Summary. Microspheres of various materials and diameters were transferred microsurgically to the rat oviduct on Day 1 of pregnancy and autopsies were done at various times thereafter up to Day 10 to assess the recovery and segmental distribution of microspheres and eggs in the genital tract or the viability of embryos. The number and distribution of eggs in the treated and control sides after unilateral transfers were not different on Day 4 and 5 and the number of embryos implanted on Day 10 was not significantly affected after bilateral transfers.
The segmental distribution of eggs and starch microspheres within the oviduct on Days 2, 3 or 4 showed that both are transported partly intermingled from ampulla to uterus. When microspheres of poly(dl-lactide-co-glycolide), starch, dextran or dextran blue were transferred, their distribution in the genital tract in the morning of Day 5 showed that poly(dl-lactide-co-glycolide) and dextran microspheres stayed longer in the oviduct while starch and dextran blue microspheres were transported to the uterus at the same time as the eggs. Transfer of starch microspheres of 40–60 μm to one oviduct and 180–200 μm in diameter to the opposite oviduct showed that distribution on one side was nearly identical to that of the other side from Days 2 to 5.
We conclude that the behaviour of synthetic surrogate ova in rats differs from that in rabbits. The rat oviduct does not change the rate of transport of native eggs following transfer of synthetic surrogate ova. Also, in the rat the composition of the surrogates has greater influence than their size on their time of passage to the uterus. Some surrogates mimic quite well the oviducal transport of embryos and can be used therefore to study this process in species in which the eggs are not coated with additional layers after ovulation.
Keywords: rat; oviduct; embryo transport; egg surrogate; microsphere