Calcimimetic compound upregulates decreased calcium-sensing receptor expression level in parathyroid glands of rats with chronic renal insufficiency.
The reduced expression level of the calcium-sensing receptor (CaR) is attributed to the hyposensitivity of parathyroid cells to extracellular calcium concentration [Ca2+]o, which plays a crucial role in the pathogenesis of secondary hyperparathyroidism (SHPT) in patients and rats with chronic renal insufficiency (CRI). Calcimimetic compounds have been demonstrated to improve the decreased sensitivity of CaR to extracellular calcium concentration and to suppress both parathyroid hormone (PTH) oversecretion and parathyroid cell proliferation. However, the effect of calcimimetics on the reduced CaR expression level in parathyroid cells in CRI remains unclarified. The aim of this investigation was to examine the effect of the calcimimetic compound NSP R-568 (R-568) on the CaR expression in the parathyroid cells of rats with experimental CRI. Subtotally nephrectomized rats were fed a high-phosphorus diet for 8 (n = 12; Nx-8 group) or 9 wk (n = 11; Nx-9 group) to induce severe SHPT. Another group of uremic rats were fed a high-phosphorus diet for 8 wk and then orally administered R-568 (100 micromol/kg body wt) once a day for 7 d (n = 11; Nx+R-568 group). Sham-operated rats that were fed a standard diet for 9 wk were used as controls (n = 8). R-568 treatment induced a significant reduction in plasma PTH level with significant decrease in serum calcium and without change in serum phosphorus concentration. Serum 1,25(OH)2D3 level was not affected by R-568 administration. CaR mRNA and protein levels in the Nx-8 and Nx-9 groups significantly decreased compared with those in the controls; however, no significant difference in these parameters was observed between the Nx-8 and Nx-9 groups. In the Nx+R-568 group, CaR mRNA and protein levels significantly increased compared with those in either the Nx-8 or Nx-9 group. R-568 was effective in reducing the number of proliferating cell nuclear antigen-positive cells along with parathyroid gland growth suppression in the Nx+R-568 group compared with that in the Nx-9 group. The results suggest that the calcimimetic compound R-568 upregulates decreased CaR expression, and the upregulation possibly has an enhancement effect on PTH secretion and parathyroid cell hyperplasia through the improved sensitivity of CaR to [Ca2+]o.
Center for Blood Purification Therapy, Wakayama Medical University, Japan. mizobu@wakayama-med.ac.jp
Masahide
M
Mizobuchi
Ikuji
I
Hatamura
Hiroaki
H
Ogata
Fumie
F
Saji
Susumu
S
Uda
Kazuhiro
K
Shiizaki
Toshifumi
T
Sakaguchi
Shigeo
S
Negi
Eriko
E
Kinugasa
Shozo
S
Koshikawa
Tadao
T
Akizawa
D000704:Analysis of Variance; D000814:Aniline Compounds / Q000494:pharmacology*; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000819:agonists*; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D007150:Immunohistochemistry; D007676:Kidney Failure, Chronic / Q000473:pathology*; D008297:Male; D008969:Molecular Sequence Data; D009392:Nephrectomy; D010280:Parathyroid Glands / Q000378:metabolism*; D010627:Phenethylamines; D011336:Probability; D011437:Propylamines; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D044169:Receptors, Calcium-Sensing / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D012016:Reference Values; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D015854:Up-Regulation
D000814:Aniline Compounds; C107873:N-(2-chlorophenylpropyl)-1-(3-methoxyphenyl)ethylamine; D010627:Phenethylamines; D011437:Propylamines; D044169:Receptors, Calcium-Sensing; D002118:Calcium