Demonstration of the rapid action of pure crystalline 1 alpha-hydroxy vitamin D3 and 1 alpha,25-dihydroxy vitamin D3 on intestinal calcium uptake.

The biological effects of crystalline 1alpha-hydroxyvitamin D3 and crystalline 1alpha,25-dihydroxyvitamin D3 have been compared on the intestinal uptake of calcium-45 by everted duodenal gut sacs from rachitic rats. Peak calcium-45 uptake was observed 1 hr after intravenous administration and both crystalline vitamin D2 analogs were of comparable potency. The rapid onset of calcium-45 uptake and the rapid attainment of maximal calcium-45 transport suggests a direct effect of these crystalline analogs on the mucosal membranes of the intestinal cell.