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. 2022 Dec 6;14(23):5186. doi: 10.3390/nu14235186

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© 2022 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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Parathyroid-kidney axis. Parathyroid hormone (PTH) secretion from the parathyroid gland is increased in response to a decrease in ionized plasma calcium (Ca) or to an increase in the blood concentration of inorganic phosphate (P). PTH binds to the parathyroid hormone-1 receptor (PTH1R) in proximal tubules (PT) of the kidney, promoting 1,25(OH)₂D production by upregulating 1α-hydroxylase (Cyp27B1) and suppressing 24-hydroxylase (Cyp24A1) expression. As part of a feedback inhibition, 1,25(OH)₂D downregulates its own production by stimulating Cyp24A1 and inhibiting Cyp27B1 expression in the kidney. Circulating 1,25(OH)₂D signals back to the parathyroid gland, where it inhibits PTH transcription and secretion. Arrows indicate the direction and nature of regulation (green, stimulation; red, inhibition). Created with BioRender.com.(Biorender 2022, Toronto, Ontario, Canada).