No short-term effects of 24,25-dihydroxycholecalciferol in healthy subjects

Seven healthy volunteers were given 25 micrograms of 24,25-DHCC for one week to study the effects on calcium and bone metabolism. Mean plasma 24,25-DHCC concentration increased from 2.2 +/- 1.7 micrograms/l to 10.8 +/- 6.1 micrograms/l (p less than 0.001). No significant change was seen in the fasting plasma concentrations of Ca, Ca++, PTH and alkaline phosphatase activity and in urinary excretion of calcium and hydroxyproline and in tubular reabsorption of phosphate. The area under the curve for plasma ionized calcium concentration and urinary excretion of calcium during a standard calcium infusion of 10 mg/kg of Ca in 2 h did not change by 24,25-DHCC. We conclude that in healthy subjects no effect of 24,25-DHCC on the steady state parameters of calcium and bone metabolism, on renal calcium handling and on the handling of an intravenous calcium challenge by the homeostatic system could be demonstrated.