Factor(s) in Porcine Follicular Fluid Arresting the Induction of Cumulus Expansion of Oocyte-Cumulus Complexes Cultured In Vitro.

Oocyte-cumulus complexes cultured in porcine follicular fluid exhibited a significant expansion of the cumulus oophorus. Porcine follicular fluid was fractionated by ultracentrifugation (220, 000 × g for 48 h) and resulted in four fractions named as Top, Second, Third and Bottom. Cumulus-oocyte complexes cultured in Top fraction showed a more marked degree of expansion than did other fractions. When the activity of Top fraction was compared with that of the original porcine follicular fluid, there was much more activity for cumulus expansion caused by Top fraction. When Bottom fraction was mixed with Top fraction, there was a significant decrease in the degree of expansion of the cumulus oophorus in vitro. In the same manner, when oocytectomized complexes were cultured in Top + Bottom fraction, the expansion activity of Top fraction was also suppressed. The arresting action can be altered when re-cultured in Top fraction, suggesting that it has a reversible action on cumulus expansion. The arresting activity was retained after dialysis in a tubing with a molecular cut off of 50 kDa.