Fluoride Modulates Parathyroid Hormone Secretion In Vivo and In Vitro

Abstract

The study objective was to investigate fluoride’s effects on iPTH secretion. Thryo-parathyroid complexes (TPCs) from C3H (n=18) and B6 (n=18) mice were cultured in Ca2+ optimized medium. TPCs were treated with 0, 250 or 500µM NaF for 24hrs and secreted iPTH assayed by ELISA. C3H (n=78) and B6 (n=78) mice were gavaged once with distilled or with fluoride (0.001mg [F ⁻]/g body weight) water. At serial time points (0.5–96hrs) serum iPTH, fluoride, total calcium, phosphorus and magnesium levels were determined. Expression of genes involved in mineral regulation via bone-parathyroid-kidney (BPK) axis such as: Pth, Casr, Vdr, Pthlh, Fgf23, αKlotho, Fgf1rc, Tnfs11, Pth1r, Slc34a1, Slc9a3r1, Clcn5 and Pdzk1 were determined in TPCs, humerii and kidneys at 24hrs. An in vitro decrease in iPTH was seen in C3H and B6 TPC at 500µM ( p<0.001). In vivo levels of serum fluoride peaked at 0.5hr in both C3H ( p=0.002) and B6 ( p=0.01). In C3H, iPTH decreased at 24hrs ( p<0.0001) returning to baseline at 48hrs. In B6, iPTH increased at 12hrs ( p<0.001) returning to baseline at 24hrs. Serum total calcium, phosphorus and magnesium did not change significantly. Pth, Casr, αKlotho, Fgf1rc, Vdr and Pthlh were significantly up-regulated in C3H TPC as compared to B6. Conclusions, fluoride’s effects on TPC in vitro were equivalent between the two mouse strains. However, fluoride demonstrated an early strain dependent effect on iPTH secretion in vivo. Both strains demonstrated a differences in the expression of genes involved in BPK axis suggesting a possible role in physiologic handling of fluoride.