The effect of various cholecalciferol-related substances on the biosynthesis of the cholecalciferol-dependent calcium-binding protein in the small intestine of the rachitic chick and its relation to rickets.

Rachitic chicks were injected with different dose-levels of cholecalciferol and several cholecalciferol-related substances, i.e., dihydrotachysterol 3, ergocalciferol, 5,6-transcholecalciferol and 25-hydroxycholecalciferol. The response to treatment was assayed by the amount of cholecalciferol-dependent calcium-binding protein produced in the mucosa of the small intestine. The biological activity of these substances in the healing of rickets in the rat was also estimated except for ergocalciferol. The relative potencies in stimulating calcium-binding protein production were: 25-hydroxycholecalciferol > cholecalciferol > 5,6-trans-cholecalciferol > ergocalciferol > dihydrotachysterol 3.