E. Fuku et al., IN-VITRO VIABILITY AND ULTRASTRUCTURAL-CHANGES IN BOVINE OOCYTES TREATED WITH A VITRIFICATION SOLUTION, Molecular reproduction and development, 40(2), 1995, pp. 177-185
Abattoir-derived oocytes were exposed to a concentrated cryoprotectant
solution (DAP213: 2 M DMSO, 1 M acetamide, 3 M propanediol, and 10% F
CS in TCM199) for 1.5 or 5 min at the germinal vesicle (GV) stage or a
fter maturation in vitro (IVM). Their viability was assessed by in vit
ro fertilization (IVF) and culture (IVC) to blastocysts. To investigat
e the effect of DAP213 on the ultrastructure, GV and IVM oocytes were
processed for transmission electron microscopy ITEM) before (control)
or after exposure to the cryoprotectant. DAP213 induced profound ultra
structural modifications to the microvilli and mitochondria, resulted
in large vesicle formation, and, most significantly, caused the premat
ure release of the cortical granules (CG). In IVM oocytes exposed to t
he cryoprotectant for 5 min, exocytosis of CG into the perivitelline s
pace was common and the IVF rate was reduced (P <.05). After exposure
for 5 min, GV oocytes displayed clusters of CG comparable to controls,
but after IVM-IVF, polyspermy rate was increased (P <.05). Furthermor
e, treated GV oocytes showed a reduced rate of cleavage and blastocyst
formation and an increased percentage of oocytes exhibiting alteratio
ns in organelles, whereas the viability and ultrastructure of IVM oocy
tes treated for 1.5 min was not different from controls. These observa
tions demonstrate that 1) cortical granule kinetics is one of the key
elements controlling fertilizability of bovine oocytes treated with cr
yoprotectant, and 2) GV oocytes are more sensitive to the cryoprotecta
nt than those that have already been matured in vitro, (C) 1995 Wiley-
Liss, Inc.