Damaging effect of cumulus denudation on rabbit oocytes.

Objective: To study the effect of cumulus denudation on in vitro maturation of rabbit oocytes.

Design: Experimental animal study.

Setting: Academic institution.

Animal(s): Rabbits and mice.

Intervention(s): Rabbit oocytes were observed compared with mouse oocytes.

Main Outcome Measure(s): Developmental competence, membrane integrity, and apoptotic status of oocytes after cumulus denudation.

Result(s): Although in vitro maturation of mouse cumulus-denuded oocytes was unaffected, rabbit cumulus-denuded oocytes could not mature. However, 50% of rabbit cumulus-intact oocytes matured normally when their gap junctions were sealed with 1-heptanol. Coculture with cumulus cells did not improve maturation of rabbit cumulus-denuded oocytes unless with an intact corona radiata. Staining with Hoechst 33258, Bcl-2 antibodies, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling showed membrane breaches or apoptosis of rabbit cumulus-denuded oocytes, contrary to the mouse cumulus-denuded oocytes. Ultrastructurally, rabbit oocytes showed no perivitelline space but numerous long cell junctions projecting into the egg cortex, contrary to the mouse oocytes. However, the damaging effect of cumulus denudation was much relieved after preincubation of rabbit cumulus-intact oocytes with phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine, and some cumulus-denuded oocytes prepared after preincubation matured and developed into blastocysts.

Conclusion(s): [1] Cumulus denudation severely damaged rabbit oocytes leading to their apoptosis or degeneration, possibly because of the deep-set junctional complexes anchoring the oocyte and corona cells; and [2] preincubation with phosphodiesterase inhibitor may provide a method to avoid the damaging effect of cumulus denudation on rabbit oocytes.