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Zona pellucida solubility and cortical granule complements in human oocytes following assisted reproductive techniques

Published online by Cambridge University Press:  06 August 2001

C. Manna
Affiliation:
Genesis, Centro per la Riproduzione Umana e Terapia dell'Infertilità, Rome, Italy.
L. Rienzi
Affiliation:
Centro di Reproduzione Umana, European Hospital, Rome, Italy.
E. Greco
Affiliation:
Centro di Reproduzione Umana, European Hospital, Rome, Italy.
M. Sbracia
Affiliation:
Centro di Endocrinologia e Medicina della Riproduzione, Rome, Italy.
A. Rahman
Affiliation:
Genesis, Centro per la Riproduzione Umana e Terapia dell'Infertilità, Rome, Italy.
R. Poverini
Affiliation:
Centro di Reproduzione Umana, European Hospital, Rome, Italy.
G. Siracusa
Affiliation:
Sezione di Istologia e Embriologia, Dipartimento di Sanità Pubblica e Biologia Cellulare, Università de Roma ‘Tor Vergata’, Rome, Italy.
M. De Felici
Affiliation:
Sezione di Istologia e Embriologia, Dipartimento di Sanità Pubblica e Biologia Cellulare, Università de Roma ‘Tor Vergata’, Rome, Italy.

Abstract

In this study the solubility to α-chymotrypsin of the zona pellucida (ZP) of human oocytes and polyploid embryos obtained during various clinical procedures of assisted fertilisation (IVF, ICSI, cyropreservation) was evaluated. The aim of the study was to determine whether changes in ZP solubility occur during such procedures and whether abnormal solubility could be likened to fertilisation failure. Correlation between ZP solubility and cortical granule (CG) density was also studied. The results showed that ZP solubility varied considerably among germinal vesicle or metaphase oocytes obtained from different subjects, but was essentially identical for the oocyte cohort obtained from individual women. On the basis of ZP solubility metaphase oocytes were subdivided into two classes: class I, average ZP dissolution time ± SE = 24.1 ± 0.9 min, n = 28; and class II, 46.7 ± 2.0 min, n = 13. Prolonged ZP dissolution times of metaphase oocytes were significantly correlated with a low in vitro fertilisation rate in sibling oocytes. The zonae of fertilised eggs (polyploid embryos) showed long solubilisation times (IVF: 45.3 ± 3.4 min, n = 18; ICSI: 48.9 ± 2.7 min, n = 19). ZP solubility of oocytes that failed to fertilise was intermediate between that of class I metaphase oocytes and embryos (unfertilised IVF: 33.0 ± 2.7 min, n = 13; unfertilised ICSI: 43.0 ± 2.4 min, n = 9). A moderate spontaneous ZP hardening occurred when metaphase oocytes were cultured for 24 h. Finally, cryopreservation of unfertilised oocytes caused hardening of their ZP, with dissolution times that were comparable to those found in fertilised eggs (49.5 ± 2.3 min, n = 10). In most cases, an inverse correlation was found between ZP dissolution time and CG density (longer solubilisation times corresponding to lower CG density). ZP hardening caused by cryopreservation, however, was not associated with a significant reduction in CG density in most of the oocytes examined.

Type
Research Article
Copyright
© 2001 Cambridge University Press

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