[Biological activity of 1alpha-hydroxycholecalciferol (1). Effect on intestine and bone in rats (author's transl)]

Biological activity of 1alpha-hydroxycholecalciferol was studied in rats. 1alpha-Hydroxycholecalciferol was found to be more potent and rapidly active than vitamin D in stimulating intestinal calcium transport and calcium mobilization from bone both in normal and vitamin D deficient rats. 1alpha-Hydroxycholecalciferol was also active in nephrectomized and/or thyroparathyroidectomized rats both in intestine and bone. Although it is well known that 1alpha-hydroxycholecalciferol is metabolized to 1alpha, 25-dihydroxycholecalciferol in the liver, there is the possibility that the former is active without further metabolism. In rats in which hepatitis was induced by CCl4, 1alpha-hydroxycholecalciferol was active both in the intestine and in the bone, while it was inactive in hepatectomized rats. These data clearly demonstrate that 1alpha-hydroxycholecalciferol is not active by itself and must be metabolized in the liver. This idea also shows the lag time in response of rats to 1alpha-hydroxycholecalciferol has more potent antirachitic activity than vitamin D and does not lose its activity with chronic oral administration. In view of these findings, 1alpha-hydroxycholecalciferol appears to have a good potential for clinical application in cases of renal failure and metabolic bone diseases.