The physiological functions
of Thyroid Stimulating Hormone
(TSH) auto regulation, the ultra-short feedback loop inhibition of TSH by TSH itself, have not been determined. In this work we explored the role of TSH auto regulation in thyroid homeostasis. We synthesized the known physiology of auto regulation with the known physiological relationships
between thyroid hormones; in particular between free thyroxin and TSH. We analyzed the implications of TSH auto regulation, on the generation of the TSH response to free thyroxin (the ‘TSH curve’), and on the variation in this response, which might result from variations in hypothalamopituitary or thyroid gland function. Our analysis demonstrated that, in the circumstances of inter-individual and intra-individual variations to hypothalamus-pituitary function TSH auto regulation lessens variation in the TSH curve. This in turn enhances the probability of generating and maintaining a euthyroid free thyroxin value. This contribution of TSH auto regulation to the stabilization of thyroid physiology offers a logical explanation for the evolutionary selection of this physiological process.
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