Ovaries from adult cycling rats were studied from 1600 h on the
day
of prooestrus to 0700 h on the day of
oestrus in order to relate the cyclic hormonal changes to the proliferative
activity of preovulatory and
postovulatory (i.e. newly-formed corpora lutea) follicles. Proliferative
activity was studied by the
immunohistochemical demonstration of DNA-incorporated 5-bromodeoxyuridine
(BrdU). The proliferative
activity of granulosa cells (GC) in large preovulatory follicles showed
a
centripetal pattern and decreased
during prooestrus, reaching a minimum at 2100 h. However, a proliferative
wave
was found in the GC of
preovulatory follicles at 0200 h on the day of oestrus and in those of
newly-formed corpora lutea at 0700 h
on the day of oestrus. These results suggest that the granulosa cells of
preovulatory follicles show
maturational changes that followed a different pattern, depending on their
location within the follicle, and
that the proliferative wave found from 0200 to 0700 h on oestrus is important
for the establishment of the
number of steroidogenic cells in the cyclic corpus luteum.