THE EFFECT OF THE OVIDUCT, UTERINE, AND IN-VITRO ENVIRONMENTS ON ZONATHINNING IN THE MOUSE EMBRYO

Objective: To evaluate the impact of the oviduct, uterine, and in vitr o environments on zona pellucida thinning in the mouse embryo. Design: Female mice were stimulated with pregnant mare serum gonadotropin and mated after hCG injection. Unilateral oviduct ligation was performed on day 2 of gestation using the dorsal approach. The mice were divided into equal groups and killed on days 2, 3, 4, 5, and 10 of gestation. In vitro incubated embryos served as controls. Average daily zona thi ckness measurements were subjected to analysis of variance and paired Student's t-test. Setting: The laboratory of the assisted reproductive program of Rush University Medical Center. Main Outcome Measure(s): P rogressive daily decrease in average zona thickness.Result(s): Zona me asurements of embryos flushed out of uterine horns, Ligated oviducts, and in vitro incubation demonstrated statistically significant decreas es in zona thickness, from 9.6 +/- 1.6 mu m (day 3) to 6.0 +/- 0.8 mu m (day 5), from 11.6 +/- 2.2 mu m (day 2) to 6.0 +/- 1.6 mu m (day 5), and from 11.1 +/- 2.0 mu m (day 2) to 6.0 +/- 1.6 mu m (day 5), respe ctively. There were no differences in average zona thickness for embry os in the same cell stage and same protocol day in all three locations . Conclusion(s): Zona thinning seems to be induced primarily by the di viding embryo before implantation. A substantial tubal and uterine con tribution to zona thinning was not detected in this mouse embryo model . (C) 1997 by American Society for Reproductive Medicine.