Calcitriol-d6 is intended for use as an internal standard for the quantification of calcitriol by GC- or LC-MS. Calcitriol is a vitamin D3 receptor agonist and an active metabolite of vitamin D3 .1,2 It is formed via a multi-step process, in which vitamin D3 undergoes hydroxylation to 25-hydroxy vitamin D3 in the liver, followed by further hydroxylation at the 1α-position in the kidney. Calcitriol binds to the vitamin D3 receptor (Kd = 16 pM) and induces differentiation of U937 acute monocytic leukemia cells (EC50 = 2,000 pM).3 It induces cell cycle arrest at the S phase and apoptosis in primary adenomatous and hyperplastic human parathyroid cells when used at a concentration of 10 nM.4 Calcitriol (0.65 nmol/animal) increases bone calcium mobilization in chicks on a low-calcium diet.2 It stimulates calcium absorption in the intestines in a chick model of rickets induced by a vitamin D3-deficient diet when administered at a dose of 25 ?g/animal.1 Formulations containing calcitriol have been used in the treatment of hypocalcemia.
1.Lawson, D.E., Fraser, D.R., Kodicek, E., et al.Identification of 1,25-dihydroxycholecalciferol, a new kidney hormone controlling calcium metabolismNature230(5291)228-230(1971) 2.Haussler, M.R., Zerwekh, J.E., Hesse, R.H., et al.Biological activity of 1α-hydroxycholecalciferol, a synthetic analog of the hormonal form of vitamin D3Proc. Natl. Acad. Sci. USA70(8)2248-2252(1973) 3.Binderup, L., Latini, S., Binderup, E., et al.20-epi-vitamin D3 analogues: A novel class of potent regulators of cell growth and immune responsesBiochem. Pharmacol.42(8)1569-1575(1991) 4.Canalejo, A., Almadén, Y., Torregrosa, V., et al.The in vitro effect of calcitriol on parathyroid cell proliferation and apoptosisJ. Am. Soc. Nephrol.11(10)1865-1872(2000)