Follicular Development and Ovulation in Macrophage Colony-Stimulating Factor-Deficient Mice Homozygous for the Osteopetrosis (Op) Mutation1

To clarify the role of macrophages and macrophage colony-stimulating factor (M-CSF) in follicular development and ovulation, the processes of folliculogenesis and ovulation, numerical changes in macrophages, and proliferative capacity of granulosa cells were examined in op/op mice before or after daily M-CSF administration. The natural estrous cycle was determined daily by means of vaginal smears. The number of ovulated ova in both fallopian tubes was significantly smaller in op/op mice than in normal littermates. Such ova markedly increased in number after daily M-CSF administration. The numbers of both antral and mature follicles in the proestrous ovary were markedly lower in op/op mice than in the controls and increased after daily M-CSF administration. Flash-labeling with [3H]thymidine showed that the proliferative capacity of granulosa cells in antral follicles was reduced in op/op mice but elevated after daily M-CSF administration. Numbers of granulosa cells and macrophages in the antral follicles were significantly decreased in op/op mice but were increased after M-CSF treatment. All these data provide evidence that macrophages are implicated in the process of folliculogenesis and ovulation.