Factors in mouse uterine fluid that inhibit the incorporation of [3H]uridine by blastocysts in vitro.

Fluid flushed from the uteri of "delayed implanting" and "implanting" mice was fractionated by gel-filtration. The fractions were freeze-dried, individually resuspended in culture medium containing [3H]uridine, and used for incubating "implanting" blastocysts. Several factors were found that reduced incorporation of [3H]uridine by the blastocysts. The amount of inhibitory activity in corresponding factors was generally similar in flushings from both types of uteri, but there was significantly more inhibitory activity in the void volume fractions of flushings from "delayed implanting" animals and it is suggested that this factor may be responsible for the metabolic dormancy of embryos during the diapause associated with delayed implantation.