
age differences in cellular
proliferation in rat kidneys
the hyperplastic response to unilateral ne-
phrectomy after 48 hours in the cortex and
medulla of the remaining kidneys of weanling
and young adult rats was studied by means of
autoradiography.  tritiated-thymidine, which
is destined exclusively for nucleoprotein synthe-
sis, was administered to 11 control and 11 ex-
perimental rats 4 hours prior to sacrifice.
labeled tubular cells were rare in control
tissues, especially in medulla, where the per-
centages did not differ greatly for the two age
groups.  in the cortex of controls such cells were
three times more frequent for weanling rats
than for adults.  significant increases in per-
centages of labeled cells over control levels
were found in both regions of the remaining
kidneys for both age groups.  the percentage of
increase was greater in medulla than in cortex
and most pronounced in medulla of the young
adult rats.
