Analysis of the Rabbit Uterine Fluid Collected by a Continuous Collecting Technique: Evidence for an Embryotoxic Component

An intra-abdominal flask (Hamner and Williams, 1963) was used for daily collection of uterine fluid. Some animals were kept with the flask for 3 consecutive pseudopregnancy cycles. Although the volume of fluid and the amount of proteins did not differ significantly from one cycle to another, the volume of fluid decreased after an hCG injection. The ratio of uteroglobin to albumin at Day 5 was found to be similar for uterine flushings of animals with flasks, uterine flushings of control animals and uterine fluid collected in the flask. Up to 50 % of the transferred morulae became expanded blastocysts after 2 days of in vitro growth in uterine fluid. The mean diameter reached by the expanded blastocyst was 0.62 mm when cultured in uterine fluid, while it was only 0.23 mm when cultured in heated rabbit blood serum. However, none of the pronuclei embryo developed properly in the uterine fluid. Similar results were obtained with the development of 1 cell embryos and morulae in uterine flushings. Ultrafiltration was used as a preliminary step for the separation of a low and high molecular weight fraction to characterize embryotoxic substances found in the uterine fluid. The inhibitory effect was found in the low molecular weight fraction which suggests that the toxic factor has a molecular weight of 500 daltons or less