Blastocyst is the source of prostaglandins in the implantation site in the rabbit.

The levels of prostaglandins (PGs) were measured by radioimmunoassay in the interimplantation and the implantation sites as well as in the implantation site without the blastocyst in the rabbit on day 7 of pregnancy (168 h post coitum). The concentrations of PGs were also determined in the blastocyst (PGF:101.59+/-4.33 and PGE-A:29.74+/-3.11 ng/blastocyst, n=6) and the blastocoel fluid (PGF:253.55+/-39.56 and PGE-A:83.29+/-6.60 ng/100 microliters, n=4) on day 7. The levels of both PGF and PGE-A were significantly higher in the implantation site as compared to interimplantation site (PGF:73.63+/-6.68 vs. 0.59+/-0.21 and PGE-A:25.52+/-3.30 vs. 1.22+/-0.18 ng/100 mg wet weight, n=8). The removal of the blastocyst from the implantation site drastically reduced the concentrations of PGs in this site (PGF:8.71+/-2.80 and PGE-A:1.64+/-0.12 ng/100 mg wet weight, n=8). The results provide evidence that the blastocyst is the major source of PGs which contribute to the high concentration in the implantation site in the rabbit.