Calcitetrol(1α, 24, 25-Trihydroxy VD3) is the hormonally active form of vitamin D with three hydroxyl groups.IC50 value:Target: Calcitriol increases blood calcium levels ([Ca2+]) by promoting absorption of dietary calcium from the gastrointestinal tract and increasing renal tubular reabsorption of calcium, thus reducing the loss of calcium in the urine. Calcitriol also stimulates release of calcium from bone by its action on the specific type of bone cells referred to as osteoblasts, causing them to release RANKL, which in turn activates osteoclasts.
[1]. Johanna A. Huhtakangas, Christopher J. Olivera, June E. Bishop et al. The Vitamin D Receptor Is Present in Caveolae-Enriched Plasma Membranes and Binds 1α,25(OH)2-Vitamin D3in Vivo and in Vitro. Molecular Endocrinology November 1, 2004 vol. 18 no. 11 2660 [2]. Robert A. Parise, Merrill J. Egorin, Beatriz Kanterewicz et al. CYP24, the enzyme that catabolizes the antiproliferative agent vitamin D, is increased in lung cancer. International Journal of Cancer. Volume 119, Issue 8, pages 1819-1828, 15 October 2006 [3]. Akiyoshi-Shibata M, Sakaki T, Ohyama Y, Noshiro M, Okuda K, Yabusaki Y. Further oxidation of hydroxycalcidiol by calcidiol 24-hydroxylase. A study with the mature enzyme expressed in Escherichia coli. Eur J Biochem. 1994 Sep 1;224(2):335-43. [4]. Sonoko Masuda, Valarie Byford, Alice Arabian et al. Altered Pharmacokinetics of 1α,25-Dihydroxyvitamin D3 and 25-Hydroxyvitamin D3 in the Blood and Tissues of the 25-Hydroxyvitamin D-24-Hydroxylase (Cyp24a1) Null Mouse. Endocrinology February 1, 2005 vol.