Flow cytofluorometric analysis of granulosa cell proliferation in rats

Immature rats were given PMSG followed by an ovulatory dose of hCG. Mature cyclic rats were given an ovulatory dose of hCG on the day of dioestrus, 24 h before the endogenous LH surge was expected to occur. Granulosa cells from individual follicles were subjected to flow cytometry at various times after hormone administration. Administration of PMSG to immature rats caused a marked, transient increase in 'cycling' granulosa cells (cells in S, G2, or M phases of the cell cycle). Administration of hCG to adult cyclic rats caused a slight, but significant, increase in 'cycling' granulosa cells. The results could be taken to indicate that hCG-induced luteinization is not, in fact, accompanied by cessation of cellular proliferation. However, the data lend themselves to alternative explanations. The observed phase shifts may be due to the lengthening of the duration of S and G2 phases, indicating an actual decrease in the rate of cell proliferation. Flow cytometry was found to be a rapid, inexpensive tool for the study of follicular growth in the rat, but, due to variation between follicles and the need for a minimal sample size of 2000 cells, its application is limited to large follicles.