Prostaglandin E2 secretion by oviductal transport-stage equine embryos

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 “S-methionine/cysteine, ‘H.progesterone, or 5H.arachidonic acid for 24 h, and subse-quently 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) E,/ embryo, 1.0 ± 0.2 pg of 1 7a-hydroxy progesterone/embryo, 4.8 ± 0.6 pg of androstenedione/embryo, and 11.5 ± 4.5 pg of PGF,,./embryo. They did not secrete detectable quantities of protein, testosterone, or estradiol-17. A second experiment was conducted to measure temporal changes in embryonic PGE, 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 ‘H-arachidonic acid for 24 h, and the concentration of ‘l-I-PGE, in the culture medium was subsequently measured by HPLC. Embryos did not secrete detectable amounts of PGE, prior to the expected time of oviductal transport (Day 3 and Day 4). They secreted 5.7 ± 1.0 pg of PGE,/embryo immediately before and during the expected time of oviductal transport (Day 5), and they secreted significantly (p < 0.01) higher amounts (42.0 ± 11.5 pg) of PGE,/embryo immediately after uterine entry (Day 6). Embryonic PGE, secretion was also detected on Day 6 by MA (271.0 ± 39.1 pg/embryo; n = 8 embryos). Demonstration of a temporal association between embryonic PGE, secretion and the oviductal transport period indicates that embryonic PGE, may initiate oviductal transport in the mare