Histological evidence for heterogeneity in the development of preovulatory pig follicles

Ovaries were collected from naturally cycling gilts during the preovulatory period and the stage relative to the LH surge estimated by measurement of oestradiol and progesterone concentrations in follicular fluid. Many of the follicles recovered had become flaccid with an associated increase in follicular fluid viscosity. Marked infolding of both the granulosa and theca tissue in some follicles suggested early luteinization. However, these morphological changes did not necessarily occur simultaneously in the same follicle, or in all follicles within an ovary. Moreover, they were not consistently related to characteristic differences in the concentration of follicular fluid steroids, suggesting either that the morphological and biochemical aspects of the luteinization of follicles may be independently controlled, or may respond at different rates to the same signal.