The rat calcium-sensing receptor is regulated by vitamin d but not
by calcium.
Brown, A. J., M. Zhong, J. Finch, C. Ritter, R. McCracken, J.
Morrissey, and E. Slatopolsky.
Dept. of Medicine, Washington University, St. Louis, MO 63110
APStracts 2:0174F, 1995.
Parathyroid hormone secretion is regulated by extracellular calcium
acting through a cell surface calcium receptor (CaR). We have
examined the potential regulation of the CaR in the parathyroid
glands (PTG) and kidney by calcium and 1,25-dihydroxyvitamin D3
[1,25-(OH)2D3]. Rats fed vitamin D-deficient (-D) diets containing
0.02%, 0.4% or 2.0% Ca had a wide range of serum ionized Ca (ICa)
(2.5 to 5.2 mg/dl) and PTH (22 to 590 pg/ml). PTG CaR mRNA did not
vary significantly with ICa or PTH, indicating that hypocalcemia and
hyperparathyroidism may not alter CaR expression. However, PTG CaR
mRNA was 40% lower in the -D rats than in age-matched rats fed a
vitamin D-replete (+D) diet (p < 0.002). Repletion of -D rats
with 1,25-(OH)2D3 produced a dose-dependent increase in PTG CaR mRNA.
Treatment of +D rats with 100 ng of 1,25-(OH)2D3 increased CaR mRNA
by 33% (p < 0.05) and 54% (p < 0.002) in PTG and by 89% (p
< 0.02) and 91% (p < 0.02) in the kidney in two independent
experiments. PTG CaR peaked at 16 hours (150% of control, p <
0.05) following 1,25-(OH)2D3 administration but returned to normal by
24 hours. This up-regulation of CaR expression by 1,25-(OH)2D3 may be
involved in the suppressive effects of vitamin D compounds on PTH
secretion.
Received 22 May 1995; accepted in final form 18 September 1995.
APS Manuscript Number F161-5.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95