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[Dopaminergic and somatostatinergic pathways decrease serum thyrotropin in rats bearing the 256-Walker mammary
Osmar Monte1, Szulin Zyngier, Edna T Kimura
1Departamento de Ciências Fisiológicas, Faculdade de Ciências Médicas da Santa Casa de São Paulo.
Arquivos Brasileiros De Endocrinologia E Metabologia
|September 27, 2005
Summary
Walker-256 tumor implantation in rats induced low triiodothyronine (T3) syndrome, significantly reducing thyroid activity and thyroid-stimulating hormone (TSH) secretion. Metoclopramide and physostigmine partially restored TSH response to thyrotropin-releasing hormone (TRH).
Area of Science:
- Endocrinology
- Oncology
- Physiology
Background:
- The hypothalamus-pituitary-thyroid (HPT) axis regulates thyroid hormone production.
- Cancer cachexia, like that induced by Walker-256 mammary carcinoma, can disrupt endocrine function.
- Low triiodothyronine (T3) syndrome is a condition associated with various illnesses, including cancer.
Purpose of the Study:
- To investigate the impact of Walker-256 mammary carcinoma implantation on the HPT axis in rats.
- To determine the effects of metoclopramide and physostigmine on TSH secretion in tumor-bearing rats.
Main Methods:
- Walker-256 mammary carcinoma cells were implanted in male adult rats.
- Thyroid activity, serum T4 and rTg levels, and TSH secretion in response to TRH were measured.
- Tumor-bearing rats were treated with metoclopramide and/or physostigmine, with or without TRH stimulation.
Main Results:
- Tumor development led to decreased thyroid activity, including reduced thyrocyte nuclear area, 131I-thyroid uptake, and serum T4 and rTg levels.
- TSH secretion in response to TRH was significantly blunted in tumor-bearing rats.
- Metoclopramide and physostigmine administration improved the TSH response to TRH, with combined administration normalizing it.
Conclusions:
- Walker-256 tumor implantation induces a generalized reduction in thyroid function, characterized by decreased TSH secretion.
- Hypothalamic neuromediators, modulated by metoclopramide and physostigmine, play a role in regulating TSH secretion during cancer-induced low T3 syndrome.