Category Archives: Placenta

Autoradiographic Localization and Characterization of Angiotensin II Receptors: DISCUSSION(6)

DISCUSSION(6)

This is in accordance with previous findings. In the present study, enzymatically inactive renin (prorenin) was not determined. In an earlier study, however, no prorenin was detected in the bovine placenta. This is in contrast to the human placenta, which—withthekidney—is amain source of the increased prorenin in the plasma during pregnancy. The active renin concentration is the rate-limiting factor for the formation of Ang I, which is rapidly converted to Ang II by the ubiquitous angiotensin-converting enzyme. The finding that active renin was very low or undetectable in the bovine placenta indicates a low formation rate of Ang II in this tissue. Other enzymes, however, are capable of forming angiotensin from angiotensin-ogen. In the present study, the specific renin inhibitor remikiren abolished all formation of Ang I in the renin assay, indicating that no other Ang I-forming enzymes are present in the bovine placenta. ventolin inhaler

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: DISCUSSION(5)

In the placentomes, we found a predominance of AT2 receptors. The highest proportion of AT1 receptors, determined by Ang II receptor binding studies, was found at the beginning of the gestation. However, autoradiography showed that the AT1 receptors were placed mostly on the maternal side, whereas the AT2 receptors predominated on the fetal side. In the early placentome, no stalk has developed to indicate a natural border towards the endometrium. Our finding of a higher proportion of AT1 receptors in the first part of gestation probably reflects a higher content of maternal tissue in the early placentomes.

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: DISCUSSION(4)

DISCUSSION(4)

In contrast to the classical Ang II target tissues, which contain mostly AT1 receptors, the majority of the fetal Ang II binding sites are AT2 receptors. They are located in the fetal skin, skeletal muscle, and mesenchymal cells and disappear after birth. On the basis of the location and ontogenicity of the expression of the AT2 receptors, it was suggested that they may be involved in cell differentiation and growth. Recent experiments using vascular tissue cultures showed that the AT2 receptors exert an mtiprolifera-tive effect by counteracting the AT1 receptor growth-promoting effect. Buy Asthma Inhalers Online

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: DISCUSSION(3)

In the human syncytiotrophoblast, the AT1 receptors were localized on the basolateral plasma membranes. Recent in vitro studies using human trophoblast cells have demonstrated that Ang II stimulated human placental lactogen and specific (31-glycoprotein secretion through the AT receptor. As shown in Figure 8, we found no binding of 125I-[Sar1-Ile5-Ile8]-Ang II to the bovine placental lactogen-producing binucleate and trinucleate cells situated in the trophoblast cell layer and maternal uterine epithelium. This finding suggests that Ang II does not regulate the secretion of placental lactogen in the bovine placenta, in contrast to the findings in the humans. birth control pills

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: DISCUSSION(2)

DISCUSSION(2)

Autoradiography showed a marked 125I-[Sar1-Ile5-Ile8]-Ang II binding in the intercotyledonary membrane and the placentome, whereas the binding to the allantoamnionic membrane appeared less intense. Data from Ang II receptor binding studies showed, however, that the amount of receptor related to the extracted cell membrane protein (Table 2) was lower in the placentome than in the allantoamnionic and intercotyledonary membrane. The allantoamnionic membrane is a tissue that contains relatively few scattered cells, whereas the intercotyledonary membrane and the pla-centome have a much higher cell density. flovent inhaler

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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

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: RESULTS(6)

RESULTS(6)

Apparently, the mesenchymal cells differed with respect to Ang II receptor expression, since cells within the same area showed marked differences in Ang II binding (Fig. 9).

The 125I-[Sar1-Ile5-Ile8]-Ang II binding in the allantoam-nionic membrane was always relatively weak (data not shown). It occurred mainly in the mesenchyme in close relation to the allantoic endoderm and amnionic ectoderm, and around the few arteries. The predominant Ang II receptor type was the AT2 receptor. The allantoic endoderm and amnionic ectoderm did not reveal any binding.

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: RESULTS(5)

In the allantochorionic membrane of the placentomes (cotyledon), the AT2 receptor was also the most abundant Ang II receptor type (Figs. 6a and 7c). Most binding occurred on the mesenchymal cells at the fetal side of the cotyledon and at the lower-order fetal villi (Fig. 6a). This binding disappeared in the higher-order villi. Specific binding to the tunica media of the arteries was observed in only a few arteries and was always scarce.

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: RESULTS(4)

RESULTS(4)Renin Concentrations

The renin concentrations in bovine placentae and fetal membranes (Table 4) were low or, in several animals, even below the detection limit (0.014 GU/kg wet tissue weight). In the intercotyledonary membrane and the allantoamnionic membrane, no renin could be detected during the first part of gestation. All measured renin was completely inhibited by the specific renin inhibitor remikiren, indicating that no nonrenin enzymes, capable of forming Ang I, were present in the placenta and fetal membranes. buy ampicillin

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Autoradiographic Localization and Characterization of Angiotensin II Receptors: RESULTS(3)

Angiotensin II Receptor Densities

The amount of Ang II receptor, related to the protein in cell membrane fractions from placentae and fetal membranes of various stages of gestation, is given as fmol/mg membrane protein and is shown in Table 2. The amount was lower in the placentome than in the intercotyledonary allantochorionic membrane (p < 0.001) and the allantoamnionic membrane (p < 0.001). It changed during gestation in the placentome (p < 0.005) and the intercotyledonary membrane (p < 0.02), but it did not change in the allan-toamnionic membrane. ventolin inhalers

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