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Hypocalcemia, but not PTH or hypophosphatemia, induces a rapid increase in 1,25(OH)2D3 levels in rats.
Am J Physiol. 1992 Feb; 262(2 Pt 1):E211-5.AJ

Abstract

This study determined whether acute decreases in plasma ionized calcium (Ca2+) levels regulate plasma 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels independent of changes in parathyroid hormone (PTH) secretion and plasma phosphate levels. Chronically catheterized rats were subjected to a hypocalcemic clamp (mean decrement of Ca2+ levels 0.38 +/- 0.04 mM), a rat PTH-(1-34) infusion, and a PTH vehicle infusion for 2 h. Plasma NH2-terminal immunoreactive PTH levels were elevated 3.2- and 8.7-fold during hypocalcemia and PTH infusion, respectively. Plasma phosphate decreased by 23 +/- 4 and 42 +/- 3% during hypocalcemia and PTH infusion, respectively. In response to hypocalcemia, plasma 1,25(OH)2D3 levels increased promptly, were significantly elevated by 15 min (56 +/- 23% increase), and continued to increase until the end of the experiment at 5 h (350 +/- 30% increase). In contrast, no changes in plasma 1,25(OH)2D3 levels occurred during the PTH infusion, but levels were elevated by 5 h, i.e., 3 h after the end of the infusion (360 +/- 20% increase). No significant changes in 25(OH)D3 or 24,25(OH)2D3 levels occurred in any protocol. Thus hypocalcemia rapidly elevates 1,25(OH)2D3 levels in rats, but the increase is not caused by elevated PTH secretion, hypophosphatemia, or elevated 25(OH)D3 levels. Furthermore, the increase in 1,25(OH)2D3 levels by hypophosphatemia does not occur rapidly. These studies show that there is a calcium-dependent mechanism that is independent of changes in PTH secretion and that results in the rapid elevation of plasma 1,25(OH)2D3 levels to counteract hypocalcemia.

Authors+Show Affiliations

Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

1539647

Citation

Fox, J. "Hypocalcemia, but Not PTH or Hypophosphatemia, Induces a Rapid Increase in 1,25(OH)2D3 Levels in Rats." The American Journal of Physiology, vol. 262, no. 2 Pt 1, 1992, pp. E211-5.
Fox J. Hypocalcemia, but not PTH or hypophosphatemia, induces a rapid increase in 1,25(OH)2D3 levels in rats. Am J Physiol. 1992;262(2 Pt 1):E211-5.
Fox, J. (1992). Hypocalcemia, but not PTH or hypophosphatemia, induces a rapid increase in 1,25(OH)2D3 levels in rats. The American Journal of Physiology, 262(2 Pt 1), E211-5.
Fox J. Hypocalcemia, but Not PTH or Hypophosphatemia, Induces a Rapid Increase in 1,25(OH)2D3 Levels in Rats. Am J Physiol. 1992;262(2 Pt 1):E211-5. PubMed PMID: 1539647.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Hypocalcemia, but not PTH or hypophosphatemia, induces a rapid increase in 1,25(OH)2D3 levels in rats. A1 - Fox,J, PY - 1992/2/1/pubmed PY - 1992/2/1/medline PY - 1992/2/1/entrez SP - E211 EP - 5 JF - The American journal of physiology JO - Am. J. Physiol. VL - 262 IS - 2 Pt 1 N2 - This study determined whether acute decreases in plasma ionized calcium (Ca2+) levels regulate plasma 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] levels independent of changes in parathyroid hormone (PTH) secretion and plasma phosphate levels. Chronically catheterized rats were subjected to a hypocalcemic clamp (mean decrement of Ca2+ levels 0.38 +/- 0.04 mM), a rat PTH-(1-34) infusion, and a PTH vehicle infusion for 2 h. Plasma NH2-terminal immunoreactive PTH levels were elevated 3.2- and 8.7-fold during hypocalcemia and PTH infusion, respectively. Plasma phosphate decreased by 23 +/- 4 and 42 +/- 3% during hypocalcemia and PTH infusion, respectively. In response to hypocalcemia, plasma 1,25(OH)2D3 levels increased promptly, were significantly elevated by 15 min (56 +/- 23% increase), and continued to increase until the end of the experiment at 5 h (350 +/- 30% increase). In contrast, no changes in plasma 1,25(OH)2D3 levels occurred during the PTH infusion, but levels were elevated by 5 h, i.e., 3 h after the end of the infusion (360 +/- 20% increase). No significant changes in 25(OH)D3 or 24,25(OH)2D3 levels occurred in any protocol. Thus hypocalcemia rapidly elevates 1,25(OH)2D3 levels in rats, but the increase is not caused by elevated PTH secretion, hypophosphatemia, or elevated 25(OH)D3 levels. Furthermore, the increase in 1,25(OH)2D3 levels by hypophosphatemia does not occur rapidly. These studies show that there is a calcium-dependent mechanism that is independent of changes in PTH secretion and that results in the rapid elevation of plasma 1,25(OH)2D3 levels to counteract hypocalcemia. SN - 0002-9513 UR - https://www.unboundmedicine.com/medline/citation/1539647/Hypocalcemia_but_not_PTH_or_hypophosphatemia_induces_a_rapid_increase_in_125_OH_2D3_levels_in_rats_ L2 - http://www.physiology.org/doi/full/10.1152/ajpendo.1992.262.2.E211?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -