Effects of iloprost, a stable prostacyclin analog, PGE2 and PGF2 alpha on rabbit blastocysts

The uptake of prostaglandins (PGs) into day-6 rabbit blastocysts was studied. Uptake of PGE2 and PGF2 alpha was temperature sensitive and nonsaturable up to 1,000 nM external concentration. In contrast, uptake of Iloprost, a stable prostacyclin analog, was unaffected by temperature, and showed apparent saturation at greater than 2 nM concentration. Individual blastocysts exposed to 0.2 microM radioinert prostaglandins or 1 hr did not swell significantly. Blastocyst concentration of PGF2 alpha was 4.8 +/- 2.1-fold higher than that of PGE2, which was 9.5 +/- 2.4-fold greater than that of 6-keto-PGF1 alpha (the stable metabolite of prostacyclin). Uptake of tritiated water was increased by exposure of blastocysts to 0.2 microM PGE2 or PGF2 alpha, but not to Iloprost. Thus, imbibition of water does not cause blastocyst swelling at least during limited in vitro culture. It is concluded that prostacyclin is of less importance in blastocyst function than PGE2 or PGF2 alpha.