Central Regulation of Hypothalamic-Pituitary-Thyroid Axis Under Physiological and Pathophysiological Conditions

TRH is a tripeptide amide that functions as a neurotransmitter but also serves as a neurohormone that has a critical role in the central regulation of the hypothalamic-pituitary-thyroid axis. Hypophysiotropic TRH neurons involved in this neuroendocrine process are located in the hypothalamic paraven...

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Bibliographic Details
Published in:Endocrine reviews 2014-04, Vol.35 (2), p.159-194
Main Authors: Fekete, Csaba, Lechan, Ronald M
Format: Article
Language:English
Subjects:
Adaptation, Physiological - physiology
Brittleness
Cerebrospinal fluid
Environmental changes
Environmental conditions
Feedback
Glial cells
Humans
Hypothalamic-pituitary-thyroid axis
Hypothalamus
Hypothalamus - physiology
Negative feedback
Neuroendocrine system
Neuronal-glial interactions
Neurons
Paraventricular nucleus
Physiological effects
Physiology
Pituitary (anterior)
Pituitary Gland - physiology
Reviews
Tanycytes
Thyroid
Thyroid gland
Thyroid Gland - physiology
Thyrotropin-releasing hormone
Thyrotropin-Releasing Hormone - physiology
Vascular system
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Summary:TRH is a tripeptide amide that functions as a neurotransmitter but also serves as a neurohormone that has a critical role in the central regulation of the hypothalamic-pituitary-thyroid axis. Hypophysiotropic TRH neurons involved in this neuroendocrine process are located in the hypothalamic paraventricular nucleus and secrete TRH into the pericapillary space of the external zone of the median eminence for conveyance to anterior pituitary thyrotrophs. Under basal conditions, the activity of hypophysiotropic TRH neurons is regulated by the negative feedback effects of thyroid hormone to ensure stable, circulating, thyroid hormone concentrations, a mechanism that involves complex interactions between hypophysiotropic TRH neurons and the vascular system, cerebrospinal fluid, and specialized glial cells called tanycytes. Hypophysiotropic TRH neurons also integrate other humoral and neuronal inputs that can alter the setpoint for negative feedback regulation by thyroid hormone. This mechanism facilitates adaptation of the organism to changing environmental conditions, including the shortage of food and a cold environment. The thyroid axis is also affected by other adverse conditions such as infection, but the central mechanisms mediating suppression of hypophysiotropic TRH may be pathophysiological. In this review, we discuss current knowledge about the mechanisms that contribute to the regulation of hypophysiotropic TRH neurons under physiological and pathophysiological conditions.
ISSN:0163-769X
1945-7189
1945-7189
DOI:10.1210/er.2013-1087