Intrauterine migration of the porcine embryo: coordination of bead migration with estradiol.

Forty crossbred gilts were used in three experiments to examine the effects of estradiol on embryo migration. Small, spherical beads of Silastic glue containing either cholesterol or estradiol-17 beta were used to mimic embryo migration. In the first experiment, 10 cholesterol- and 10 estradiol-impregnated beads were injected into the tip of the uterine horns, either on the same side (n = 5) or opposite from each other (n = 5). The second experiment consisted of a localized release of cholesterol or estradiol and observing migration of cholesterol-containing beads inserted 10 cm anterior and posterior to this site (n = 5). In the third experiment, 10 cholesterol-impregnated beads were injected into either the tip or base of one uterine horn. Additionally, these gilts were exposed to vehicle or exogenous estradiol in a 2 X 2 factorial arrangement of treatments (n = 5). Results of these experiments indicated that cholesterol-impregnated beads migrated further (P less than .05) when adjacent to estradiol-containing beads than when in an opposite uterine horn. Localized release of estradiol failed to induce movement of beads away from the site of steroid release. Finally, beads inserted at the base of the uterus moved anteriorly following treatment of gilts with estradiol. We suggest from these experiments that the porcine uterine horn cannot discriminate between estradiol- and cholesterol-releasing beads and, further, lacks a coordinated ability to displace adjacent beads. A site-dose dependent mechanism(s) of estrogenic induction of migration may exist such that porcine embryos become bilaterally intermixed following posterior, then anterior, waves of uterine contractions.