steroid hormone calciol A hydroxy seco-steroid that is (5Z,7E)-9,10-secocholesta-5,7,10(19)-triene in which the pro-S hydrogen at position 3 has been replaced by a hydroxy group. It is the inactive form of vitamin D3, being hydroxylated in the liver to calcidiol (25-hydroxyvitamin D3), which is then further hydroxylated in the kidney to give calcitriol (1,25-dihydroxyvitamin D3), the active hormone. A hydroxy seco-steroid that is (5<i>Z</i>,7<i>E</i>)-9,10-secocholesta-5,7,10(19)-triene in which the <em>pro</em>-<i>S</i> hydrogen at position 3 has been replaced by a hydroxy group. It is the inactive form of vitamin D<small>₃</small>, being hydroxylated in the liver to calcidiol (25-hydroxyvitamin D<small>₃</small>), which is then further hydroxylated in the kidney to give calcitriol (1,25-dihydroxyvitamin D<small>₃</small>), the active hormone. cholecalciferol secondary alcohol seco-cholestane D3 vitamins