[Experimental studies on the mechanism of implantation observed from PGF levels]

We have studied the synthesis and release of prostaglandin F by the rabbit blastocyst and endometrium coitum 144 hrs (day 6), 168 hrs (day 7) using RIA and a conversion experiment. The results obtained were as follows: Content of PGF in the blastocyst increased significantly (p less than 0.01) from day 6 to day 7. There was no significant difference in the content of PGF in the endometrium between the day 6 pregnant group, day 6 pseudopregnant group, day 7 pregnant non-implantation sites and day 7 pseudo-pregnant group. The value was significantly higher (p less than 0.05) on day 7 implantation sites compared to the others. A surge-like increase in PGF was observed in one hour incubation of day 6 blastocyst. On the other hand, an abrupt increase was observed after 3 hour incubation of day 6 pregnant endometrium. It was strongly suggested that day 6 blastocyst can convert 14C-arachidonic acid to PGF2 alpha in vitro. These results suggest that both the endometrium and the blastocyst are the sources of PGs involved in the process of implantation and that PGF emanating from blastocyst may play an important role in the beginning of implantation.