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Central regulation of hypothalamic-pituitary-thyroid axis under physiological and
pathophysiological conditions
#MMPMID24423980
Fekete C
; Lechan RM
Endocr Rev
2014[Apr]; 35
(2
): 159-94
PMID24423980
show ga
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.
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