Category Archives: Growth Factor

Differential Distribution of Binding Sites: DISCUSSION(8)

DISCUSSION(8)

Few specific activities have been especially attributed to the type 2 IGF receptor. However, stimulation of mesenchymal stromal cell and cytotrophoblast proliferation by IGF-II in the first trimester of gestation, together with the presence of IGF-II receptors on the villous cytotrophoblast, strongly suggests that IGF-II has an autocrine and/or paracrine action to control the growth of the placenta in relation to other peptides (endothelins). The IGF-II system is important in mice, since mice lacking IGF-II receptors die at birth (see for review). flovent inhaler

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Differential Distribution of Binding Sites: DISCUSSION(7)

IGF-II is important in early placentation, growth, and development of the fetal-placental unit and in transport across fetal membranes in humans. However, its synthesis does not seem to be correlated only with the mitogenic activity of cells, but also with invasive trophoblastic processes in the first trimester of gestation. Some have found mRNAs for IGF-II in the syncytiotrophoblast, but others have not ; IGF-II peptide was found in full-term syncytiotrophoblast, but cells containing its mRNA are not always identical with the cells that contain the protein, because immunoreactive cells may have taken up IGF-II secreted by neighboring cells. buy ortho tri-cyclen online

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Differential Distribution of Binding Sites: DISCUSSION(6)

DISCUSSION(6)

Two of the three sets of binding sites for 125I-IGF-II on the two trophoblast membranes are links in the chain of a regulation system. One is the insulin system. In the first trimester of gestation, the fetal-placental insulin system is under the mother’s control; it moves to the control of the fetus at the end of gestation when, interestingly, there are more receptors on the membrane that bathes the maternal blood in the intervillous space than on the membrane that faces the fetus. buy ortho tri-cyclen

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Differential Distribution of Binding Sites: DISCUSSION(5)

The insulin and insulin-like growth factors, which have many actions in the placenta, may be derived from the fetal circulation, the maternal circulation, and/or the trophoblastic cells. Their activities are potentiated by transport proteins through receptors they activate. The binding of 125I-IGF-II to the two purified membranes supports the notion that the membranes are polarized for these receptors (Fig. 3). This type of differential distribution has also been reported for another cytokine, epidermal growth factor, for which there were found to be 40% more receptors on microvillous membranes than on basal plasma membrane. Buy Asthma Inhalers Online

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Differential Distribution of Binding Sites: DISCUSSION(4)

The high molecular mass band designated as В is always present with this F band on SDS-PAGE and has the same reactivity toward unlabeled competitors as the 130-kDa F band. This band is therefore an a-a dimer with two IGF-I-receptor a subunits. The third set of 125I-IGF-II-binding sites (E) migrates in the 135-kDa molecular mass region. levitra super active plus

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Differential Distribution of Binding Sites: DISCUSSION(3)

DISCUSSION(3)

The maximal binding of 125I-IGF-II to the basal plasma membranes is similar to that found earlier for the muscle layer of the stem villi vessels of the human term placenta , but significantly (p < 0.0001) smaller than that for the microvillous membranes. These findings are corroborated by cross-linking experiments showing that the total 125I-IGF-II bound to microvillous membranes is 1.5 times that of 125I-IGF-II bound to basal plasma membranes.

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Differential Distribution of Binding Sites: DISCUSSION(2)

These values are similar to those reported for rat total placental membranes , ovine total placental membranes , and other tissues. There is one set of a subunits of the type 1 IGF receptor on basal plasma membranes that accounts for 30% of the total 125I-IGF-II bound. As reported by others for membranes of intact cells, the affinity of this type 1 IGF receptor for IGF-I is 0.2-1.0 nM, while its affinity for IGF-II is 2- to 15-fold lower. Consequently, the 125I-IGF-II bound by this receptor on the basal plasma membranes may account for the “pseudo-negative” cooperativity among 125-IGF-II-binding sites because there are in fact, two binding sites. These a subunits of the type 1 IGF receptor may have two origins, although our PAGE method does not distinguish between them: the real type 1 IGF receptor and a population of hybrid receptors. Populations of IGF-I/insulin hybrid receptors have been found in several human cell lines and total placental membranes. These chimeras consist of an a-(3 dimer of the IGF receptor linked to a-0 dimer of the insulin receptor, and their ligand properties resemble those of the type 1 IGF receptor. birth control pills

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Differential Distribution of Binding Sites: DISCUSSION(1)

DISCUSSION(1)

This report describes the J25I-IGF-II-binding sites in the trophoblast of the human full-term placenta, as well as their distribution over the brush-border microvillous and basal plasma membranes, which are the maternal-placental and the fetal-placental frontiers of the trophoblast. Both membranes possess type 1 and type 2 IGF receptors and insulin receptors, but the number and distributions of the receptors on the membranes differ. ventolin inhaler

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Differential Distribution of Binding Sites: RESULTS(5)

2Sl-lnsulin. 125I-Insulin bound mainly to two bands of microvillous membrane protein (data not shown). The less intense band (A) had a molecular mass higher than 250 kDa, and the label was displaced by IGF-I. The most intense band migrated at 135 kDa (E) and was displaced only by insulin; neither IGF-I nor IGF-II displaced the labeled ligand. Labeled insulin incubated with basal plasma membranes was bound essentially to two bands (Fig. 6). The slower band (A) had a molecular mass higher than the band (molecular mass > 250 kDa) to which the 125I-insulin bound. It was displaced by neither IGF-I nor IGF-II, but was completely displaced by insulin. However, this electrophoretic profile also occurred when a high membrane protein concentration was used in the reaction mixture. The second labeled band had a molecular mass of 135 kDa (E) and was not displaced by IGF-I or IGF-II, only by unlabeled insulin.

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Differential Distribution of Binding Sites: RESULTS(4)

RESULTS(4)

25/-/GF-/. 125I-IGF-I was bound mainly to three bands of microvillous membrane protein (Fig. 5). The labeled ligand that bound to a slow-moving molecule of molecular mass higher than 250 kDa (B) was displaced by unlabeled IGFI. The main labeled band migrated in the 135-kDa (E) region and was displaced by 200 |xg IGF-I (it became only faintly labeled). The third (130 kDa) band (F) was less intense than the 135-kDa one, but unlabeled competitors affected it in the same way as they did the 135-kDa band. Continue reading