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Mechanistic data and risk assessment of selected toxic end points of the thyroid gland

C C Capen1

  • 1Department of Veterinary Biosciences, Ohio State University, Columbus 43210, USA.

Toxicologic Pathology
|January 1, 1997
PubMed

Insights

Many chemicals and physiological changes can disrupt thyroid hormone balance, leading to thyroid tumors in rodents. Chronic overstimulation by thyroid-stimulating hormone (TSH) is a key factor in this process.

Area of Science:

  • Endocrinology
  • Toxicology
  • Oncology

Background:

  • Goitrogenic xenobiotics and physiological changes can disrupt thyroid hormone homeostasis.
  • These disruptions affect thyroid hormone biosynthesis, secretion, metabolism, and peripheral conversion.
  • Chronic hormonal imbalances, particularly elevated thyroid-stimulating hormone (TSH), are linked to thyroid tumor development in rodents.

Purpose of the Study:

  • To elucidate the mechanisms by which goitrogens induce thyroid tumors in rodents.
  • To identify common pathways linking various goitrogenic agents to thyroid oncogenesis.
  • To highlight the role of chronic TSH stimulation in rodent thyroid tumor development.

Main Methods:

  • Review of existing literature on goitrogenic xenobiotics and physiological perturbations affecting the thyroid gland.
  • Analysis of mechanisms including direct effects on hormone synthesis and indirect effects via hepatic enzyme induction or altered hormone metabolism.
  • Examination of rodent studies demonstrating thyroid tumors following exposure to goitrogens or sustained hormonal imbalances.

Main Results:

  • Goitrogens disrupt thyroid hormone economy through direct effects on hormone synthesis/secretion or by increasing peripheral metabolism.
  • Inhibition of 5'-monodeiodinase (e.g., by FD&C Red No. 3) lowers T3, increasing TSH secretion.
  • Both xenobiotics and physiological perturbations consistently lead to chronic TSH hypersecretion, a key factor in rodent thyroid tumorigenesis.

Conclusions:

  • A consistent finding across diverse goitrogens is chronic TSH hypersecretion.
  • This sustained TSH stimulation is a secondary, indirect mechanism driving thyroid oncogenesis in rodents.
  • Understanding these pathways is crucial for assessing the carcinogenic potential of environmental and physiological factors affecting thyroid function.

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