HORMONE-SECRETION BY PREIMPLANTATION EMBRYOS IN A DYNAMIC INVITRO CULTURE SYSTEM

Bovine embryos recovered from superovulated donors on Days 8-18 postestrus were cultured in vitro in a tissue perifusion system to quantify hormone secretion. Embryos were cultured for 24 h at 37-degrees-C in Ham's F-10 medium supplemented 5% v/v with heat-treated, charcoal-stripped calf serum; 100 IU/ml penicillin; and 100-mu-g/ml streptomycin. The medium was saturated with 5% CO2 in air and perifused at 50-mu-l/min (3 ml/h). Estrone (E1), estradiol (E2), progesterone (P4), prostaglandin E2 (PGE2), and prostacyclin (PGI2) were quantified by RIA in 6-h pools of perifusate fractions. Estrone was measurable (pg/h/embryo; mean +/- SE) on Days 13 (10.80 +/- 4.56) and 15 (34.80 +/- 9.80); E2 on Days 11 (36.80), 12 (81.28 +/- 29.80), 13 (11.75 +/- 4.09), 15 (157.20 +/- 112.60), and 16 (30.26 +/- 8.76); and P4 (ng/h/embryo) on Days 13 (0.5-1.0) and 17 (approximately 1.5). PGE2 was secreted by Day 10 bovine embryos during the last 6 h of culture (19-24 h) and throughout culture for Day 11-18 embryos. The rate of PGE2 secretion increased (p < 0.05) over the previous days(s) at Days 13 and 17. The mean (+/- SE) secretion rates (pg/h/embryo) for the 24-h culture by embryonic ages were as follows: Day 11 (63.39 +/- 14.61), 12 (172.10 +/- 30.90), 13 (3094.08 +/- 283.35), 14 (1633.89 +/- 49.98), 15 (3739.23 +/- 1082.79), 16 (4955.37 +/- 1381.83), 17 (11893.23 +/- 1188.48), and 18 (13827.99 +/- 3587.88). PGI2 secretion, as measured by 6-keto-PGF(1-alpha), was also evident by Day 10, with increases (p < 0.05) occurring on Days 12, 16, and 17. The per-embryo mean (+/- SE) secretion rates (pg/h) for the culture period were as follows: Day 10 (18.30 +/- 0.39), 11 (13.80 +/- 0.75), 12 (45.18 +/- 1.46), 13 (65.79 +/- 1.56), 14 (73.80 +/- 1.56), 15 (79.75 +/- 2.13), 16 (210.09 +/- 5.88), 17 (1160.81 +/- 41.70), and 18 (1301.03 +/- 60.06). Porcine embryos (Days 10 and 11), used to validate the ability of the assay to detect estrogens in perifusate fractions, secreted all hormones, but rates declined over time. These data indicate that bovine embryos secrete several hormones that may, because of quantity and timing, be involved in maternal recognition, establishment, and maintenance of pregnancy.