
actinomycin d inhibition of intestinal transport of calcium and
of vitamin d action.
   actinomycin d injection inhibits the actions of vit d
in increasing concentrative transport of ca across the
intestinal wall in vitro and in raising serum ca concentrations
of fasted vit d-deficient rats.  actinomycin d blocks
the transport of ca across the mucosal surface of vit d
deficient as well as vit d-treated rats so that its action is
on the ca transport system, rather than on the stimulatory
effect of vit d.  this inhibitory effect of actinomycin d on
ca transport is present within 3 hr of its s. c. injection
and is less marked at 18 hr which suggests a direct interaction
with the ca transport system.  under the same conditions
actinomycin d does not influence the transport of
1-tyrosine across the intestinal wall in vitro.
