This study was conducted to identify embryonic products whose secretion was temporally associated with the oviductal transport period of the mare. Chemicals secreted by oviductal-transport-stage equine embryos were identified by incubating Day 6 or Day 7 early uterine embryos with 35S-methionine/cysteine, 3H-progesterone, or 3H-arachidonic acid for 24 h, and subsequently identifying radioactively labeled proteins (SDS-PAGE; n = 3 embryos), steroids (HPLC; n = 3 embryos), or prostaglandins (HPLC; n = 3 embryos) in the culture medium. Early uterine embryos secreted 116.1 +/- 45.5 pg of prostaglandin (PG) E2/embryo, 1.0 +/- 0.2 pg of 17 alpha-hydroxy progesterone/embryo, 4.8 +/- 0.6 pg of androstenedione/embryo, and 11.5 +/- 4.5 pg of PGF2 alpha/embryo. They did not secrete detectable quantities of protein, testosterone, or estradiol-17 beta. A second experiment was conducted to measure temporal changes in embryonic PGE2 secretion during the oviductal and early uterine period. Day 3, Day 4, Day 5, and Day 6 embryos (n = 8 embryos/day) were incubated with 3H-arachidonic acid for 24 h, and the concentration of 3H-PGE2 in the culture medium was subsequently measured by HPLC. Embryos did not secrete detectable amounts of PGE2 prior to the expected time of oviductal transport (Day 3 and Day 4). They secreted 5.7 +/- 1.0 pg of PGE2/embryo immediately before and during the expected time of oviductal transport (Day 5), and they secreted significantly of PGE2/embryo immediately before and during the expected time of oviductal transport (Day 5), and they secreted significantly (p less than 0.01) higher amounts (42.0 +/- 11.5 pg) of PGE2/embryo immediately after uterine entry (Day 6).(ABSTRACT TRUNCATED AT 250 WORDS)
The hypothesis that treatment of pregnant mares with prostaglandin E2 (PGE2) hastens the oviductal transport of equine embryos was tested by treating bred mares with PGE2 on Day 3 after ovulation and subsequently measuring the rate of hastened oviductal transport (estimated by the uterine embryo recovery rate on Day 4 after ovulation). In a preliminary, noncontrolled experiment, oviductal transport was apparently not hastened after intramuscular, intrauterine, or intraperitoneal PGE2 administration to bred mares (0/6, 0/3, and 0/3 mares, respectively). Oviductal transport appeared to be hastened in 1/13 mares after a single intraoviductal administration of PGE2, and in 2/2 mares after continuous intraoviductal administration of PGE2. In a subsequent, controlled experiment, treatment with a continuous intraoviductal infusion of PGE2 hastened oviductal transport in significantly more (p less than 0.01) mares versus a continuous intraoviductal infusion of vehicle or no treatment (6/11 vs. 0/11 or 0/11 mares, respectively). Unfertilized oocytes and oviductal masses were also recovered from mare uteri after continuous intraoviductal PGE2 administration, but were not recovered after vehicle administration or no treatment. These results support the hypothesis that PGE2 treatment hastens the oviductal transport of equine embryos, and suggest a role for embryonic PGE2 in the initiation of selective oviductal transport in the mare.
The hypothesis that equine embryos initiate oviductal transport in mares was tested by placing day 6 uterine embryos in the oviducts of day 2 (n = 10) or day 5 (n = 10) recipient mares and attempting to collect the embryos from the uterus 48 h later. To determine whether the surgical transfer procedure initiated oviductal transport, medium alone was placed in the oviducts of day 2 (n = 10) inseminated mares (sham transfer), and uterine embryo collections were attempted 48 h later. Embryos were transported through the oviduct of day 2 recipients by day 4 (instead of day 5 to 6) in six of ten mares, which was not significantly less (P greater than 0.1) than in day 5 recipients (9 of 10). Oviductal transport was not primarily initiated by the surgical transfer procedure, since oviductal transport occurred in only one sham transfer. There was no significant difference (P greater than 0.1) in the diameter of embryos placed in the oviducts of day 2 and day 5 recipient mares (180 +/- 13.8 versus 187 +/- 11.3 microns, respectively). However, embryos collected from the uterus were significantly smaller (P less than 0.05) in day 2 than in day 5 recipients (375 +/- 85.4 versus 659 +/- 43.6 microns, respectively). One uterine embryo had shed its zona pellucida before being placed in, and transported through, the oviduct of the recipient mare.
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