The Fallopian tubes in domestic mammals: how vital is their physiological activity?

Set in an historical perspective, this essay examines diverse physiological aspects of Fallopian tube function in domestic animals and man. Microsurgical experiments are described that established the role of the isthmus in imposing a sperm gradient up to the site of fertilisation. Resection of the isthmus followed by reanastomosis of the remaining portions of the tube generated a high incidence of polyspermy in mated animals. Scanning electron microscopy and surgical studies revealed that spermatozoa were arrested and stored in the caudal portion of the isthmus before ovulation, the so-called functional sperm reservoir. There were specific adhesion contacts between the sperm head and endosalpingeal microvilli or cilia. Further experiments indicated that very large numbers of competent spermatozoa could be released from pre-ovulatory binding by microinjections of a solution of progesterone in oil under the serosal layer of the tube: when suitably timed, such treatment led to a high incidence of polyspermic fertilisation. Avid sperm binding in the caudal isthmus before ovulation prevents myosalpingeal activity leading to abnormal fertilisation, as might occur with multiple mating. Temperatures in the reproductive system were assessed and the caudal isthmus was found to be cooler than the ampulla during the pre-ovulatory phase of sperm storage. Finally, the existence of fluid microenvironments within the Fallopian tubes was reported, and the role of suspended cumulus-corona cells in amplifying signals from the zygote examined. An impact of Fallopian tube fluids on embryonic gene expression was also considered--an influence that may be further imposed if such fluids have access to the uterine lumen.