Influence of a stable prostacyclin analogue (iloprost) and cyclooxygenase inhibition on angiotensin-II in the perfused human placenta.

Studies were undertaken on perfused human placentas to examine the effect of a stable prostacyclin analogue (iloprost) on the angiotensin-II (A-II) response in the placental vessels, and to examine how this response is influenced by cyclooxygenase inhibition. Iloprost, in doses of 1, 5, and 10 micrograms significantly reduced the response of 50 micrograms of A-II. The vasoconstriction produced by the autacoid was attenuated by the three doses of iloprost by 43.9 +/- 5.2%, 56.5 +/- 6.1%, and 39.7 +/- 6.0%, respectively (MEAN +/- S.E.). The 1 microgram dose of the analogue did not differ significantly from either the 5 micrograms or 10 micrograms dose in this regard. A 5 mg dose of the cyclooxygenase inhibitor indomethacin, when combined with 1 microgram of iloprost, also significantly attenuated the A-II response, although the dilating effects of iloprost was significantly reduced by indomethacin. This response of the autacoid was significantly reduced when compared to the A-II response preceded by only iloprost. Because the effects of A-II were attenuated by indomethacin, it is suggested that part of the mechanism of A-II is due to prostaglandin release into the placental circulation, the majority of which appear to have a pressor effect on the placental vessels.