Detrimental effects of prostaglandin F₂[alpha] on preimplantation bovine embryos

Two studies were performed to determine effects of prostaglandin F_{2 α} (PGF_{2 α}) on continued embryonic development of pre-compacted (in vitro-produced) and compacted (in vitro-derived) bovine embryos. In Experiment 1, pre-compacted (16-32 cell) in vitro-produced embryos were randomly assigned to receive either: 1) control (KSOM-PVA; n= 168); 2) PGF-1 (1 ng/mL PGF_2α in KSOM-PVA; n= 143); 3) PGF-10 (10 ng/mL PGF_2α in KSOM-PVA; n= 168); 4) PGF-100 (100 ng/mL PGF_2α in KSOM-PVA; n= 136), or 5) PGE-5 (5 ng/mL PGE₂ in KSOM-PVA; n= 62). Following four days of culture (5.5% CO₂, 7% O₂, and 87.5% N₂ at 38.5°C) in assigned treatments, development of embryos was determined by experienced technicians uninformed of treatments. Continued development of in vitro-produced 16- to 32-cell embryos (pre-compacted) to blastocyst was reduced by addition of PGF_2α in culture media (PGF-1, 30.4%; PGF-10, 41.4%; PGF-100, 33.3%, and control, 51.8%; P=0.002). In addition, culture of embryos in medium containing 1 ng/mL of PGF_2α had a more detrimental effect than addition of 10 ng/mL of PGF_2α (P<0.05). Furthermore, blastocyst development did not differ between control and PGE₂ treatments (P>0.10).

In Experiment 2, compacted (in vitro-derived) glycerol-frozen embryos were thawed and then allowed to regain normal morphology in holding medium for 30 min. Embryos were then sorted by stage of development and quality according with IETS guidelines for classification of bovine embryos. Compacted morula in the quality score of 1, 2 or 3 (n= 436) were randomly assigned to one of four treatments: 1) control (KSOM-PVA; n= 110); 2) PGF-0.1 (0.1 ng/mL PGF_2α in KSOM-PVA; n=108); 3) PGF-1 (1 ng/mL PGF_2α in KSOM-PVA; n=109); 4) PGF-10 (10 ng/mL PGF_2α in KSOM-PVA; n=109). After 24 h in culture (5.5% CO₂, 7% O₂, and 87.5% N₂ at 38.5°C), embryos were washed and placed in KSOM containing 0.5% BSA without PGF_2α for an additional 48 h. Embryo development was evaluated by experienced technicians uninformed of treatments. Continued development of in vitro-derived compacted morula to blastocyst was not affected by addition of PGF_2α to the culture medium (control, 68.1%; PGF-0.1, 58.9%; PGF-1, 61%, and PGF-10, 60%; P>010). However, hatching rates of embryos cultured with 0.1, 1 and 10 ng/mL PGF_2α were significantly lower than controls (24, 29.1, 24.5, and 44.5, respectively; P=0.05). No significant differences in hatching rates between doses of PGF_2α were observed. In conclusion, these studies suggest a direct negative effect of PGF_2α on continued embryonic development of pre-compacted and compacted bovine embryos. Responses to PGF_2α of pre-compacted (decreased blastocyst development) and compacted (decreased hatching rates) embryos may involve different mechanisms of action of PGF_2α depending on stage of development. In compacted embryos, PGF_2α may act through inhibiting completion of blastocoel formation and hatching; whereas, PGF_2α may have more dramatic effects by altering compaction in pre-compacted embryos.