Arachidonic acid metabolism by early ovine embryos and the role of prostaglandins in one aspect of embryonic development

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Virginia Tech

Most embryonal mortality occurs during early embryonic development. Two experiments were designed to study aspects of early embryonic development. Experiment 1 was to determine if early ovine embryos were capable of metabolizing arachidonic acid. Cyclic ewes were estrous synchronized with 6⍺-methyl-17β-hydroxy progesterone acetate (MPA) pessaries, superovulated with follicle stimulating hormone (FSH) and bred artificially. Embryos were collected on d 4, 8, 10, 12 or 14 of pregnancy and incubated with 1 μCi of [¹⁴C] arachidonic acid in an atmosphere of 5% CO₂, 45% O₂ and 50% N at 37°C for 24 h. Embryos from all days of pregnancy metabolized arachidonic acid to a number of compounds. Embryos produced primarily an unidentified polar compound, 6-keto-prostaglandin F₁⍺ (6-keto-PGF₁⍺), prostaglandin F₂⍺ (PGF₂⍺), prostaglandin E₂ (PGE₂), 13,14-dihydro-15-keto prostaglandin F₂⍺ (PGFM), prostaglandin B₂ (PGB₂) and 12L-hydroxy-5,8,10-heptadecatrienoic acid (HHT). Experiment 2 was to determine whether prostaglandins have a role in embryo hatching from the zona pellucida. Ewes were superovulated and bred artificially, and embryos were collected on d 7 of pregnancy. Embryos were incubated with ethanol (control), indomethacin, PGE₂ or indomethacin and PGE₂ in an atmosphere of 5% CO₂ and 95% air at 37°C for 24 h. Indomethacin appeared to decrease embryo hatching rate (indomethacin, 34.5% vs control, 46.4%). Prostaglandin E₂ appeared to increase embryo hatching rate (PGE₂, 60.0% vs. control, 46.4%). However, hatching rates for indomethacin and PGE₂ treatment groups were not different from control (P > .05). When compared to any group with indomethacin treatment, PGE₂ increased (P < .05) embryo hatching rate. The results of this study indicated that early ovine embryos can convert arachidonic acid to various compounds in vitro. Although not conclusive, indomethacin may decrease and PGE₂ may increase embryo hatching rate. Therefore, embryo-produced prostaglandins may be involved in hatching of sheep embryos from the zona pellucida.