Relationship between Changes in Volume of the Oviductal Fluid in the Ampulla and the Descent of Ovulated Eggs from the Ampulla to the Isthmus in Mice

Follicular growth and ovulation were induced in mice by administration of pregnant mare serum gonadotrophin (PMSG) followed 2 days later by human chorionic gonadotrophin; the day of PMSG injection was designated as day 0. The volume of the ampulla was measured and the location of the ovulated eggs determined at 06:00, 10:00, 14:00, 18:00 and 22:00 on day 3, and at 02:00 and 06:00 on day 4. The volume of the ampulla and hence oviductal fluid, peaked at 14:00 on day 3 and then declined. In all oviduct samples taken up to 14:00 on day 3, eggs were found exclusively in the ampulla. Thereafter, an increasing number of eggs were observed in the isthmus. Thus, the migration of eggs from the ampulla to the isthmus was concurrent with the decrease in oviductal fluid volume. The peak in the volume of oviductal fluid seen at day 3 is likely to coincide with the opening of the ampullary-isthmic junction of the oviduct.