The genotoxic effect of beta-propiolactone on mammalian oocytes.

beta-Propiolactone (beta PL) has been tested on preimplantation mouse embryos for possible genotoxic effects. Tests were performed at different stages of meiosis (late prophase I, diakinesis/metaphase I, anaphase I, telophase I/prophase II and metaphase II) by injecting females at various times after the induction of superovulation. Male and female derived chromosome complements from first-cleavage embryos were analysed before syngamy for cytogenetic abnormalities. A higher proportion of diploid oocytes, produced by the non-extrusion of the first or second polar body, was found after fertilization when the compound was administered immediately before metaphase I or II. No obvious effect was detected at any other time of beta PL exposure. Based on these results, several possible modes of action for beta PL are postulated.