title: Ultrastructure of human mature oocytes after slow cooling cryopreservation with ethylene glycol.
abstract: The morphological characteristics of frozen-thawed human mature oocytes (n = 12) were studied by light and transmission electron microscopy following cryopreservation using a slow cooling protocol including increasing concentrations of ethylene glycol (0.5-1.5 mol/l) and sucrose 0.2 mol/l in the freezing solution. Fresh human mature oocytes (n = 12) were used as controls. Fresh and frozen-thawed oocytes appeared rounded in section, with a homogeneous cytoplasm, an intact oolemma and a continuous zona pellucida. Disorganization of mitochondria-smooth endoplasmic reticulum aggregates and a decreased complement of microvilli and cortical granules were frequently observable in frozen-thawed oocytes. Increased density of the inner zona pellucida, possibly related to the occurrence of zona 'hardening', was sometimes found associated with a reduced amount of cortical granules. In addition, delamination of the zona pellucida was evident in some frozen-thawed samples. Finally, numerous vacuoles and secondary lysosomes were detected in the ooplasm of most frozen-thawed oocytes. In conclusion, frozen-thawed oocytes treated with ethylene glycol may show a variety of ultrastructural alterations, possibly related, at least in part, to the use of this cryoprotectant. Thus, the ethylene glycol-based protocol of slow cooling herein described does not seem to offer significant advantages in terms of oocyte structural preservation.
authors.affiliation: Department of Anatomy, Sapienza University, Rome 00161, Italy. stefania.nottola@uniroma1.it
authors.forename: S A
authors.initials: SA
authors.lastname: Nottola
authors.forename: G
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authors.lastname: Coticchio
authors.forename: L
authors.initials: L
authors.lastname: De Santis
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authors.lastname: Macchiarelli
authors.forename: M
authors.initials: M
authors.lastname: Maione
authors.forename: S
authors.initials: S
authors.lastname: Bianchi
authors.forename: M
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authors.lastname: Iaccarino
authors.forename: C
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authors.lastname: Flamigni
authors.forename: A
authors.initials: A
authors.lastname: Borini