Blastocyst attachment in the ovariectomized rat treated with an intrauterine injection of luteinizing hormone-releasing hormone (LRH).

Pregnant rats were bilaterally ovariectomized on day 3 and the blastocysts were maintained in a state of delayed implantation by the daily sc injection of 4 mg progesterone from day 3 to 6. On the morning of day 6 the rats received an intrauterine injection of 1 mg LRH in the right horn. A second group of rats was treated as above and was additionally injected with 2 mg of indomethacin on day 5 and 1 mg on the morning of day 6. Fifteen min prior to autopsy the animals were injected iv with a 0.5% solution of Evans Blue. The presence of uterine blue bands and the number of blastocysts recovered from the right and left (control) horns were recorded at 0.25, 0.5, 1.2 and 4 h after the injection of LRH. It was determined that the number of blastocysts flushed from the treated horn was significantly reduced below that of the control left horn within 15 min and at every autopsy interval thereafter. In addition, blue bands appeared in the treated horn as early as 15 min after the injection of LRH demonstrating that implantation had occurred in a few instances. No blue bands appeared in the control horns. The injection of indomethacin did not inhibit the attachment or implantation of blastocysts or the presence of blue bands in the treated horn. A possible role for blastocyst oestrogen is discussed.