Videotape analysis of hamster ovulation in vitro.

Videotape recordings were made of hamster follicles ovulating in vitro. These recordings were analyzed to characterize the morphological changes occurring in ovulating follicles and to time various events in the ovulation sequence. Before rupture, the shape of the follicle is transformed from a low to tall profile as shown previously (Martin and Talbot, '81). The complete transition from a low to tall profile required about 22.5 min. During the profile transition, the smooth muscle cells (SMC) in the base of the follicle contract (Martin and Talbot, '81), and the following events were observed. The base of the follicle moved apically. This pressed the cumulus and oocyte against the apical follicle wall, which appeared granular rather than smooth. The size of the antrum decreased presumably due to obliteration of the basal part of the antrum and movement of follicular fluid through the developing rupture site in the apex. The pressing of the cumulus against the apical wall appeared to cause final thinning and opening of the rupture site. The cumulus was extruded in two phases. Phase 1 was rapid (10-60 sec) and resulted in evacuation of about 25% of the cumulus and usually the oocyte from the antrum. Phase 2 required 2-10 min for completion and was accompanied by collapse of the follicle wall. After collapse, the cumulus remained with its follicle and could not be removed by pulling with Watchmaker's forceps. These observations provide new information on the role of SMC in hamster ovulation and characterize extrusion of the cumulus as a two-phase event.