Somatic cell amplification of early pregnancy factors in the fallopian tube.

This essay is concerned with the function of ovarian somatic cells, especially those of the cumulus oophorus, that are shed with the oocyte at the time of ovulation. Once dissociated from the surface of the oocyte(s), they remain in its close vicinity or that of the zygote(s) throughout the tubal sojourn. Most such follicular cells are not moribund or dead but continue to be synthetically active, although showing ultrastructural modification. Their secretions may include steroid hormones, prostaglandins and diverse peptides, molecules that would be presented locally to the endosalpinx. The cell suspension represents a potential route of amplification of early pregnancy signals from the embryo to influence the pattern of ovarian steroid secretion and perhaps that of folliculogenesis. Bearing in mind the relatively low concentration of hormones generated by the somatic cell suspension, vascular counter-current transfer of information is postulated from the Fallopian tube to the ipsilateral ovary. Molecular techniques are being applied as a means of examining endosalpingeal responses in four different experimental models in which the numbers and presumptive activity of suspended follicular cells are varied in pigs with spontaneous oestrous cycles. Because these animals ovulate on both ovaries, epithelial activity can be compared and contrasted between the two sides. In a final model, attempts are being made to generate early pregnancy responses in the absence of embryos by transplanting zygote-programmed cumulus cells from a mated donor into the Fallopian tube of an unmated recipient.