP initiation received basal diet or diet containing 2% KA for 20 weeks. The serum triiodothyronine (T3) and thyroxine (T4) levels were significantly decreased (half to one-third of values of the BHP alone group) and serum thyroid-stimulating hormone (TSH) was markedly increased (13–19 times higher than the values of the BHP-alone group) in the BHP + KA group at weeks 4 and 12. Similar changes in serum thyroid-related hormones were observed in the group with 2% KA alone at week 4, but not at week 20. Thyroid weights were significantly increased in the BHP + KA and KA-alone groups. Focal thyroid follicular hyperplasias and adenomas were observed in 4/5 and 3/5 rats in the BHP + KA group at week 4, respectively. At weeks 12, these lesions were observed in all rats in the BHP + KA group. Animals of the KA alone group showed marked diffuse hypertrophy of follicular epithelial cells at weeks 4 and 20. No changes in thyroid-related hormone levels or thyroid histopathological lesions were observed in either the BHP alone or the untreated control groups. Measurement of liver T4-uridine diphosphate glucuronosyltransferase (UDP-GT) activity at week 4 revealed no significant intergroup differences. These results suggest that thyroid proliferative lesions were induced by KA administration due to continuous serum TSH stimulation through the negative feedback mechanism of the pituitary–thyroid axis, with decreases of T3 and T4 caused by a mechanism independent of T4-UDP-GT activity.

Keywords: BHP, N-bis(2-hydroxypropyl) nitrosamine; KA, kojic acid; PB, phenobarbital; PPO, polyphenoloxidase; PTU, propylthiouracil; T3, triiodothyronine; T4, thyroxine; TLC, thin-layer chromatography; TSH, thyroid-stimulating hormone; TU, thiourea; UDP-GT, T4-uridine diphosphate glucuronosyltransferase.

Journal Article.  3335 words.  Illustrated.

Subjects: Clinical Cytogenetics and Molecular Genetics

Full text: subscription required

How to subscribe Recommend to my Librarian

Users without a subscription are not able to see the full content. Please, subscribe or login to access all content.