The Neuroendocrine System and General Mechanisms of Endocrine Disruption

2017 ◽  
Author(s):  
Heather B. Patisaul ◽  
Scott M. Belcher
Keyword(s):  
Feedback Regulation ◽  
Neuroendocrine System ◽  
Negative Feedback Regulation ◽  
Adrenal Hormone ◽  
Aryl Hydrocarbon ◽  
Pituitary Thyroid Axis ◽  
Thyroid Axis ◽  
Environmental Sensor ◽  
Exogenous Compounds ◽  
Primary Focus

The neuroendocrine system is the interface between the endocrine and nervous systems. This chapter presents an overview of the neuroendocrine system and endogenous hormones, with a primary focus on the hypothalamic-pituitary-gonadal (HPG) axis, the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-thyroid axis (HPT). The importance of impacts of exogenous compounds, both natural and man-made, on the neuroendocrine system is discussed, with a focus on endocrine-disruptive actions of plant-derived phytoestrogens and the role of the aryl hydrocarbon receptor as an environmental sensor. The impacts of EDCs on feed-forward and negative feedback regulation of neuroendocrine functions, including those mediated by estrogen, androgen, and thyroid pathways, as well as other less studied pathways of hormonal signaling that involve disruption of neurosteroids, peptide hormones, and adrenal hormone signaling are also presented.

scholarly journals MECHANISMS IN ENDOCRINOLOGY: Beyond the fixed setpoint of the hypothalamus–pituitary–thyroid axis

2014 ◽  
Vol 171 (5) ◽  
pp. R197-R208 ◽  
Author(s):  
Eric Fliers ◽  
Andries Kalsbeek ◽  
Anita Boelen
Keyword(s):  
Thyroid Hormone ◽  
Negative Feedback ◽  
Thyroid Hormone Receptor ◽  
Feedback Regulation ◽  
Tissue Level ◽  
Serum Concentrations ◽  
Negative Feedback Regulation ◽  
Pituitary Thyroid Axis ◽  
Thyroid Axis ◽  
Hpt Axis

The hypothalamus–pituitary–thyroid (HPT) axis represents a classical example of an endocrine feedback loop. This review discusses dynamic changes in HPT axis setpoint regulation, identifying their molecular and cellular determinants, and speculates about their functional role. Hypothalamic thyrotropin-releasing hormone neurons were identified as key components of thyroid hormone (TH) setpoint regulation already in the 1980s, and this was followed by the demonstration of a pivotal role for the thyroid hormone receptor beta in negative feedback of TH on the hypothalamic and pituitary level. Gradually, the concept emerged of the HPT axis setpoint as a fixed entity, aiming at a particular TH serum concentration. However, TH serum concentrations appear to be variable and highly responsive to physiological and pathophysiological environmental factors, including the availability or absence of food, inflammation and clock time. During food deprivation and inflammation, TH serum concentrations decrease without a concomitant rise in serum TSH, reflecting a deviation from negative feedback regulation in the HPT axis. Surprisingly, TH action in peripheral organs in these conditions cannot be simply predicted by decreased serum TH concentrations. Instead, diverse environmental stimuli have differential effects on local TH metabolism, e.g. in liver and muscle, occurring quite independently from decreased TH serum concentrations. The net effect of these differential local changes is probably a major determinant of TH action at the tissue level. In sum, hypothalamic HPT axis setpoint regulation as well as TH metabolism at the peripheral organ level is flexible and dynamic, and may adapt the organism in an optimal way to a range of environmental challenges.

The Role of Tanycytes in the Hypothalamus-Pituitary-Thyroid Axis and the Possibilities for Their Genetic Manipulation

2019 ◽  
Vol 128 (06/07) ◽  
pp. 388-394
Author(s):  
Helge Müller-Fielitz ◽  
Markus Schwaninger
Keyword(s):  
Energy Homeostasis ◽  
Genetic Manipulation ◽  
Heart Function ◽  
Feedback Regulation ◽  
Target Organs ◽  
Pituitary Thyroid Axis ◽  
Thyroid Axis ◽  
Hpt Axis ◽  
The Brain

AbstractThyroid hormone (TH) regulation is important for development, energy homeostasis, heart function, and bone formation. To control the effects of TH in target organs, the hypothalamus-pituitary-thyroid (HPT) axis and the tissue-specific availability of TH are highly regulated by negative feedback. To exert a central feedback, TH must enter the brain via specific transport mechanisms and cross the blood-brain barrier. Here, tanycytes, which are located in the ventral walls of the 3rd ventricle in the mediobasal hypothalamus (MBH), function as gatekeepers. Tanycytes are able to transport, sense, and modify the release of hormones of the HPT axis and are involved in feedback regulation. In this review, we focus on the relevance of tanycytes in thyrotropin-releasing hormone (TRH) release and review available genetic tools to investigate the physiological functions of these cells.

Effects of Food Deprivation on the Feedback Regulation of the Hypothalamic-Pituitary-Thyroid Axis of the Rat*

Endocrinology ◽  
1985 ◽  
Vol 117 (3) ◽  
pp. 900-906 ◽  
Author(s):  
JOHN M. CONNORS ◽  
WILLIAM J. DEVITO ◽  
GEORGE A. HEDGE
Keyword(s):  
Food Deprivation ◽  
Feedback Regulation ◽  
Pituitary Thyroid Axis ◽  
Thyroid Axis

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

2013 ◽  
Vol 35 (2) ◽  
pp. 159-194 ◽  
Author(s):  
Csaba Fekete ◽  
Ronald M. Lechan
Keyword(s):  
Thyroid Hormone ◽  
Negative Feedback ◽  
Vascular System ◽  
Current Knowledge ◽  
Critical Role ◽  
Central Regulation ◽  
Negative Feedback Regulation ◽  
External Zone ◽  
Pituitary Thyroid Axis ◽  
Thyroid Axis

Abstract 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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