Actinomycin D Inhibition of Vitamin D Action.

Injection of actinomycin D into rats completely prevents both the rise in serum calcium normally induced by vitamin D and the increased transport of calcium by everted intestinal sacs. Injection of excess parathyroid hormone did not alter this result; this eliminates the possibility that the inhibition of vitamin action was due to blocked hormone synthesis. As a result of these findings, a hypothesis concerning the mechanism of action of vitamin D is presented.