A comparison of the effects of dietary calcium and phosphorus deficiency on the in vitro and in vivo metabolism of 25-hydroxycholecalciferol in the chick.
1. Young chicks fed a diet deficient in calcium showed an eightfold increase in the in vitro renal production of 1,25-dihydroxycholecalciferol (1,25-DHCC) and those fed a diet deficient in phosphorus showed a threefold increase when compared to chicks on a normal diet. 2. The in vivo accumulation of 1,25-DHCC in the gut mucosa was doubled in both low-Ca and low-P groups as was the rate of Ca absorption from the duodenum and the Ca-binding protein activity. The accumulation of 1,25-DHCC in bone increased threefold in the low-Ca group but showed no change in the low-P group. 3. It was concluded that the increased rate of Ca absorption found in dietary P deficiency depends rather upon the capacity of the gut mucosa to accumulate larger amounts of 1,25-DHCC than upon an increased renal production of this metabolite. The mechanism by which this is achieved is unknown, but it unlikely to be a general increase in availability of 1,25-DHCC since no rise occurred in bone 1,25-DHCC levels.
D000818:Animals; D002118:Calcium / Q000172:deficiency*; D002136:Calcium, Dietary / Q000378:metabolism; D002645:Chickens; D006887:Hydroxycholecalciferols / Q000378:metabolism*; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D008297:Male; D010758:Phosphorus / Q000172:deficiency*; D011485:Protein Binding
D002136:Calcium, Dietary; D006887:Hydroxycholecalciferols; D010758:Phosphorus; D002118:Calcium