Ovum Factor: A First Signal of Pregnancy?

Abstract

Previous studies have shown that, in the mouse, a factor is produced by the fertilized ovum within 24 h of mating. It cooperates with prolactin to stimulate ovarian production of component B or early pregnancy factor (EPF). This paper presents an initial characterization of the substance, termed ovum factor (OF). An indirect assay based on the rosette inhibition test for EPF has shown that OF is first released upon penetration of the ovum by the fertilizing spermatozoon. OF continues to be produced at least until blastulation. Processes which parthenogenetically activate the ovum are also capable of stimulating OF release from unfertilized ova. Gel filtration studies reveal that OF exists in multiple MW forms of approximately 160,000; 2,800; and 1,500. A substance with these characteristics has not been described previously; it may represent the first embryonic signal to the mother.

Early Pregnancy Factor (EPF): A Link between Fertilization and Immunomodulation

“…However, a specific stimulus is needed, e.g. spermatozoa, hyaluronoglucuronidase or Ca2+-and Mg2+-free medium, because ovum factor is not released from the cells either by diffusion or after sonic disruption (Cavanagh et al 1982) The results demonstrate the presence of EPF-A in serum. EPF-B was prepared by incubation of dioestrous mouse ovaries with ovum factor and prolactin as described by Cavanagh et al (1982).…”

“…unpublished data), pig and sheep ova (H. Morton, unpublished data), as well as mouse ova (Cavanagh et al 1982), have all been found to produce ovum factor, which is not species-specific in its biological activity; ovum factor produced from cultured human or pig embryos acts in the mouse similarly to mouse ovum factor. Furthermore, Nancarrow et al (1981) have shown that, after an infusion of mouse ovum factor, EPF can be detected in the serum of oestrous sheep.…”

“…Maternal ('early') EPF is produced during the pre-and peri-implantation periods while production offetal (,late') EPF begins in the peri-implantation stage and persists until at least mid-term. Maternal EPF consists of two components, EPF-A and EPF-B Morton et al 1980;Cavanagh et al 1982). EPF-A is oestrus-dependent and its presence in precursor form has been demonstrated in serum around the time of ovulation in mice , humans (B. E. Rolfe, personal communication), sheep (H. Morton, unpublished data) and pigs .…”

“…Morton et al (1980) and Cavanagh et al (1982) have shown that medium from fertilized mouse ova cultured in vitro does not have any detectable EPF at least until ova develop to the blastocyst stage; from this stage the production of fetal EPF from the embryo commences. Nancarrowet al (1981) similarly showed that infusates prepared from fertilized mouse ova did not contain EPF activity.…”

“…During the preimplantation stage of pregnancy EPF is produced by maternal tissue in response to a signal from the conceptus, and its continuing presence is directly related to the presence of a fertilized ovum Cavanagh et al 1982). Production in this manner continues until shortly after implantation, by which time embryonic tissue has commenced production of EPF (Morton et al 1982a).…”