Autoradiographic Localization and Characterization of Angiotensin II Receptors: DISCUSSION(1)

The bovine placenta and fetal membranes contained high densities of Ang II receptors in all three stages of gestation. By using type-specific nonpeptide Ang II antagonists, Ang II receptor binding studies as well as autoradiography showed that these Ang II receptors were predominantly AT2 receptors. This is in accordance with recent findings in the pig but differs from findings in the human placenta, in which most Ang II receptors were AT1 receptors. The bovine and the porcine placenta are both epitheliochorial, with the bovine of the subtype synepitheliochorial, whereas the human placenta is hemomonochorial. It is very likely that the type of Ang II receptor that predominates in the placenta relates to the differences in placental architecture. buy ortho tri-cyclen

Autoradiography indicated the presence of non-AT 1/non-AT2 Ang II binding sites at very low densities in the bovine fetal membranes as well as in the placentome. By a visual estimate, these binding sites represented 1% or less of the total amount of Ang II receptors, and they were undetectable in the Ang II receptor binding studies. AT and AT2 receptor antagonist concentrations of 5 ^M, which are much higher than their IC50 values, were used in order to displace the 125I-[Sar1-Ile5-Ile8]-Ang II binding. Although both losartan and PD 123319 were used together at these high concentrations, specific binding was observed in the lower-order septa of the maternal crypts and in the fetal membranes. Non-AT1/non-AT2 Ang II binding sites have previously been reported in the human endometrium, but to the knowledge of the authors, no previous reports of non-AT1/non-AT2 Ang II binding sites in the fetal membranes have been made.

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