[Angiotensin II receptors in the human placenta are type AT1]

Membrane angiotensin II receptors were measured in human placenta by means of 125I [Sar1 Ile8] All (angiotensin II antagonist) and characterized by using 2 other antagonists of angiotensin II: Dup 753 and CGP 42112A. These are specific and selective ligands which enable identification of AT1 and AT2 receptor subtypes respectively. The [Sar1 Ile8] All affinity is similar (Kd approximately 1 nmol.l-1) in the 3 different placental structures examined. However, the Bmax of villous tissues is approximately 9 times higher than that observed in chorionic plate but remains near that found in basal plate. In the central area of the placenta, mean values of 125I [Sar1 Ile8] All binding observed at a single concentration of 0.15 nmol.l-1 are 242 +/- 31 fmol/mg proteins in basal plate, 300 +/- 35 in villous tissues and 36 +/- 8 in chorionic plate. The umbilical vein and arteries respectively have 8.8 +/- 4.8 and 4.0 +/- 1.7 fmol/mg protein. The subtype analysis shows that only AT1 receptor is present in placental tissues. The Bmax values as well as those obtained by the relative measurement performed at a fixed 125I [Sar1 Ile8] All concentration of 0.15 nmol.l-1 indicate that the highest concentrations of angiotensin II receptors are found in placental villous tissues.