An in vivo Analysis of Factors Influencing the Fertilization of Hamster Eggs

Abstract

Most current analytical studies of rodent fertilization are conducted in vitro because the environment can be manipulated and because of the small dimensions of the murine and cricetine oviduct. A technique was devised in which oocytes are instilled into the oviducts of mated hamsters, thereby allowing the investigation of some aspects of fertilization in vivo. Using this approach in intact or unilaterally ovariectomized females and, in some cases, with labeled oocytes to distinguish experimental from native ova, neither follicular fluid, cumulus oophorus nor corona radiata were required for fertilization in vivo. A demonstrated beneficial effect of these products on fertilization rate was not specific since maximal fertilization of cell free ova occurred when only homologous serum was used as their vehicle. Contrary to conclusions derived from recent in vitro studies, hamster diplotene oocytes are readily penetrable in vivo. The low rate of polyspermy in cell free ova transferred in serum denies the idea that the cumulus oophorus acts to protect against polyspermy by virtue of its physical presence. The high (23%) incidence in cell free ova transferred similarly, but in protein free medium suggests that it is the state of the ovum which determines the efficiency of the block to polyspermy in vivo.