Rabbit Blastocysts Accumulate [3H]Prostaglandinsin Vitro*

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Abstract
Rabbit blastocysts obtained on days 5, 6 and 6.8 of pregnancy were incubated in vitro in Tyrode''s buffer with 3H-labeled prostaglandins (PG). Accumulation of PG was studied, using Whatman GF/F filters to separate bound and free ligands. The uptake and efflux of [3H]PG were studied as a function of PG type, incubation time, temperature, and effect of metabolic inhibitors as well as age and number of blastocysts. Blastocysts of the same age accumulated approximately the same amount of [3H]PGE2 and [3H]PGF2.alpha. from their environment, however, there was no apparent saturation over a PG concentration range of 1-1000 nM. Both the uptake and efflux of PG were age dependent, with older blastocysts accumulating more PG. Approximately 90% of the [3H]PG appear to be transported into the blastocoelic fluid, with little PG remaining in the blastomeres. PG accumulation was relatively insensitive to azide, ouabain, cyanide, or bromcresol green, but was affected by incubation at 0.degree. C or the addition of indomethacin (10 .mu.g/ml). No catabolism of the accumulated PG was observed. The release of PGE2 in general did not differ from that of PGF2.alpha. except on day 6.8 of pregnancy when PGE2 was released more rapidly than on day 6. Rabbit blastocysts can accumulate PG from their environment, which may imply a storage potential in the blastocyst and release before implantation.

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