Metabolism of Intravenously Administered Cholecalciferol in Man

Following intravenous injection of (3H) cholecalciferol into healthy subjects the disappearance of label from the plasma was followed by the reappearance ("rebound") of (3H) radioactivity associated exclusively with cholecalciferol. Lipoprotein fractionation of plasma revealed an increasing association of label with protein rather than lipoprotein during the rebound phase. We conclude that the rebound of plasma radioactivity reflects the transfer of label from lipoprotein to Vitamin D-binding globulin in the liver followed by its release into plasma.