Some observations on sperm transport through the uterotubal junction of the rat

Entry of spermatozoa into the oviducts of mammals is restricted by the uterotubal junctions. The extent to which these junctions act as selective valves, or filters, for sperm transport has not been determined. A new technique has been developed that permits the direct visualization of sperm transport through the uterotubal junction of the rat in vitro. After mating or artificial insemination, the female tract is removed to a special "observation dish" containing oxygenated Earle's solution maintained at 37 degrees C. The oviducts are severed 1.0 - 1.5 mm above the uterotubal junctions. Under appropriate magnification and with oblique transillumination, spermatozoa may be observed emerging from the cut ends. It was noted that only motile spermatozoa emerged and that they usually appeared individually, with an interval of several minutes between each. Their egress was not directly related to contractions of the uterine cornu. Neither immotile spermatozoa nor a dye solution were observed to pass through the uterotubal junction. It is concluded that sperm motility is important, and probably essential, for sperm entry into the oviducts in the rat. Scanning electron microscopy revealed that the rat uterotubal junction forms a small mound or papilla projecting into the uterine cavity. No ciliated cells were observed in this region.