Reversal of secondary hyperparathyroidism by phosphate restriction restores parathyroid calcium-sensing receptor expression and function.

Abstract

Secondary hyperparathyroidism (secondary HPT), a common disorder in chronic renal failure (CRF) patients, is characterized by hypersecretion of parathyroid hormone (PTH), parathyroid hyperplasia, and decreased expression of the calcium-sensing receptor (CaR). Dietary phosphate loading promotes secondary HPT, and phosphate restriction prevents and arrests secondary HPT in CRF. This study examined the ability of phosphate restriction to restore parathyroid CaR expression and function. Uremic rats fed a 1.2% P diet for 2 weeks developed secondary HPT with down-regulated CaR expression. Continuation on the 1.2% P diet for 2 more weeks worsened the secondary HPT and further decreased CaR, but switching the rats to a 0.2% P diet for 2 weeks normalized PTH, arrested parathyroid hyperplasia, and restored CaR expression to normal. The calcium-PTH relationship was abnormal in uremic rats fed a high phosphate (HP) diet with a right-shifted calcium set point but was corrected by 2 weeks of phosphate restriction. A time course revealed that following the switch to a low phosphate diet, PTH levels were normalized by day 1, and growth was arrested by day 2, but CaR expression was restored between days 7 and 14. We conclude that although phosphate restriction restores CaR expression and function in parathyroid glands of uremic rats, it is a late event and not involved in the arrest of secondary HPT.

• Authors: Cynthia S Ritter, Daniel R Martin, Yan Lu, Eduardo Slatopolsky, Alex J Brown
• Journal: Journal of bone and mineral research : the official journal of the American Society for Bone and Mineral Research (J Bone Miner Res) Vol. 17 Issue 12 Pg. 2206-13 (Dec 2002) ISSN: 0884-0431 [Print] United States
• PMID: 12469914 (Publication Type: Journal Article, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Phosphates
• Receptors, Calcium-Sensing
• Receptors, Cell Surface
• Receptors, Parathyroid Hormone
• extracellular calcium cation-sensing receptor, rat

Topics

• Animals
• Female
• Hyperparathyroidism, Secondary (prevention & control)
• Immunohistochemistry
• Phosphates (administration & dosage)
• Rats
• Rats, Sprague-Dawley
• Receptors, Calcium-Sensing
• Receptors, Cell Surface (metabolism)
• Receptors, Parathyroid Hormone (metabolism)