Biological activity of la-hydroxycholecalciferol(II). Effect on the metabolism of calcium and phosphorus in rats

Effect of 1alpha-hydroxycholecalciferol on the metabolism of calcium and phosphorus was studied using Ca-labelled and non-labelled rats. With an oral daily dose of 2.5 or 12.5 microgram/kg of 1alpha-hydroxycholecalciferol, serum calcium, urine volume, urinary calcium excretion, urinary calcium concentration and water consumption increased, while fecal concentration, urinary phosphorus concentration and food consumption decreased. There was a lag time (1 or 2 days) between the increase of serum calcium and that of specific activity of serum calcium, and bone resorption was stimulated later than was intestinal calcium transport. After 10 days treatment, calcium concentration in the femur decreased, while a remarkable calcification was noted in soft tissues such as kidney, intestine, aorta, heart and muscle, although these effects were reduced with lower doses of the drug. With a smaller oral daily dose (0.1 or 0.5 microgram/kg), for 6 months, bone calcium and phosphorus concentration increased without soft tissue calcification. Thus, 1alpha-hydroxycholecalciferol may be an effective drug for patients with metabolic bone diseases.