257 DEVELOPMENT OF HEAT-STRESSED OVA MATURED IN THE PRESENCE OF A PROSTAGLANDIN F_2α RECEPTOR ANTAGONIST

Abstract

Studies in the literature have shown that cumulus–oocyte complexes produce PGF_2α, that ova and cumulus cells have PGF_2α receptors, and that PGF_2α addition to maturing ova, above what would normally be produced, decreases blastocyst development. Because previous studies have shown elevated systemic and tissue levels of PGF_2α as a consequence of heat stress, it was hypothesized that detrimental effects of exposing maturing ova to elevated temperatures may be mediated in part through heat-induced increases in PGF_2α. To test this hypothesis, cumulus–oocyte complexes were matured at 38.5 or 41.0°C in the presence of a PGF_2α receptor antagonist (AL-8810). Preattachment embryo development of AL-8810-treated ova was compared with development of ova matured in media with or without diluent (DMSO added at the same concentration as AL-8810; diluent and developmental controls, respectively), resulting in 6 total treatment combinations. Data were analyzed as a randomized block design (blocking on oocyte collection date) with fixed effects of maturation temperature, AL-8810, and the respective interaction included in the statistical model. In experimental replicates in which the effects of heat stress decreased blastocyst development greater than 10% (n = 14), a significant maturation temperature × AL-8810 interaction was noted when evaluating blastocyst development (P = 0.05). Specifically, when ova were heat stressed during the first 12 h of in vitro maturation, blastocyst development was reduced in developmental and diluent controls (26.2 v. 18.8 and 24.4 v. 19.9, respectively; SEM = 1.6). In contrast, when ova were matured under the same conditions but in the presence of a PGF_2α receptor antagonist, the effects of heat stress to reduce blastocyst development after in vitro fertilization were no longer observed (22.5 v. 22.5; SEM = 1.6). When using abattoir-derived ovaries, it is not uncommon to collect, on occasion, ova that are developmentally challenged (i.e. blastocyst development is less than the 20 to 50% expected). In this experiment, this occurred on 5 occasions. Data from these experimental replicates were analyzed and reported separately because previous efforts had shown that the responsiveness of ova to changes in culture environment differs depending on the level of developmental competence. Relevant to this study, addition of AL-8810 to developmentally challenged ova matured under thermoneutral conditions increased cleavage (60.4 v. 55.4%, respectively; P = 0.06) and blastocyst development (17.7 v. 13.7%, respectively; P = 0.07). In summary, data illustrate that developmentally challenged ova, heat-stressed or otherwise, are susceptible to detrimental effects of PGF_2α. The ability to increase blastocyst development approaching or exceeding the values expected for competent ova suggests the usefulness of a PGF_2α receptor antagonist during in vitro maturation to improve the efficiency of in vitro production procedures.