PROLIFERATIVE ACTIVITY OF PREOVULATORY FOLLICLES AND NEWLY FORMED CORPORA-LUTEA IN CYCLING RATS FROM LATE PROESTRUS TO EARLY ESTRUS

Ovaries from adult cycling rats were studied fr om 1600 h on the day o f prooestrus to 0700 h on the day of oestrus in order to relate the cy clic hormonal changes to the proliferative activity of preovulatory an d postovulatory (i.e. newly-formed corpora lutea.) follicles. Prolifer ative activity was studied by the immunohistochemical demonstration of DNA-incorporated 5-bromodeoxyuridine (BrdU). The proliferative activi ty of granulosa cells (GC) in large preovulatory follicles showed a ce ntripetal pattern and decreased during prooestrus, reaching a minimum at 2100 h. However, a proliferative wave was found in the GC of preovu latory 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 s uggest that the granulosa cells of preovulatory follicles show maturat ional changes that followed a different pattern, depending on their lo cation within the follicle, and that the proliferative wave found from 0200 to 0700 h on oestrus is important for the establishment of the n umber of steroidogenic cells in the cyclic corpus luteum.