Actinomycin D Inhibition of Intestinal Transport of Calcium and of Vitamin D Action.

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Abstract
Summary Actinomycin D injection inhibits the actions of vitamin D in increasing concentrative transport of calcium across the intestinal wall in vitro and in raising serum calcium concentrations of fasted vitamin D-deficient rats. Actinomycin D blocks the transport of calcium across the mucosal surface of vitamin D-deficient as well as vitamin D-treated rats so that its action is on the calcium transport system rather than on the stimulatory effect of vitamin D. This inhibitory effect of actinomycin D on calcium transport is present within 3 hours of its subcutaneous injection and is less marked at 18 hours which suggests a direct interaction with the calcium transport system. Under the same conditions actinomycin D does not influence the transport of 1-tyrosine across the intestinal wall in vitro.