title: Effect of urea during in vitro maturation on nuclear maturation and embryo development of bovine cumulus-oocyte-complexes.
abstract: High concentrations of urea in reproductive tract fluids are detrimental to bovine reproduction. Therefore, in experiment 1, the effect of 6 mM urea on nuclear maturation of cumulus-oocyte-complexes (COC) collected from abattoir ovaries was studied. After 4, 8, 12, 16, 20, and 24 h of in vitro maturation, the nuclear stages of samples of the COC were determined. During the first 8 h of maturation, germinal vesicle breakdown and chromosome condensation, resulting in the metaphase I stage, occurred at higher rates in the presence of urea. Segregation of the chromatids and extrusion of the polar body seemed to be impaired in the presence of urea, resulting in a higher percentage of oocytes arrested in metaphase I or telophase, and a lower percentage of oocytes in metaphase II after 24 h of maturation. Overall, nuclear progression of COC matured in the presence of urea differed from COC matured in control medium. In experiment 2, COC were matured for 24 h either in the presence or absence of 6 mM urea followed by in vitro fertilization and culture. After fertilization, a sample of the COC was fixed and stained to determine the fertilization rate. The cleavage rate was determined 3 d after start of maturation, and the stage of embryonic development was recorded 7 and 9 d after start of maturation. Based on cultured oocytes, urea in the maturation medium decreased the subsequent percentage of fertilization, cleavage, and development on d 7 and 9 (43.2, 56.1, 14.8, and 18.2%, respectively for urea vs. 64.1, 68.8, 22.4, and 23.9%, respectively for the control group). Embryonic development as a percentage of cleaved oocytes was not significantly affected by urea. Therefore, negative effects of urea were evident primarily during oocyte maturation and fertilization.
authors.affiliation: ID-Lelystad, The Netherlands. a.a.c.dewit@id.dlo.nl
authors.forename: A A
authors.initials: AA
authors.lastname: De Wit
authors.forename: M L
authors.initials: ML
authors.lastname: Cesar
authors.forename: T A
authors.initials: TA
authors.lastname: Kruip
mesh_terms: D000818:Animals; D002417:Cattle / Q000196:embryology*; D002455:Cell Division / Q000187:drug effects* / Q000502:physiology; D002467:Cell Nucleus / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques / Q000662:veterinary; D003470:Culture Media; D005260:Female; D005307:Fertilization in Vitro / Q000662:veterinary; D009865:Oocytes / Q000187:drug effects / Q000254:growth & development*; D013997:Time Factors; D014508:Urea / Q000494:pharmacology*
chemical_list: D003470:Culture Media; D014508:Urea