INTRODUCTION: Thiazide diuretics have the unique characteristic of increasing renal Na+ excretion, while decreasing Ca2+ excretion. However, the molecular mechanism responsible for this thiazide-induced hypocalciuria remains unclear. The present study investigates the effect of thiazides on the expression of the proteins involved in active Ca2+ transport as well as the role of extracellular volume (ECV) status. METHODS: Hydrochlorothiazide (HCTZ), 12 mg/24 hours, was administered during 7 days to Wistar rats by osmotic minipumps. In addition, ECV contraction was either prevented by Na+ repletion or induced by a low-salt diet. Expression levels of the proteins involved in active Ca2+ transport [i.e., epithelial Ca2+ channel (TRPV5/ECaC1), calbindin-D28K, Na+/Ca2+ exchanger (NCX1)], as well as the thiazide-sensitive Na+ Cl- cotransporter (NCC) were determined by real-time quantitative polymerase chain reaction (PCR) and semiquantitative immunohistochemistry. RESULTS: HCTZ significantly reduced urinary Ca2+ excretion (22%+/- 5% relative to controls). Hematocrit was significantly increased, confirming ECV contraction. In addition, Na+ depletion virtually abolished Ca2+ excretion (8%+/- 1%), while Na+ repletion during HCTZ treatment prevented both ECV contraction and hypocalciuria. HCTZ significantly decreased mRNA expression of TRPV5 (71%+/- 6%), calbindin-D28K (53%+/- 6%), NCX1 (51%+/- 8%) and NCC (50%+/- 11%), regardless of ECV status or calciuresis. Immunohistochemistry revealed reduced TRPV5 (43%+/- 2%), calbindin-D28K (59%+/- 1%) and NCC (56%+/- 4%) abundance. Furthermore, during HCTZ treatment, the subset of tubules coexpressing NCC and calbindin-D28K was significantly reduced (43%+/- 5%) and a disturbed cellular localization of NCC was observed. CONCLUSION: These data suggest that ECV contraction is a critical determinant of the thiazide-induced hypocalciuria, which is accompanied by a decreased expression of Ca2+ transport proteins.
INTRODUCTION:Thiazide diuretics have the unique characteristic of increasing renal Na+ excretion, while decreasing Ca2+ excretion. However, the molecular mechanism responsible for this thiazide-induced hypocalciuria remains unclear. The present study investigates the effect of thiazides on the expression of the proteins involved in active Ca2+ transport as well as the role of extracellular volume (ECV) status. METHODS:Hydrochlorothiazide (HCTZ), 12 mg/24 hours, was administered during 7 days to Wistar rats by osmotic minipumps. In addition, ECV contraction was either prevented by Na+ repletion or induced by a low-salt diet. Expression levels of the proteins involved in active Ca2+ transport [i.e., epithelial Ca2+ channel (TRPV5/ECaC1), calbindin-D28K, Na+/Ca2+ exchanger (NCX1)], as well as the thiazide-sensitive Na+ Cl- cotransporter (NCC) were determined by real-time quantitative polymerase chain reaction (PCR) and semiquantitative immunohistochemistry. RESULTS:HCTZ significantly reduced urinary Ca2+ excretion (22%+/- 5% relative to controls). Hematocrit was significantly increased, confirming ECV contraction. In addition, Na+ depletion virtually abolished Ca2+ excretion (8%+/- 1%), while Na+ repletion during HCTZ treatment prevented both ECV contraction and hypocalciuria. HCTZ significantly decreased mRNA expression of TRPV5 (71%+/- 6%), calbindin-D28K (53%+/- 6%), NCX1 (51%+/- 8%) and NCC (50%+/- 11%), regardless of ECV status or calciuresis. Immunohistochemistry revealed reduced TRPV5 (43%+/- 2%), calbindin-D28K (59%+/- 1%) and NCC (56%+/- 4%) abundance. Furthermore, during HCTZ treatment, the subset of tubules coexpressing NCC and calbindin-D28K was significantly reduced (43%+/- 5%) and a disturbed cellular localization of NCC was observed. CONCLUSION: These data suggest that ECV contraction is a critical determinant of the thiazide-induced hypocalciuria, which is accompanied by a decreased expression of Ca2+ transport proteins.
Authors: Shaleka L Eley; Crystal M Allen; Cicely L Williams; Richard D Bukoski; Mildred A Pointer Journal: Am J Hypertens Date: 2008-05-01 Impact factor: 2.689
Authors: Hye Ryoun Jang; Jay Wook Lee; Sejoong Kim; Nam Ju Heo; Jeong Hwan Lee; Hyo Sang Kim; Ji Yong Jung; Yun Kyu Oh; Ki Young Na; Jin Suk Han; Kwon Wook Joo Journal: J Korean Med Sci Date: 2010-08-14 Impact factor: 2.153
Authors: Hye Ryoun Jang; Sejoong Kim; Nam Ju Heo; Jeong Hwan Lee; Hyo Sang Kim; Søren Nielsen; Un Sil Jeon; Yun Kyu Oh; Ki Young Na; Kwon Wook Joo; Jin Suk Han Journal: J Korean Med Sci Date: 2009-01-29 Impact factor: 2.153