Reduced expression of renal Na+ transporters in rats with PTH-induced hypercalcemia

Weidong Wang, Chunling Li, Tae Hwan Kwon, R. Tyler Miller, Mark A. Knepper, Jørgen Frøkiær, Søren Nielsen

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Abstract

The purpose of this study was to evaluate whether the natriuresis and polyuria seen in parathyroid hormone (PTH)-induced hypercalcemia are associated with dysregulation of renal Na transporters. Rats were infused with three different doses of human PTH [PTH (1-34); 7.5, 10, and 15 μg·kg -1, sc] or vehicle for 48 h using osmotic minipumps. The rats treated with PTH developed significant hypercalcemia (plasma total calcium levels: 2.71 ± 0.03, 2.77 ± 0.02, and 3.42 ± 0.06 mmol/l, respectively, P < 0.05 compared with corresponding controls). The rats with severe hypercalcemia induced by high-dose PTH developed a decreased glomerular filtration rate (GFR), increased urine output, reduced urinary osmolality, increased urinary Na excretion, and fractional excretion of Na. This was associated with downregulation (calculated as a fraction of control levels) of whole kidney expression of type 2 Na-Pi cotransporter (NaPi-2; 16 ± 6%), type 3 Na/H exchanger (NHE3; 42 ± 7%), Na-K-ATPase (55 ± 2%), and bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1; 25 ± 4%). In contrast, an upregulation of the Ca2+-sensing receptor (CaR) was observed. Rats treated with moderate-dose PTH exhibited unchanged GFR but decreased urinary concentration. The whole kidney expression of NHE3 (52 ± 8%) and NaPi-2 (26 ± 5%) was persistently decreased, whereas BSC-1 and Na-K-ATPase protein levels were not altered. CaR expression was also increased. Moreover, rats treated with low-dose PTH showed very mild hypercalcemia but unchanged GFR, normal urinary concentration, and unchanged expression of Na transporters and CaR. In conclusion, the reduced expression of major renal Na transporters is likely to play a role in the increased urinary Na excretion and decreased urinary concentration in rats with PTH-induced hypercalcemia. Moreover, the increase in the CaR in the thick ascending limb (TAL) may indicate a potential role of the CaR in inhibiting Na transport in the TAL.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Renal Physiology
Volume286
Issue number3 55-3
StatePublished - Mar 2004

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Hypercalcemia
Parathyroid Hormone
Calcium-Sensing Receptors
Kidney
Glomerular Filtration Rate
Extremities
Bumetanide
Polyuria
Sodium-Hydrogen Antiporter
Natriuresis
Osmolar Concentration
Up-Regulation
Down-Regulation
Urine
Calcium

Keywords

  • Calcium-sensing receptor
  • Hypercalcemia
  • Parathyroid hormone
  • Sodium transport
  • Urinary concentrating mechanism

ASJC Scopus subject areas

  • Physiology

Cite this

Wang, W., Li, C., Kwon, T. H., Miller, R. T., Knepper, M. A., Frøkiær, J., & Nielsen, S. (2004). Reduced expression of renal Na+ transporters in rats with PTH-induced hypercalcemia. American Journal of Physiology - Renal Physiology, 286(3 55-3).

Reduced expression of renal Na+ transporters in rats with PTH-induced hypercalcemia. / Wang, Weidong; Li, Chunling; Kwon, Tae Hwan; Miller, R. Tyler; Knepper, Mark A.; Frøkiær, Jørgen; Nielsen, Søren.

In: American Journal of Physiology - Renal Physiology, Vol. 286, No. 3 55-3, 03.2004.

Research output: Contribution to journalArticle

Wang, W, Li, C, Kwon, TH, Miller, RT, Knepper, MA, Frøkiær, J & Nielsen, S 2004, 'Reduced expression of renal Na+ transporters in rats with PTH-induced hypercalcemia', American Journal of Physiology - Renal Physiology, vol. 286, no. 3 55-3.
Wang, Weidong ; Li, Chunling ; Kwon, Tae Hwan ; Miller, R. Tyler ; Knepper, Mark A. ; Frøkiær, Jørgen ; Nielsen, Søren. / Reduced expression of renal Na+ transporters in rats with PTH-induced hypercalcemia. In: American Journal of Physiology - Renal Physiology. 2004 ; Vol. 286, No. 3 55-3.
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abstract = "The purpose of this study was to evaluate whether the natriuresis and polyuria seen in parathyroid hormone (PTH)-induced hypercalcemia are associated with dysregulation of renal Na transporters. Rats were infused with three different doses of human PTH [PTH (1-34); 7.5, 10, and 15 μg·kg -1, sc] or vehicle for 48 h using osmotic minipumps. The rats treated with PTH developed significant hypercalcemia (plasma total calcium levels: 2.71 ± 0.03, 2.77 ± 0.02, and 3.42 ± 0.06 mmol/l, respectively, P < 0.05 compared with corresponding controls). The rats with severe hypercalcemia induced by high-dose PTH developed a decreased glomerular filtration rate (GFR), increased urine output, reduced urinary osmolality, increased urinary Na excretion, and fractional excretion of Na. This was associated with downregulation (calculated as a fraction of control levels) of whole kidney expression of type 2 Na-Pi cotransporter (NaPi-2; 16 ± 6{\%}), type 3 Na/H exchanger (NHE3; 42 ± 7{\%}), Na-K-ATPase (55 ± 2{\%}), and bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1; 25 ± 4{\%}). In contrast, an upregulation of the Ca2+-sensing receptor (CaR) was observed. Rats treated with moderate-dose PTH exhibited unchanged GFR but decreased urinary concentration. The whole kidney expression of NHE3 (52 ± 8{\%}) and NaPi-2 (26 ± 5{\%}) was persistently decreased, whereas BSC-1 and Na-K-ATPase protein levels were not altered. CaR expression was also increased. Moreover, rats treated with low-dose PTH showed very mild hypercalcemia but unchanged GFR, normal urinary concentration, and unchanged expression of Na transporters and CaR. In conclusion, the reduced expression of major renal Na transporters is likely to play a role in the increased urinary Na excretion and decreased urinary concentration in rats with PTH-induced hypercalcemia. Moreover, the increase in the CaR in the thick ascending limb (TAL) may indicate a potential role of the CaR in inhibiting Na transport in the TAL.",
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