Stathmokinetic analysis of granulosa cell proliferation in antral follicles of cyclic rats.
On Day 1 of the estrous cycle (estrus), most of the largest follicles in the ovaries of rats appear to be healthy. By the following day, however, nearly one-third of all antral follicles show clear signs of atresia. The remaining healthy follicles are presumably those which will go on to ovulate. The object of this study was to distinguish between two possibilities: 1) that all of the largest follicles in the ovary on Day 1 subsequently undergo atresia on Day 2, and a new cohort of healthy follicles arises to replace them, or 2) that one single cohort of follicles on Day 1 is the source of both the healthy and atretic follicles seen on Day 2. For this purpose, the rate of granulosa cell proliferation was determined on each day of the 4-day estrous cycle using a metaphase arrest technique. Follicles grew most slowly on Day 4; small follicles (181-646 cells in the largest cross section) had a mitotic index (MI) of 8.1% after a 4-h block. In contrast, on Day 1 granulosa cells were proliferating rapidly; small follicles had an MI of 15.9%. This high rate of cell proliferation was also characteristic of large follicles. Estimated growth rates predict that, in healthy follicles, the number of granulosa cells should have almost doubled in the 24 h between Days 1 and 2. However, while the largest antral follicles in the ovaries on Day 1 had an average of 1064 cells in the largest cross section, the largest healthy follicles on Day 2 had only 1252 cells, rather than the expected 1763 cells.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D002452:Cell Count; D002455:Cell Division; D004971:Estrus; D005260:Female; D006107:Granulosa Cells / Q000166:cytology*; D007700:Kinetics; D008940:Mitotic Index; D006080:Ovarian Follicle / Q000502:physiology; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains