- Sterol(s) formed by ultraviolet irradiation of any 5,7-diene-3β-sterol, which breaks the 9,10 bond, but usually from either or both of ergosterol and lumisterol to produce t.2 (ertacalciol, (6E,22E)-9,10-secoergosta-5(10),6,8,22-tetraen-3β-ol) and from 7-dehydrocholesterol to produce t.3 (tacalciol, (6E,3S)-9,10-secocholesta-5(10),6,8-trien-3β-ol). When reduced to the 5,7-diene (or 5,7,22-triene) form, dihydrotachysterol3 (10,19-dihydrocalciol) or dihydrotachysterol2 (10,19-dihydroercalciol), antirachitic action appears. This property has been of therapeutic interest, but t. is being replaced by the true vitamin D hormone (calcitriol) and its derivatives.
* * *ta·chys·ter·ol ta-'kist-ə-.rȯl, -.rōl n an oily liquid alcohol C28H43OH isomeric with ergosterol that is formed by ultraviolet irradiation of ergosterol or lumisterol and that on further irradiation yields vitamin D2 see DIHYDROTACHYSTEROL
* * *tach·ys·te·rol (tak-isґtə-rol) an isomer of ergosterol produced by irradiation.
Medical dictionary. 2011.