parathyroid hormone; parathormone; parathyrin (PTH)

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Function

PTH is secreted by chief cells of the parathyroid gland in response to a decrease in plasma Ca+2 or an increase in plasma phosphate
PTH increases plasma Ca+2 & lowers plasma phosphate by:
- increasing Ca+2 resorption in the distal renal tubules, thus reducing urinary Ca+2 excretion
- enhancing urinary phosphate excretion
- stimulating bone resorption
- promoting renal production of 1,25 dihydroxy vitamin D3, thus increasing gastrointestinal absorption of Ca+2
circadian rhythm is present with highest plasma levels at 1400-1600 hours & lowest levels at 0800 hours
normal 1/2 life of intact PTH (1-84) is 5 minutes
inactive C-terminal & mid-molecule fragments (i.e. fragments 53-84, 44-68 & 35-64) make up 90% of circulating PTH metabolites
- these fragments are cleared by the kidneys with a 1/2 life of 1-2 hours
a circulating amino-terminal fragment (i.e. fragment 1-34) has a 1/2 life of 1-2 minutes
interacts with PTH1R (via N-terminal extracellular domain)
only the intact & N-terminal fragments have biological activity
intact & N-terminal fragments are removed from plasma by renal excretion & other mechanisms
stimulates 2-deoxy-D-glucose (2DG) transport & glycogen synthesis in osteoblastic cells

belongs to the parathyroid hormone family

↑ Clinical Diagnosis & Management by Laboratory Methods, J.B. Henry (ed), W.B. Saunders Co., Philadelphia, PA. 1991, pg 154
↑ Cotran et al Robbins Pathologic Basis of Disease, W.B. Saunders Co, Philadelphia, PA 1989 pg 1242
↑ Cotran et al Robbins Pathologic Basis of Disease, 5th ed. W.B. Saunders Co, Philadelphia, PA 1994 pg 1143
↑ UniProt http://www.uniprot.org/uniprot/P01270.html
↑ Wikipedia; Note: parathyroid hormone entry http://en.wikipedia.org/wiki/parathyroid_hormone