Objective: A recent study on the distribution of angiotensin II (ANG II), ANG II (AT) receptors, and human placental lactogen in human placental tissues from term pregnancies showed positive correlations among these indices, suggesting an important role for ANG II in placental endocrinology. However, nothing is known about the ontogenesis of this functional role for ANG II during pregnancy. Therefore, the aim of this study was to investigate the placental AT receptor expression at various trimesters of pregnancy. We also studied the ontogenesis of phospholipase C-linked G alpha q/11 protein, which is known to transduce ANG II type-1 (AT1) receptor signal.
Methods: Western blot analysis of placental membrane proteins was performed using a chemiluminescence kit and specific antibodies against AT1 receptor and G alpha q/11 protein. Northern blot analyses of AT1 receptor and G alpha q/11 mRNA expression were accomplished using random primed [32P]dCTP-labeled specific probes.
Results: The autoradiographs of AT1 receptor mRNAs (2.4 kb) and proteins (83 kDa) showed a progressive 4.8-fold and 2.6-fold increase, respectively, during pregnancy, with maximal levels at term. We also observed progressive 1.8-fold and 4.5-fold increases of G alpha q/11 protein (43 kDa) and mRNAs (4.5, 6.0, and 7.1 kb), respectively, during pregnancy, with maximal levels observed at term.
Conclusion: Our results demonstrate that both the human placental AT1 receptor content and the G alpha q/11 protein level increase during pregnancy, and suggest that the AT1 receptor pathway may play a role in human placental physiology.