title: Studies on zona hardening in rat oocytes that are matured in vitro in a serum-free medium.
abstract: The present study confirms that zona pellucidae of rat oocytes became resistant to chymotrypsin digestion (zona hardening) after undergoing in vitro maturation (IVM) in a serum-free medium. However, zona hardening did not occur when empty zonae without oocytes were cultured in the same IVM conditions, suggesting that oocyte-derived factor(s) is responsible for zona hardening in oocytes matured in the serum-free medium. Zona hardening occurred primarily after dictyate oocytes were cultured for 6-8 hours in the IVM medium without serum. Zona hardening could be prevented or alleviated if oocytes were cultured in the IVM medium containing bovine foetal calf serum, a soybean trypsin inhibitor, or beta-mercaptoethanol, and in vitro fertilization rates for such oocytes were normal. Possible mechanisms of the phenomenon of zona hardening in oocytes matured in serum-free conditions are discussed in relation to its possible relevance to the cortical reaction and the physiological block to polyspermy.
authors.affiliation: Department of Physiology, University of Western Ontario, London, Canada.
authors.forename: X
authors.initials: X
authors.lastname: Zhang
authors.forename: J
authors.initials: J
authors.lastname: Rutledge
authors.forename: D T
authors.initials: DT
authors.lastname: Armstrong
mesh_terms: D000818:Animals; D002918:Chymotrypsin / Q000378:metabolism; D003470:Culture Media; D046508:Culture Techniques; D005260:Female; D005307:Fertilization in Vitro; D007700:Kinetics; D008623:Mercaptoethanol / Q000494:pharmacology; D009865:Oocytes / Q000254:growth & development; D051381:Rats; D011919:Rats, Inbred Strains; D014361:Trypsin Inhibitors / Q000494:pharmacology; D015044:Zona Pellucida / Q000502:physiology*
chemical_list: D003470:Culture Media; D014361:Trypsin Inhibitors; D008623:Mercaptoethanol; D002918:Chymotrypsin