Egg transport and postcoital isthmic contractility in the rabbit

Both pre- and postcoital isthmic contractility were recorded in vivo in the rabbit by using balloon-ended catheters, filled with fluid and placed in the isthmic lumen of the oviduct. Autopsy was performed at 12, 24, 48 and 72 hours postcoitum (PC). Segmental flushing of the contralateral oviducts correlated isthmic contractility with egg transport. At 12 and 24 hours PC, when the majority of eggs reached the ampulla, the isthmic activity increased, involving both active contractions and resting pressure fluctuation. This active pattern caused an increase in the isthmic intraluminal pressure on occlusion of the isthmus and retention of the eggs at the ampullary-isthmic junction. At 48 hours PC, when the majority of eggs were in the distal isthmus, there were a uniformly low amplitude and highly frequent resting pressure fluctuations without any active contractions. Such a pattern reduced the isthmic luminal diameter, with subsequent isthmic egg locking. At 72 hours PC, when the eggs were transported to the uterus, complete cessation of the isthmic contractility, including resting pressure fluctuations, was associated with abrupt and remarkable alterations in the resting baseline. Since the estimated diameter of the egg, with its mucin coat, was bigger than that of the resting isthmus, the eggs initiated their own transport through the isthmus by stretching the adjacent walls.