
the effect of actinomycin d on parathyroid-induced
change in bone and kidney.
actinomycin d (amd), an antibiotic known to
inhibit dna-directed rna synthesis,
was used to study parathyroid-induced changes
in ca mobilization in vivo and in vitro
as well as renal excretion of ca and phosphate
in rats.  intact and parathyroidectomized
rats subjected to peritoneal lavage were
administered amd, and changes in
ca, p, and mg in lavage and serum were
examined.  amd consistently lowered the
ca transfer into the peritoneal rinse in both
the intact and parathyroidectomized animals,
although the drop in ca was more acute
if the animals were pretreated by subcutaneous
injections of amd than if amd was
administered as a component of the
rinse.  pretreatment of lavaged animals with
amd prevented the expected increase
in osteoclast numbers in the distal metaphysis
of the femur but had no effect if administered
as a component of the peritoneal rinse.
the incubation of femora removed
from both intact and parathyroidectomized
animals resulted in media ca levels that
were significantly lower after 4 hr. incubation
when amd was added in vitro.  however,
transfer of recently injected ca into
the incubation medium from animals
treated with amd was increased.  in addition,
parathyroidectomy of animals subsequent
to administration of amd still resulted
in expected changes in ca and p in the
urine although amd significantly increased p
excretion in both intact and parathyroidectomized
animals.  it was concluded that
endogenous parathyroid hormone requires
the continuous production of enzymes ultimately
responsible for its action on bone
and kidney, but that this action is not necessarily
related directly to the production
of m-rna.
