Effect of particle size on time course of transport of surrogate ova through the rabbit oviduct.

The time-course of transport of plastic microspheres of 100, 200, 400, 800, and 1000 mu diameter through the rabbit oviduct was studied under various hormonal conditions. During estrus, the rabbit oviduct rapidly transports particles of 200 mu diameter to the uterus. After ovulation, the passage of these particles is delayed, first at the ampullary-isthmic junction, and then along the isthmus, perhaps influenced by a second site of resistance at the uterotubal junction. Particles of 100 mu diameter are not subject to these delays but pass rapidly to the uterus. Our data support the idea that the rapid passage of 100-mu spheres reflects a size-related inability of the resisting "gates" to limit their passage. Pharmacologic doses of estrogen act to prolong or increase the resistance to particle passage at the ampullary-isthmic junction and apparently also accelerate transport through the isthmus. Progesterone presumably increases the efficiency of the "gate" at the ampullary-isthmic junction, hastens transport through the isthmus, and seems to "open the gate" at the utero-tubal junction. Further experiments are required to prove or negate these inferences.