02-15-2011, 03:59 PM
no, it's D2 - 25 cholecalciferol, because liver 25-hydroxylase is not regulated, and whatever comes in, gets 25 hydroxilated. But when 1-hydroxylase converts too much to D3, there is a salvage pathway, that degrades 1, 25- cholecalciferol(D3) to inactive 24,25-cholecalciferol