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Dynamic physical interactions between the equine embryo and uterus
Author(s) -
GINTHER O. J.
Publication year - 1985
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.1985.tb04592.x
Subject(s) - conceptus , uterus , uterine horns , vesicle , ovulation , biology , embryo , anatomy , andrology , pregnancy , endocrinology , fetus , medicine , microbiology and biotechnology , genetics , membrane
Summary Repealed examinations of mares with real‐time ultrasound echography demonstrated that the well‐known phenomenon of transuterine migration of the equine conceptus is not a simple one‐way passage. Instead, the embryonic vesicle was shown to bypass its eventual site of attachment many times per day while traversing the full length of each uterine horn and the uterine body. The embryonic vesicle showed limited mobility on Days 9 and 10 post ovulation when it spent more than 60 per cent of the time in the uterine body. Maximum mobility occurred on Days 11 to 14. Location changes within a uterine horn were more likely to be progressive when the vesicle was moving in a caudal direction, whereas location changes within the body were more likely to be progressive when the vesicle was moving in a cranial direction. Individuals of twin conceptuses had mobility patterns similar to those of singletons. Administration of a sympathomimetic blocking agent reduced the extent of mobility, indicating that uterine contractions are the propulsive force for vesicle mobility. Water‐filled balloons acting as simulated vesicles were also mobile when placed in the uterus on Days 12 or 13 of dioestrus, but their rate of movement was less than that of embryonic vesicles. It is suggested that the mobility of the embryonic vesicle may play a role in blocking the uterine luteolytic mechanism. Cessation of vesicle mobility (fixation) occurred on Day 15, 16 or 17 and it remained firm with no further movement between horns. Twin embryos exhibited a preference for unilateral fixation (70 per cent). Fixation may be a function of expansion of the embryonic vesicle combined with intraluminal resistance to mobility resulting from increasing uterine tone. The site of fixation was in the caudal portion of one of the horns, perhaps because of the curvature of the horns at that point. The concept of extensive mobility of the equine conceptus provides rationale for the development of hypotheses concerning the perplexing effects of reproductive status on the site of fixation and the consistency of fixation of the vesicle in the caudal portion of a uterine horn. Orientation is defined as rotation of the vesicle so that the embryonic pole is located ventrally, opposite the mesometrial attachment of the uterus. It is proposed that orientation takes place between the day of fixation and Day 19 when the embryo proper is first detectable by ultrasound. Orientation is attributable to disproportionate encroachment of the dorsal uterine wall, a massaging action by uterine contractions and greater thickness of the vesicle wall at the embryonic pole.