The effects of the components of the renin-angiotensin system on the isolated perfused human placental cotyledon

Angiotensins I, II, and III, renin substrate, and des-Asp¹-angiotensin I were injected as a bolus into either the maternal or fetal circulation of human placental cotyledons perfused in vitro. All drugs tested produced dose-related increments in fetal perfusion pressure when injected into the fetal circulation, with the order of potency being angiotensin I ≈ angiotensin II ≈ angiotensin III ≳ des-Asp¹-angiotensin I ≳ renin substrate. The responses to all the drugs could be blocked by the competitive inhibitor of angiotensin II, (Sar¹, Ala⁸)-angiotensin II, but only the actions of angiotensin I, renin substrate, and des-Asp¹-angiotensin I could be blocked by angiotensin converting enzyme inhibitor. When the agents were injected into the maternal circulation, only angiotensins II and III caused dose-related increments in fetal perfusion pressure. Possibly, the placenta may be the main site of conversion of angiotensin I to angiotensin II in the fetoplacental unit, and angiotensin II produced by the placenta could act locally to control fetoplacental blood flow.