The effects of pig follicular fluid upon the ultrastructure of rat granulosa cells in tissue culture

The ultrastructure of rat granulosa cells from preovulatory follicles has been investigated after incubation in control fetal calf serum (FCS) medium with or without LH (1 micron/ml), and in total or steroid-free pig follicular fluid (FF) medium. While the cells had a similar ultrastructure after 1 day of incubation in these media, significant differences were detectable after 3 days. In FCS supplemented with LH, autolysis and phagocytotic activity remained elevated, and cells did not develop any of the typical ultrastructural features of steroid-secreting cells. In contrast, total FF induced complete differentiation of mitochondrial cristae from the lamelliform to the villiform type. Steroid-free FF induced the same array of effects as total FF, except that mitochondrial differentiation was not complete. These observations together with those of previous studies, in which progesterone secretion was measured in cells incubated in the same media, suggested that the development of the capacity to secrete progesterone in rat luteal cells could be directly related only to mitochondrial differentiation.