The effect of dietary protein on the biological activity of cholecalciferol and its metabolites in the rachitic rat.

Rats maintained on low-protein rachitogenic diets show increased intestinal calcium transport, serum inorganic phosphate and increased endochondral calcification responses to calciferol, 25-hydroxycholecalciferol (25-OH-CC) and 1,25-dihydroxycholecalciferol (1,25-(OH)2CC). Because enhanced responses are observed with 1,25-dihydroxycholecalciferol as well as its precursors, it is unlikely that the effect of dietary protein is mediated by a change in the calciferol-25-hydroxylase and the 25-hydroxycholecalciferol-1 alpha-hydroxylase. Instead, it appears that either metabolism of 1,25-dihydroxycholecalciferol or its activity in the target organs is affected.