The mucified cumulus oophorus represents an outer enveloping layer around ovulated mammalian oocytes. This coat in its definitive expanded form appears late in the preovulatory development as a result of intensive secretion of intercellular matrix by cumulus cells. We have shown recently that antibodies to the cumulus matrix inhibit human fertilization in vitro. This study was undertaken to assess, in an animal model, the effects of anticumulus oophorus antibodies on fertility by use of different passive immunization protocols. A purified anticumulus immunoglobulin fraction was prepared from hyperimmune rabbit serum and administered at different times before and after mating to mice superovulated with equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). A dose-dependent negative effect of this anticumulus antibody preparation on the number of fertilized eggs recovered from the oviducts of treated animals was observed when the antibodies were given before mating. High antibody doses also interfered with oocyte maturation and ovulation if applied on the day of eCG treatment, but no effects on these processes were found when the antibodies were given on the day of hCG treatment. The antifertility effect of anticumulus antibodies was reversible and the antibodies did not affect postfertilization development. These findings make cumulus oophorus antigens serious candidates for the development of a contraceptive vaccine.

The nature of oocyte cytoplasmic factors controlling the development of the male pronucleus was investigated by inseminating human, zona-free oocytes at metaphase of the 1st and 2nd meiotic division. Oocytes at metaphase of the 2nd meiotic division could support the full structural and functional development of male pronuclei, whereas the vast majority of those at metaphase of the 1st meiotic division failed to do so. This suggests that oocyte cytoplasmic factors required for male pronuclear formation do not develop fully until the oocyte reaches the 2nd meiotic metaphase. When increasing numbers of spermatozoa entered one oocyte, the transformation of sperm nuclei into pronuclei was impaired progressively. The later stages of pronuclear development were particularly sensitive to polyspermy. These factors should be taken into consideration in the development of techniques of micromanipulation-assisted insemination.

This study was undertaken to determine the site of the acrosome reaction of spermatozoa penetrating into freshly inseminated human oocytes. The inseminated oocytes were treated with an anti-acrosin monoclonal antibody and the bound antibody was visualized at the ultrastructural level with the use of a second peroxidase-conjugated antibody. Quantitative analysis of serial thin sections cut throughout the specimens showed that the number of spermatozoa within the zona pellucida (potentially fertilizing ones) corresponded to the number of acrosin deposits associated with acrosomal ghosts on the zona pellucida surface. As it is known that a large acrosin bundle is liberated from a spermatozoon at a well-defined point of the acrosome reaction, these findings indicate that the acrosome reaction of the fertilizing spermatozoon must be exactly synchronized with its penetration through the egg vestments, apparently by the action of specific acrosome reaction-promoting substances in the oocyte/cumulus complex. These results represent a theoretical basis for evaluation of direct and indirect laboratory tests for human sperm acrosome reaction. 'Good' sperm samples should display elevated levels of acrosome-reacted spermatozoa after the administration of an appropriate stimulus and low levels of spontaneous acrosome reactions.