Ovary

Changes in Vascular Perfusion of the Endometrium in Association with Changes in Location of the Embryonic Vesicle in Mares

Abstract
The equine embryonic vesicle is mobile on Days 12-14 (Day 0 = ovulation), when it is about 9-15 mm in diameter. Movement from one uterine horn to another occurs on average about 0.5 times per hour. Mobility ceases (fixation) on Days 15-17. Transrectal color Doppler ultrasonography was used to study the relationship of embryo mobility (experiment 1) and fixation (experiment 2) to endometrial vascular perfusion and uterine blood flow. In experiment 1, 8 nonpregnant and 16 pregnant mares were examined by color Doppler daily from Days 1-16. Endometrial vascularity (scored 1-4, none to maximal) did not differ on Days 1-8 between nonpregnant and pregnant mares or between the sides with and without the corpus luteum. Endometrial vascularity scores were higher (P < 0.05) in both horns of pregnant mares than in nonpregnant mares on Days 12-16. In pregnant mares, the scores increased (P < 0.05) in the horn with the embryo between Days 10-12 and were higher (P < 0.05) than in the opposite horn on Days 12-15. In experiment 2, 14 pregnant mares were examined from Day 13 to 6 d after fixation. Beginning on the day of fixation, endometrial vascularity scores and number of colored pixels per cross section of endometrium were greater (P < 0.05) in the endometrium surrounding the fixed vesicle than in the middle portion of the horn of fixation and were greater (P < 0.05) in the middle portion of the horn of fixation than in the opposite horn. Time averaged maximum velocity of an artery at the mesometrial attachment was greater (P < 0.05) for the horn of fixation than for the opposite horn. Results supported the hypothesis that transient changes in endometrial vascular perfusion accompany the embryonic vesicle as the vesicle changes locations during embryo mobility.

Key words: Embryo • Pregnancy • Conceptus • Uterus

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