Decreased mRNA expression of the PTH/PTHrP receptor and type II sodium-dependent phosphate transporter in the kidney of rats fed a high phosphorus diet accompanied with a decrease in serum calcium concentration.
This study investigates the phosphorus (P) homeostasis in the process of an altered parathyroid hormone (PTH) action in the kidney of rats fed a high P diet. Four-week-old male Wistar strain rats were fed diets containing five different P levels (0.3, 0.6, 0.9, 1.2 and 1.5%) for 21 days. The serum PTH concentration and urinary excretion of P were elevated with increasing dietary P level. Compared to rats fed the 0.3% P diet, the serum calcium (Ca) concentration remained unchanged, while the serum 1,25(OH)(2)D(3) concentration and urinary excretion of cAMP were elevated with increasing dietary P level in rats fed the high P diets containing 0.6-0.9% P. On the other hand, a lower serum Ca concentration was observed in rats fed the high P diets containing 1.2% or greater P. The serum 1,25(OH)(2)D(3) concentration remained unchanged in rats fed the high P diets containing 1.2% or greater P, comparison with rats fed the 0.3% P diet. The urinary excretion of cAMP and PTH/PTH-related peptide (PTHrP) receptor and type II sodium-dependent phosphate transporter (NaPi-2) mRNA in the kidney were both decreased in rats fed the high P diets containing 1.2% or greater P. In conclusion, a high P diet with subsequent decrease in serum Ca concentration suppressed the PTH action in the kidney due to PTH/PTHrP receptor mRNA down-regulation. Furthermore, an increase in the urinary excretion of P might have been caused by decreased NaPi-2 mRNA expression without the effects of PTH and 1,25(OH)(2)D(3).
Katsumata
Shin-ichi
S
Department of Nutritional Science, Faculty of Applied Bioscience, Tokyo University of Agriculture, 1-1-1 Sakuragaoka, Setagaya-ku, Tokyo 156-8502, Japan.
Masuyama
Ritsuko
R
Uehara
Mariko
M
Suzuki
Kazuharu
K
D000818:Animals; D002118:Calcium / Q000097:blood*; D000242:Cyclic AMP / Q000652:urine; D004032:Diet; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D006706:Homeostasis; D007668:Kidney / Q000378:metabolism*; D008297:Male; D010281:Parathyroid Hormone / Q000502:physiology; D010758:Phosphorus / Q000008:administration & dosage*; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017208:Rats, Wistar; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000235:genetics*; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters / Q000235:genetics*
D010281:Parathyroid Hormone; D012333:RNA, Messenger; D044168:Receptor, Parathyroid Hormone, Type 1; D050608:Sodium-Phosphate Cotransporter Proteins; D050610:Sodium-Phosphate Cotransporter Proteins, Type II; D027981:Symporters; D010758:Phosphorus; D000242:Cyclic AMP; D002118:Calcium