Characterization of the receptor for epidermal growth factor-urogastrone in human placenta membranes

Epidermal Growth Factor (EGF) in the Human Placental Infection with Trypanosoma cruzi

Maternal infection of Trypanosoma cruzi is associated with premature births, abortions and placentitis. A decrease in EGF levels has been suggested to occur in animals infected by T. cruzi, but there is no research about the levels of EGF in human patients with Chagas' disease. We evaluated serum EGF levels in pregnant women with and without the disease, and with immunological methods detected EGF receptors and EGF in both groups of placentae and in cultures of normal placental villi with and without parasites. PLAP in placentae from those women was also immunologically detected, since EGF can induce the release of PLAP from the trophoblast surface and PLAP is suggested to be a receptor allowing parasite invasion of the placenta. Plasma from women with Chagas' disease contained lower level of EGF when compared to plasma of healthy women. Placentae from women with Chagas' disease showed lower PLAP expression but same level of detectable EGF receptors and EGF when compared with placentae from women without the disease. Culture with parasites did not reduce EGFr level. Results suggest a lower availability of EGF in women with Chagas' disease, which could explain several malfunctions of the placenta associated with maternal Chagas' disease.

The effect of epidermal growth factor on prostaglandin synthesis of oestrogenized rat uterus is mediated by nitric oxide

We examined the possible relationship between cytokines, nitric oxide and prostaglandins (PGs) in the estrogenized rat uterus. Results indicate that epidermal growth factor (EGF) enhances the synthesis of prostaglandins in estrogenized rat uteri and induces the augmentation of nitric oxide (NO) production in this tissue by stimulating iNOS. While the effect of EGF is abolished by L-NMMA, an NO antagonist, the NS-398, a cyclooxygenase-II (COX-II) inhibitor, prevents the augmentation of prostanoids induced by EGF. These results suggest that there is an interaction among EGF, NO and PGs and that in this interrelationship are involved COX-II and iNOS. This mechanism might be important during implantation and labor.

The role of the placenta in fetal nutrition and growth

The placenta plays a key role in the nutrition of the fetus. It mediates the active transport of nutrients and metabolic wastes across the barrier separating maternal and fetal compartments, as well as modifying the composition of some nutrients through its own metabolic activity. The function of the placenta is essential to the growth of a healthy fetus; it is becoming apparent that the activities of the placenta are in turn modulated by signals originating from the fetus. Communication between placenta and fetus is especially critical in intrauterine growth retardation. The importance of the interaction of factors like insulin-like growth factor and epidermal growth factor with their receptors is becoming increasingly clear.

Effects of the anti-gastric secretory drugs IT-066 and omeprazole mitogenic activities in the gastric juice of the rat

BACKGROUND

Salivary epidermal growth factor (EGF) retains its biologic function in gastric juice and may play a physiologic role. Little is know, however, about the existence of mitogens other than EGF and the constitutional alterations of these factors in gastric juice by anti-secretagogues.

METHODS

The mitogenic activity was evaluated by measuring [3H]-thymidine incorporation, and the EGF contribution was determined by using a specific anti-rat EGF antibody. An H2-receptor antagonist (IT-066) and a proton pump inhibitor (omeprazole) were used to determine whether these drugs alter the relative composition of active mitogens in gastric juice.

RESULTS

Normal gastric juice significantly increased DNA synthesis. This activity was suppressed by antibody (87-88%). Both drugs increased EGF concentrations and activity dose-dependently IT-066 specifically increased total amount and activity of EGF. Approximately 50% of this activity was reduced by boiling or antibody.

CONCLUSION

The major mitogenic activity of normal rat gastric juice depends on EGF, and antisecretory drugs enhance the mitogenic activity by preserving and including intraluminal mitogens than EGF.

Inhibition of gastric mucosal mucin receptor by H. pylori lipopolysaccharide: effect of ebrotidine

1. H. pylori infection causes the loss of mucus coat continuity and its patchy appearance. Here, we present evidence that the bacterium, through its cell wall lipopolysaccharide, disrupts the interaction between mucin and its mucosal receptor, and that ebrotidine is capable of counteracting this process. 2. The receptor for mucin, isolated from the solubilized gastric epithelial cell membrane by affinity chromatography on Sepharose-bound wheat germ agglutinin, displayed a molecular weight of 97 kDa and exhibited specific affinity towards mucin-coated surface. 3. The mucin binding to the receptor was susceptible to the inhibitin by H. pylori lipopolysaccharide and reached a maximum of 91%. This effect of the lipopolysaccharide was counteracted by ebrotidine, which caused a dose-dependent relief of the lipopolysaccharide inhibitory effect with maximum restoration in mucin-receptor binding of 51% at 60 microliters/ml ebrotidine. 4. The results show that H. pylori, through its lipopolysaccharide, is capable of disrupting the integrity of mucus perimeter of gastric mucosal defense and that antiulcer agent, ebrotidine, counteracts this untoward effect.

Differential binding and internalization of insulin-like growth factor (IGF)-I in cultured human trophoblast and JEG-3 cells: possible modulatory effect of IGF binding proteins (BP)

The present study was undertaken to characterize and identify the insulin-like growth factor binding proteins (IGF BPs) secreted by placental cells and their possible modulatory effect on IGF-I binding to cell surface receptors. The experimental approach taken was comparative characterization of binding and internalization of IGF-I and its analog, [Gln(3), Ala(4), Tyr(15), Leu(16) (QAYL)]IGF-I, with reduced affinity for IGF BP, in two different placental cell culture models. One was human placental trophoblast in primary culture and the other, JEG-3 cells, a human choriocarcinoma cell line, representing placental trophoblasts. Binding of [(125)I]IGF-I in both trophoblast and JEG-3 cells was time and temperature dependent. At 37°C, the plateau of [(125)I]IGF-I binding to both the cells (1-2% specific binding per 10(5) cells) was reached by 40-60 min. At 4°C, the time required to reach the plateau in both cells was increased to ∼4h. The maximum binding of [(125)I]IGF-I to trophoblasts, however, was ∼2 times higher than at 37°C, whereas in JEG-3 cells binding remained the same. Internalization of [(125)I]IGF-I in trophoblast cells was low and temperature independent. At both 37 and 4°C, ≤30% of the total cell-associated [(125)I]IGF-I was internalized. In contrast, internalization of [(125)I]IGF-I in JEG-3 cells was rapid and temperature dependent. At 37°C, ≥60% of the total cell-associated [(125)]IGF-I was internalized by 40-60min. At 4°C, internalization was slow and did not exceed 10% of the total cell-associated radioactivity. Binding of [(125)I-QAYL]IGF-I to trophoblasts, in comparison to [(125)I]IGF-I, was significantly different. The binding was undetectable at 37°C and it was low at 4°C. In JEG-3 cells, however, the binding and internalization of [(125)I]-QAYL]IGF-I at both the temperatures were comparable to that of [(125)I]IGF-I. Further characterization of the two [(125)I]IGF-I bindings to the different placental cells was achieved by binding competition studies using unlabelled IGF-I, [QAYL]IGF-I and [Leu]IGF-I, another analog of IGF-I, [Leu(24), 1-62]IGF-I with reduced affinity for the IGF-I receptor, and α-IR3, a monoclonal antibody to the IGF-I receptor. The different potencies of IGF-I and its analogs, and α-IR3 in competing binding of two [(125)I]IGF-Is in the different cells suggested that binding of IGF-I to JEG-3 cells was predominantly to IGF-I receptor, whereas to trophoblast cells it was to IGF BP. This was confirmed by affinity cross-linking studies. The major affinity cross-linked [(125)I]IGF-I complex in trophoblast cells was shown to be a protein of Mr. ∼43 kDa, corresponding to IGF BP-3. In JEG-3 cells, the major cross-linked [(125)I]IGF-I and-[QAYL]IGF-I complexes were proteins of Mr ∼130 kDa and >260 kDa, corresponding to the monomeric and multimeric forms of IGF-I receptor. The ∼43 kDa complex in trophoblast was confirmed to be IGF BP-3 by identification of the characteristics of the IGF BP secreted by trophoblast by Western ligand and immunoblots of the conditioned media. JEG-3 cells did not secrete IGF BP. In conclusion, the membrane associated IGF BP-3 in trophoblast cells, shown here, imply anin vivo modulatory effect of membrane bound IGF BP-3 on IGF-I action in placenta. JEG-3 cells, not secreting IGF-BP, offer an attractive model to study the interactive mechanism of IGF-I and IGF BP-3 actions on the placenta.

A novel Leydig cell cDNA-derived protein is a relaxin-like factor

According to Burkhardt et al. (Burkhardt, E., Adham, I. M., Brosig, B., Gastmann, A., Mattei, M. G., and Engel, W. (1994) Genomics 20, 13-19) Leydig cells contain the message for a protein of the insulin/relaxin family which was named Leydig cell insulin-like protein (LEY I-L). We have synthesized the human LEY I-L according to the amino acid sequence deduced from the published cDNA structure and obtained preliminary results concerning its potential target organs and its biological activity. Leydig cell insulin-like protein binds specifically to crude membrane preparations of mouse uterus and brain and shows cross-reactivity with the relaxin receptor, but not the insulin receptor. On the basis of these observations, together with the results of earlier structure-function considerations, we suggest that the new protein is a relaxin-like factor. By itself the new factor shows no obvious effect, but when given together with relaxin it significantly enhances relaxin-mediated widening of the mouse symphysis pubis.

Epidermal growth factor binding by membranes of human renal cell carcinomas: establishment of an epidermal growth factor receptor assay for clinical use

In order to quantitate epidermal growth factor receptors (EGFR) in human renal cell carcinoma (RCC) tissues, the binding of isotope-labeled epidermal growth factor (125I-EGF) to pooled membrane samples from human RCC was studied. Specific EGF binding to membranes at 4 degrees C reached a plateau after 2 h of incubation and remained constant up to 8 h; specific binding at 25 degrees C reached a plateau after 30 min of incubation, then decreased gradually. 125I-EGF binding to the membrane was displaced by both EGF and transforming growth factor-alpha, but not by insulin and basic fibroblast growth factor. Scatchard analysis of the specific EGF binding generated a straight line, indicating a single class of binding sites for EGF, with a dissociation constant (Kd) of 21.1 x 10(-10) M and a maximum number of binding sites of 57.2 fmol/mg membrane protein. When the protein concentration in the incubation medium was adjusted from 0.71 mg/ml to 2.84 mg/ml, Scatchard analysis revealed identical Kd values, and the maximum number of binding sites was proportional to the protein concentration. These results demonstrate the presence of EGFR on RCC membranes and indicate that these receptors can be studied quantitatively.

Inhibition of gastric mucosal mucin receptor by Helicobacter pylori lipopolysaccharide: effect of sulglycotide

1. A receptor for mucin was isolated from the solubilized gastric epithelial cell membrane by affinity chromatography on Sepharose-bound wheat germ agglutinin. 2. The receptor protein displayed a molecular weight of 97 kDa and exhibited specific affinity towards mucin-coated surfaces. The optimum for mucin binding occurred at 60-100 micrograms/ml, while the values for the receptor were 2.0-3.1 micrograms/ml. 3. The mucin binding to the receptor was susceptible to Helicobacter pylori lipopolysaccharide which caused maximum inhibition of 91% at 30 mu/ml. This inhibitory effect of the lipopolysaccharide was abolished by a gastroprotective agent, sulglycotide. 4. The effect of sulglycotide was dose dependent and at 50 micrograms/ml produced a 94% restoration in receptor-mucin binding. Furthermore, sulglycotide was also capable of enhancing (97%) the mucin binding to its receptor in the absence of the lipopolysaccharide. 5. The results demonstrate that H. pylori through its lipopolysaccharide interferes in the interaction of mucin with gastric epithelial surfaces and that a gastroprotective agent, sulglycotide, counteracts this effect, and hence is capable of preventing the loss of mucin coat continuity occurring with H. pylori infection.

Acidification reveals a greater number of epidermal growth factor receptors in human placental and breast cancer membranes

The detection of epidermal growth factor receptors (EGFR) has been proposed as a prognostic factor in different kinds of neoplastic diseases. In this study, we have compared different conditions of EGFR assay, in human placental membranes, in order to establish the best conditions for the routine use of EGFR assay in clinical laboratories. Three kinds of membrane treatment (non-treated, preincubated at 37 degrees C for 30 min, or acid treated at pH 3.0 for 3 min at 0 degrees C), two different separation conditions (hydroxylapatite and centrifugation), two different incubation times (30 min at 37 degrees C and overnight at 18 degrees C) and the effect of proteolytic enzyme inhibitors have been investigated. Preincubated or acid treated membranes showed a two- and three-fold increase of the number of receptors, respectively, as compared with non-treated membranes. In the case of acid pretreated membranes a second, low affinity, site became apparent. Both separation methods gave similar results. The addition of aprotinin had an effect only during long incubation conditions. Freezing of membranes in liquid nitrogen, followed by storage at -80 degrees C for 48 h, resulted in three different patterns. No change was observed in non-treated membranes. Preincubated samples showed a significant decrease both in the number and the affinity of detected EGFR. Acid treated membranes showed a decrease of the affinity of high affinity EGFR with no modification of their number. It is proposed that acid pretreatment, freshly prepared membranes, addition of aprotinin and the use of hydroxylapatite, for the separation of bound and free radiolabelled EGF, should be used in order to standardize the EGFR assay in clinical laboratories. Using these conditions, we were able to detect a significantly higher number of EGFR in 6/29 cases of human breast cancer specimens.

Alteration of epidermal growth factor receptor in placental membranes of smokers: relationship with intrauterine growth retardation

OBJECTIVE

The study of a possible alteration of epidermal growth factor receptor in placental membranes of smokers was performed.

STUDY DESIGN

We investigated the binding capacity and the autophosphorylation of epidermal growth factor receptor in membranes of 33 term placentas from smokers and nonsmokers with appropriate-for-gestational-age or small-for-gestational-age babies.

RESULTS

The binding capacity of epidermal growth factor receptor was similar in the four subgroups of placental membranes. In contrast, epidermal growth factor receptor autophosphorylation was impaired in the membranes from smokers relative to those from nonsmokers. This decrease was significant (p < 0.001) in the membranes from smokers with small-for-gestational-age babies. Insulin receptor phosphorylation was similar in the four groups.

CONCLUSION

Intrauterine growth retardation in women who smoke is associated with an alteration of placental epidermal growth factor receptor bioactivity and suggests that the regulatory role of epidermal growth factor in placental growth and differentiation is defective in this setting.

Epidermal growth factor receptor levels increase but epidermal growth factor receptor ligand levels decrease in mouse mammary tumors during progression from hormone dependence to hormone independence

Twenty-six serially transplanted Grunder (GR) strain mouse mammary tumors were analyzed for epidermal growth factor receptor (EGFR) and EGFR-ligand levels, in addition to steroid hormone receptors (estrogen receptor, ER, progesterone receptor, PgR). In concordance with earlier studies, hormone dependent (HD) and hormone responsive (HR) tumors were found to be positive for both ER and PgR, whereas hormone independent (HI) tumors contained only 30% of the ER concentration that was found in the HD tumors. PgR was undetectable in HI tumors. HI tumors contained 2.5 to 3-fold higher EGFR levels than HD/HR tumors, an observation which shows remarkable concordance with studies on EGFR in human breast cancer. On the other hand, the level of EGFR-ligand(s) was positively associated with ER levels and was three-fold higher in HD/HR tumors than in HI tumors. The low EGFR in HD/HR tumors relative to HI tumors may be the result of downregulation by EGFR ligands produced under ER control. During progression to hormone independence this downregulation of EGFR is then abolished in absence of ER. The increase in EGFR may therefore be a secondary effect rather than a key event in the progression to hormone independence in this mouse mammary tumor model.

Increase in epidermal growth factor receptor and its messenger ribonucleic acid levels with differentiation of human trophoblast cells in culture

Epidermal growth factor receptor (EGFR) expression was studied during the differentiation of human trophoblast cells in culture. In vitro, intravillous mononuclear cytotrophoblasts aggregate and fuse within 24 h to form a syncytium. This morphological differentiation was associated with a significant twofold increase in specific 125I-EGF binding capacity (P < 0.01). Scatchard analyses showed an apparent rise in the number of high-affinity binding sites (0.33 +/- 0.04 and 0.63 +/- 0.07 pmol/mg protein at 24 and 48 h, respectively), with no change in their affinity (1.34 and 1.42 x 10(-10) mol/L). Affinity labeling of 125I-EGF in cultured trophoblast cells followed by SDS-PAGE and autoradiography revealed a band of 175 KDa corresponding to EGFR, the intensity of which increased with the time in culture. EGF-dependent phosphorylation of membrane proteins from cultured trophoblast cells revealed major phosphorylated proteins of 170 KDa (EGFR) and 35 KDa, which were both increased at 48 h, indicating a rise in EGFR-kinase activity during syncytium formation. Northern blot analysis of EGFR-mRNA, followed by hybridization with a 32P-cDNA probe for EGFR, revealed an increase in EGFR gene expression in syncytiotrophoblasts, as compared to cytotrophoblasts. Thus, the increase in bioactive EGFR observed during the differentiation of trophoblast cells was due to an increase in their synthesis. Cultured trophoblast cells are therefore a good model of spontaneous up-regulation of EGFR expression with cell differentiation.

Localization of epidermal growth factor/transforming growth factor-alpha receptor in the human gastric mucosa. An immunohistochemical and in situ hybridization study

Current evidence indicates that epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) play a pivotal role in the maintenance of gastric mucosal integrity, via binding to a common cell-surface receptor (EGF/TGF-alpha receptor). We examined the distribution and cellular sites of synthesis of EGF/TGF-alpha receptor in normal human gastric mucosa by immunohistochemical and in situ hybridization techniques. Intense EGF/TGF-alpha receptor immunoreactivity was observed in the basal cytoplasm and along basolateral membranes of mucus neck cells, foveolar columnar cells, and surface epithelial cells facing the gastric lumen. Parietal cells and mucus-secreting pyloric gland cells displayed a distinct basolateral immunostaining, whereas the luminal membrane was unstained. Immunoreactivity was also noted in spindle-shaped cells of the lamina propria and in smooth muscle cells of the muscularis mucosae and muscularis propria. In situ hybridization revealed EGF/TGF-alpha receptor RNA transcripts in all cell types displaying positive immunoreaction. These results suggest a physiological role for EGF/TGF-alpha in the regulation of multiple gastric functions. The receptor distribution at the luminal aspect of the gastric mucosa provides the anatomical basis for a possible interaction of gastric juice EGF (or TGF-alpha) with cells of the mucosal surface, whereas the expression of EGF/TGF-alpha receptor in cells which are not in direct contact with the gastric lumen is consistent with blood-mediated or paracrine/autocrine mechanisms of EGF/TGF-alpha action on these cells.

Activation of dihydropyridine-sensitive parotid salivary gland calcium channels by epidermal growth factor

The calcium channel complex of the parotid was isolated from solubilized acinar-cell membranes by affinity chromatography on wheatgerm agglutinin. The channel, after labelling the calcium antagonist-receptor site with [3H]-PN200-100, was reconstituted into phosphatidylcholine vesicles that exhibited active 45Ca2+ uptake. This uptake was independent of sodium and potassium gradients, indicating its electroneutrality. The channels responded in a dose-dependent manner to the dihydropyridine calcium antagonist, PN200-110, which at 0.4 microM exerted a maximal inhibitory effect of 75% on 45Ca2+ uptake; a 46% enhancement in 45Ca2+ uptake occurred with a specific calcium-channel activator, BAY K8644. On epidermal growth-factor (EGF) binding in the presence of ATP, there was an increase in tyrosine phosphorylation of 55 and 170 kDa calcium-channel proteins. Such phosphorylated channels, after reconstitution into vesicles, displayed a 61% greater 45Ca2+ uptake, indicating the involvement of tyrosine kinase in EGF-dependent activation of the calcium channel. The results point towards the importance of EGF in the regulation of calcium homeostasis in salivary gland.

Benzo[a]pyrene and nicotine impair epidermal growth factor mediated cellular functions of buccal mucosa

This study investigated the effect of two major ingredients in cigarette smoke, benzo[a]pyrene (BP) and nicotine, on epidermal growth factor (EGF) receptor binding and EGF-mediated cellular functions in rat buccal mucosa. Rat buccal tissue was incubated in DMEM in the absence (control) and presence of 10 microM BP or nicotine for 2.5 h at 25 degrees C. There were no significant differences in [125I]EGF binding to the buccal mucosal membranes between the control and treatment groups. Protein tyrosine kinase assay showed that EGF stimulated phosphorylation of a 170-kDa protein band in the controls, but not in the BP- and nicotine-treated samples. The basal [3H]thymidine incorporations were not significantly different between the groups. Nevertheless, addition of 5 nM EGF increased [3H]thymidine incorporation by 22% in the control, but not in the BP- or nicotine-treated group. The results demonstrate that BP and nicotine change the buccal mucosal functions associated with alteration of EGF receptor.

Signal transmission by epidermal growth factor receptor: coincidence of activation and dimerization

Dimerization of epidermal growth factor receptor dissolved in a solution of nonionic detergent was followed with a resolution of 1 min by quantitative cross-linking with glutaraldehyde. Upon addition of epidermal growth factor to the solution, the initially monomeric protein dimerized in a reaction that was second-order in the concentration of receptor. A second-order rate constant, on the basis of enzymatic activity as a measure of the concentration of functional receptor, was calculated from time courses of dimerization at various initial concentrations of receptor. The activation of the protein tyrosine kinase of the receptor was monitored directly under the same conditions with an exogenous substrate. The increase in tyrosine kinase activity displayed kinetics that were also second-order in the concentration of receptor. A second-order rate constant for the activation of the tyrosine kinase could be calculated from the time courses. The second-order rate constant for the activation of the tyrosine kinase by epidermal growth factor was indistinguishable from the second-order rate constant for the dimerization induced by epidermal growth factor. Therefore, dimerization of epidermal growth factor receptor and activation of its tyrosine kinase are coincident events, both initiated by the binding of epidermal growth factor.

Ethanol-induced structural and functional alterations of epidermal growth factor receptor in buccal mucosa

1. Ethanol treatment caused a 47% decrease in [125I]EGF binding to the membrane preparations of buccal mucosa resulting from the decrease of binding sites rather than the affinity of high affinity receptor. 2. The immunoblot revealed a protein band of 170 kDa in the control sample, while a barely detectable 200 kDa protein was observed in the ethanol-treated sample. 3. Protein kinase assays using [32P]ATP as probe showed an EGF-stimulated phosphorylation band of 170 kDa in the control but not in ethanol-treated sample. 4. Ethanol did not change the basal incorporation of [3H]thymidine and [35S]methionine, but caused a 38% and 57% decrease of EGF-stimulated thymidine and methionine incorporation, respectively. 5. The data suggest that EtOH decreases EGF receptor binding through modification of the receptor molecule, thereby impairing receptor kinase activity and its physiological function.

Growth factors in the uterus: steroidal regulation and biological actions

Rapid progress has been made within the last 5-6 years in characterizing polypeptide growth factors in uterine tissues and fluids. There is convincing evidence that their synthesis and/or secretion is regulated by steroid hormones. The possibility that these growth factors play a central role in growth and development of the uterus or placenta is suggested by the presence of their receptors on uterine or placental cells and their stimulatory effects on these cells in vitro. Since growth factors interact synergistically and also have non-mitogenic functions, the presence of a variety of these factors in the uterus suggests that they probably regulate various aspects of uterine function through complex autocrine and paracine pathways. However, experimental models need to be designed that will permit a more detailed analysis of the actual role of these factors in utero. Fruitful approaches may be to administer neutralizing antibodies or blocking peptides so as to antagonize uterine growth factor action, or to develop appropriate transgenic animals. These and other lines of study should help us to understand the role of growth factors in development of the immature uterus, growth of the placenta or gravid uterus, repair and angiogenesis of the endometrium, and uterine pathology.

Characterization of a novel receptor in toad retina with dual specificity for insulin and insulin-like growth factor I

The biochemical properties of insulin receptors from toad retinal membranes were examined in an effort to gain insight into the role this receptor plays in the retina. Competition binding assays revealed that toad retinal membranes contained binding sites that displayed an equal affinity for insulin and insulin-like growth factor I (IGF-I). Affinity labeling of toad retinal membrane proteins with 125I-insulin resulted in the specific labeling of insulin receptor alpha-subunits of approximately 105 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of partially reduced (alpha beta-heterodimer) receptors affinity-labeled with 125I-insulin indicated the presence of a disulfide-linked beta-subunit of approximately 95 kDa. Endoglycosidase F digestion of the affinity-labeled alpha-subunits increased their mobility by reducing their apparent mass to approximately 83 kDa. This receptor was not detected by immunoblot analysis with a site-specific antipeptide antibody directed against residues 657-670 of the carboxy terminal of the human insulin receptor alpha-subunit, whereas this antibody did label insulin receptor alpha-subunits from pig, cow, rabbit, and chick retinas. In in vitro autophosphorylation assays insulin stimulated the tyrosine phosphorylation of toad retina insulin receptor beta-subunits. These data indicate that toad retinal insulin receptors have a heterotetrameric structure whose alpha-subunits are smaller than other previously reported neuronal insulin receptors. They further suggest that a single receptor may account for both the insulin and IGF-I binding activities associated with toad retinal membranes.

Characterization of epidermal growth factor binding to hepatic plasma membranes of rainbow trout (Oncorhynchus mykiss)

Epidermal growth factor (EGF) is a potent mitogen which exerts its effects through a transmembrane receptor located on target cells. Since little is known about EGF in nonmammalian animals, experiments were conducted to characterize the EGF receptor in rainbow trout hepatic cell membranes. The binding of mouse EGF with rainbow trout receptors was peptide-specific, saturable, reversible, and of high affinity. Optimal binding was observed at pH 7.2. Both monovalent and divalent cations augmented the specific binding of EGF, by a factor of two- to threefold over control values, but were not needed for binding to occur. Scatchard plot of the saturation data was curvilinear. Analysis of the data by kinetic methods indicated the curvilinear nature of the Scatchard plot was due to multiple receptor sites of differing affinity and not to site-to-site interactions. Rate constants for association (K11) were 9.38 X 10(8) M-1 * min-1 and 2.28 X 10(7) M-1 * min-1 for the high and low affinity sites, respectively. Rate constants for dissociation (K-1) were 2.03 X 10(-3) min-1 and 2.07 X 10(-1) min-1 for high and low affinity sites, respectively. The apparent dissociation constants determined from the rate constants for the high affinity (KD = 2.3 X 10(-11) M) and low affinity (KD = 9.1 X 10(-9) M) were in agreement with constants estimated by equilibrium methods. Maximum binding capacities were 13 fmol EGF bound/mg protein of protein and 270 fmol EGF bound/mg of protein for the high and low affinity receptor sites, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The membrane fraction of homogenized rat kidney contains an enzyme that releases epidermal growth factor from the kidney membranes

High levels of epidermal growth factor (EGF) are excreted in the urine and high levels of mRNA for the EGF-precursor have been demonstrated in the kidney. The EGF-precursor is a membrane bound peptide in the kidney, but little is known about the renal processing of the precursor. The present study shows that the membrane fraction of homogenized rat kidney contains an enzyme that releases immuno and receptor reactive EGF from the kidney membranes when incubated at 37 degrees C. Gel filtration shows that the EGF reactivity released from the membranes is similar to the EGF reactivity in rat urine. The EGF releasing enzyme is inhibited by the serine proteinase inhibitor aprotinin and by low temperatures (4 degrees C). The pH optimum of the reaction is pH 7.5-8.0.

Effects of maternally administered epidermal growth factor on placental permeability

Epidermal growth factor is a well-studied modulator of epithelial membrane structure and function. Mammalian placentas are a rich source of epidermal growth factor receptors, but the role of epidermal growth factor in placental pathophysiologic conditions is unclear. To determine whether epidermal growth factor could affect mechanisms of placental transfer, we used an in situ rat placental perfusion model. Fourteen Sprague-Dawley rats that were 20 days pregnant were randomized to epidermal growth factor or placebo during placental transport experiments. We chose ethylenediaminetetraacetate tagged with chromium 51 as a marker of placental permeability. Epidermal growth factor treatment led to a dramatic increase of maternofetal clearances of chromium 51-ethylenediaminetetraacetate. We conclude that maternally administered epidermal growth factor has a potent action on placental permeability.

Inhibition of gastric mucosal laminin receptor by Helicobacter pylori lipopolysaccharide

Laminin receptor was isolated from gastric epithelial cell membrane by the procedure involving membrane solubilization with octylglucoside followed by affinity chromatography on laminin-coupled Sepharose. The receptor protein, eluted from the matrix with cation-free EDTA buffer, yielded on SDS-PAGE a single 67kDa band. After radioiodination, the protein was incorporated into liposomes which displayed specific affinity toward the laminin-coated surface. The binding of liposomal receptor to the laminin-coated surface was inhibited by lipopolysaccharide from H.pylori. The inhibitory effect was proportional to the concentration of lipopolysaccharide up to 50 micrograms/ml at which point a 96% decrease in the receptor binding occurred. It is suggested that a similar process may account for the loss of mucosal integrity in the pathogenesis of H. pylori associated gastric disease.

Inhibition of bovine gingival laminin receptor by bacterial lipopolysaccharide

A laminin receptor was isolated from bovine gingival epithelial-cell membrane. After solubilization with octylglucoside, the receptor was subjected to affinity chromatography on laminin-coupled Sepharose and eluted with cation-free EDTA buffer yielding on SDS-PAGE a 67 kDa protein band. After radioiodination, the protein was incorporated into liposomes which displayed specific affinity towards laminin-coated surfaces, as well as to tooth cementum. The binding of receptor protein to cementum was inhibited by lipopolysaccharide from Bacteroides gingivalis. Preincubation of cementum with the lipopolysaccharide decreased the binding of the liposomal laminin-receptor preparation by 35.8%, while a 59.2% decrease in binding occurred when the lipopolysaccharide was preincubated with the receptor, suggesting that the lipopolysaccharide interfered with the laminin binding site on the receptor. The results demonstrate the existence of a specific gingival cell-surface laminin receptor, show that it is capable of binding to cementum, and provide evidence for the disruption of this process by bacterial lipopolysaccharide. This mechanism may account for the loss of gingival attachment in the pathogenesis of periodontal disease.

Identification of laminin receptor in gingival tissue and its interaction with tooth cementum laminin

1. A gingival epithelial cell surface receptor for laminin was isolated from bovine gingival tissue by affinity chromatography on laminin. 2. The protein bound by the affinity matrix from octylglucoside extracts of gingival membrane preparation eluted from the column with the cation-free buffer containing EDTA, and exhibited a mol. wt of 67 kDa. 3. The 67 kDa protein following radioiodination was incorporated into liposomes, which showed a specific affinity towards laminin-coated surfaces, as well as to the tooth cementum. 4. The results provide for the first time evidence for the existence of a gingival cell surface laminin receptor, and indicate that the maintenance of the cemento-epithelial junction involves the interaction between the cementum laminin and its receptor on gingival epithelium.

EGF receptor-binding activity in the urine of normal horses and horses affected by chronic laminitis

A heterologous radioreceptor binding assay (RRA) has been developed capable of detecting nanogram amounts of epidermal growth factor (EGF) receptor-binding activity in equine urine. The binding parameters of [125I]mEGF (murine EGF) to EGF receptors on equine plasma membranes are in good agreement with values from other EGF-RRA systems. The dissociation constant estimated from equilibrium methods (KD = 4 X 10(-10) M) is in reasonable agreement with that determined from the rate constants (KD = 6 X 10(-10) M) and is in good agreement with values determined in other species. The assay is specific for equine EGF (eEGF) receptor-binding activity and capable of detecting less than 0.34 nM eEGF receptor-binding activity in urine. Equine EGF receptor-binding activity in equine urine form adult horses varied widely between samples (8.5 +/- 6.5 nM). This variability was somewhat reduced when values were adjusted for dilutional effects using urine creatinine as an indicator (3.6 +/- 2.0 nanomoles/g creatinine). No significant differences were demonstrated between the means of EGF binding activity concentrations in clinically normal horses and horses affected by chronic laminitis.

Contribution of the C-terminal dipeptide of transforming growth factor-alpha to its activity: biochemical and pharmacologic profiles

We have used a matrix of biological (two distinct guinea-pig stomach contractile smooth muscle preparations) and biochemical (human placental membrane receptor binding and phosphorylation) assays to evaluate the activity profiles of epidermal growth factor-urogastrone (EGF-URO, mouse and human), transforming growth factor-alpha (TGF-alpha, human) and the TGF-alpha derivative lacking the C-terminal dipeptide, Leu49-Ala50, TGF-alpha-(1-48). In the longitudinal muscle (LM) bioassay, the relative potencies of the peptides were: EGF-URO greater than TGF-alpha greater than TGF-alpha-(1-48), with relative activity ratios (EC50S) of approximately 1:3:16. In the LM assay system, TGF-alpha-(1-48) was a partial agonist. In the circular muscle (CM) bioassay, the relative order of potencies was: TGF-alpha- greater than EGF-URO greater than TGF-alpha-(1-48), with EC50S of about 1:2:7. In the CM assay, all three peptides were full agonists, even though EGF-URO caused an intense desensitization of the tissue whereas TGF-alpha and TGF-alpha-(1-48) did not. The relative affinities of the peptides in the placenta membrane binding assay, EGF-URO greater than TGF-alpha greater than TGF-alpha-(1-48), were in good qualitative and quantitative agreement with the LM (but not the CM) bioassay, with relative KDS in the proportions of about 1:3:17. In the phosphorylation assay, using either the phosphorylated EGF-URO receptor or calpactin-II as an index of receptor kinase activation, the relative potencies of the peptides, EGF-URO greater than TGF-alpha greater than TGF-alpha-(1-48), were also qualitatively in accord with the relative potencies measured in the LM and ligand binding assays (but not in the CM preparation); however, quantitatively, the relative potency ratios (EC50S) observed in the phosphorylation assay (1:2:3) were somewhat out of keeping with the relative values observed in the LM and ligand binding assays. All three peptides were full agonists in the phosphorylation assay. Our data point to the importance of the C-terminal dipeptide, Leu49-Ala50 of TGF-alpha in terms of the binding affinity and intrinsic activity of this polypeptide; and our work provides further evidence for the distinct nature of the EGF-URO/TGF-alpha receptor system present in the CM bioassay preparation. The biological/biochemical activity profiles documented for the three polypeptides can serve as a basis for the further evaluation of other synthetic and naturally occurring members of the EGF-URO/TGF-alpha family of polypeptides.

Membrane vesicles of A431 cells contain one class of epidermal growth factor binding sites

Epidermoid carcinoma A431 cells exhibit two classes of epidermal growth factor (EGF) receptors as deduced from Scatchard analysis. Steady-state binding of EGF to isolated A431 membranes indicated, however, the presence of only one class of EGF binding sites. The apparent dissociation constant (Kd) of these sites was approx. 0.45 nM which is similar to that of the high-affinity receptor of intact A431 cells. These results suggest that the vesicle receptor population consists only of high-affinity receptors. However, further studies indicated that the binding sites were similar to the low-affinity class, since binding of EGF could be blocked entirely by 2E9, a monoclonal anti-EGF receptor antibody which is able to inhibit specifically EGF binding to low-affinity receptors in A431 cells. The difference in affinity of the receptors in membrane vesicles as compared to intact cells may be explained by differences in biophysical parameters such as diffusion-limited EGF binding and receptor distribution. Based upon these considerations, it is concluded that membrane vesicles of A431 cells contain one class of EGF receptors which are apparently identical to the low-affinity receptors of intact cells.

Epidermal growth factor receptors in rat placenta, amnion and yolk sac: characteristics of specific binding are dependent on gestational age

Studies of [125I]-EGF binding to the rat placenta, amnion and yolk sac were carried out on days 14, 17 and 20 of gestation. In the placenta EGF binding was detectable on all 3 days; in the amnion EGF binding was undetectably low on day 14 but was present on days 17 and 20, while in the yolk sac EGF binding was undetectably low on all 3 days. Although Scatchard analysis of EGF binding to placental tissue raised the possibility of high and low affinity receptors, a statistical analysis of the ligand binding data was consistent with the presence of only one type of EGF receptor. The overall affinity of the receptors did not change with stage of gestation. However, the concentration of EGF receptors was lower in placental tissue on day 17 than on days 14 or 20 of gestation; the receptor concentrations were similar on days 14 and 20. It is suggested that EGF binding to the placenta, amnion, and yolk sac may reflect the levels of cell proliferation in those tissues in the latter part of gestation.

Autoradiographic localization of binding sites for epidermal growth factor-urogastrone (EGF-URO) in coronary arteries

Previously published data have indicated that epidermal growth factor-urogastrone (EGF-URO) can regulate blood flow in vivo and can modulate vascular smooth muscle contractility in vitro. However, the exact location of the receptors responsible for this vascular action of EGF-URO has not been previously determined. In this report, employing in vitro autoradiography with 125I-labeled EGF-URO, we have documented the presence of specific EGF-URO binding sites in the tunica media of bovine and porcine coronary arteries. Our observations support the indirect evidence pointing to presence of EGF-URO receptors on the smooth muscle elements of arterial tissue. Our data also support further the hypothesis that EGF-URO and related growth factors (like TGF-alpha or PDGF) may play a role in normal and pathophysiological vascular function.

The receptor for epidermal growth factor is present in human fetal kidney, liver and lung

In animals a pharmacological doses of the growth-promoting peptide epidermal growth factor (EGF) has an effect on the growth and/or maturation of several organs such as the lung, the kidney, the liver and the gastrointestinal tract. Since EGF elicits its function via binding to specific cellular receptors the presence of these receptors predicts a possible physiological role for EGF and EGF agonists. We have studied the presence of the EGF-receptor on human fetal membrane preparations from the kidney, the liver, the lung and the placenta (gestational age 13-20 weeks). The 4 membrane preparations all bind labeled EGF thus allowing us to calculate the apparent affinity constant and the number of receptors present per mg of membrane protein. The apparent affinity constant (gestational age 13-20 weeks) varies between 0.5 and 3.5 X 10(9) mol-1, median 1.3 X 10(9) mol-1 (n = 40). No difference is observed for the 4 tissues examined, and no difference is found as a function of the gestational age. The number of receptors present per mg of membrane protein (gestational age 16-20 weeks) are (range and (median) 90-220 (130) fmol, n = 10 for the kidney, 80-480 (250) fmol, n = 9 for the liver, 90-690 (300) fmol, n = 10 for the lung, and 2100-4200 (3400) fmol, n = 7 for the placenta. Results for a fetus of gestational age 13 weeks show high values for kidney receptors (240 fmol) and lung receptors (800 fmol) and low values for the placenta receptors (410 fmol).

Minimal hydrolysis of epidermal growth factor by gastric fluid of preterm infants

Epidermal growth factor (EGF), present in high concentrations in milk, may play a role in growth of the gastrointestinal tract. Resistance to proteolytic degradation in the stomach is necessary if ingested EGF is to function within the gastrointestinal tract. Although EGF stability to low pH and proteases predicts gastric survival, the extent of digestion in the stomach remains to be defined. Consequently, we measured gastric degradation of 125I-human recombinant EGF in preterm infants with an in vitro method in which EGF was incubated at 37 degrees C with stomach fluid at pH 1.8, 3.2, and 5.8 followed by analysis of degradation products. As maximal acid proteolytic activity is present one hour after feeding in preterm infants, fluid was obtained at that time from 18 infants with a mean gestational age at birth of 30.4 (3.0) (SD) weeks and a postnatal age of 26.3 (12.7) days at sampling. Incubations for up to 60 minutes revealed minimal loss of trichloroacetic acid precipitable radioactivity, in contrast to the substantial hydrolysis of iodinated casein which occurred under the same conditions. Chromatography of reaction mixtures on Sephadex G-25 showed a single major peak of radioactivity which coeluted with EGF. Epidermal growth factor also retained greater than 75% of its ability to bind to anti-EGF affinity columns and placental membrane receptors after incubation with gastric fluid. These data support the concept of substantial gastric survival of ingested EGF in a potentially biologically active form in preterm infants.

Occurrence of epidermal growth factor receptors in human adnexal tumors and their prognostic value in advanced ovarian carcinomas

Ninety-eight different malignant adnexal tumors were analyzed for the presence of epidermal growth factor (EGF)-specific binding sites and binding parameters were calculated by Scatchard plot analysis [G. Scatchard, Ann. N.Y. Acad. Sci. 51, 660-672 (1949)]. Thirty-four biopsies were EGF receptor (EGF-R) positive with dissociation constants (KD) of 0.5-12 X 10(-9) M and binding capacities (Bmax) of 2-250 fmol/mg. One tumor had a KD of 60 X 10(-9) M and a Bmax of 1660 fmol/mg. The correlation of EGF-R status with clinical parameters showed no significant differences in primary, metastatic, or recurrent tumors, histological subtype, tumor differentiation, and tumor residual after primary surgery. As an inverse correlation, EGF-R-positive tumors are 39% and EGF-R-negative tumors 60% progesterone receptor positive. A response to chemotherapy was noticed in 50% of EGF-R-positive ovarian carcinomas with a mean survival time of patients of 28 months. The response rate of EGF-R negative ovarian carcinomas was 12% with a mean survival time of 16 months. Regarding the treatment schedule the major differences were noticed in the cis-platinum plus cyclophosphamide treatment group. These results suggest that the biology of ovarian carcinomas is influenced by growth factors and their receptors, which can be used as prognostic factors.

Luminal hydrolysis of recombinant human epidermal growth factor in the rat gastrointestinal tract: segmental and developmental differences

Epidermal growth factor (EGF), present in high concentrations in the milk of various species, is biologically active following oral administration to young animals. Although in vivo studies show gastrointestinal processing of dietary EGF during early postnatal development, the relative importance of luminal and mucosal digestion in such processing is undefined. To characterize the luminal metabolism of dietary EGF in the developing gastrointestinal tract, we incubated human recombinant 125I-EGF in vitro at 37 degrees with luminal fluid from the stomach and various segments of the small intestine of 12 day old suckling and 31 day old weanling rats and analyzed the resulting reaction products. The rate of EGF hydrolysis as determined by generation of acid soluble material was greater in weanling small intestine than in suckling, with maximal hydrolytic capacity observed in the mid-jejunum and ileum. Minimal hydrolysis was observed with stomach fluid from both age groups, and EGF retained its ability to elute as a single species on Sephadex G-25 columns and to bind to monospecific affinity columns and placental membrane receptors. Incubation with suckling small intestinal fluid produced little change in the chromatographic profile on Sephadex G-25, but a reduction in antibody and receptor binding was observed. In contrast, incubation with weanling small intestinal fluid yielded both a more pronounced loss of EGF-like material on G-25 columns and a greater reduction in receptor and antibody binding. We conclude that little luminal EGF degradation occurs in the rat stomach during the suckling and weanling periods, but that in the lumen of the small intestine breakdown increases during postnatal development.

Isolation of a major human placental substrate for the epidermal growth factor (urogastrone) receptor kinase: immunological cross-reactivity with transducin and sequence homology with lipocortin

Using as a starting material either a detergent extract or a protein fraction eluted from membranes with ethylene glycol bis (beta-aminoethyl ether)-N,N'-tetraacetic acid, we have isolated from human placental membranes a major substrate for the epidermal growth factor (urogastrone) receptor kinase (EGF kinase). The substrate was isolated both in an intact form, having a molecular mass of approximately 38-kDa (p38), and in a 35-kDa form (p35) representing a proteolytic cleavage product of p38. Both p38 and p35 cross-reacted with antibodies directed against bovine retinal transducin, but did not cross-react with antibodies directed against the 35-kDa beta subunit of human placental G-protein. Antisera directed against the placental EGF kinase substrate failed to react with either bovine or human placental src kinase substrate, p36. Conversely, antisera directed against p36 reacted only poorly with placental p38 or p35. Although p38 had a blocked amino terminus that precluded sequence analysis, p35 yielded an N-terminal sequence that was identical with residues 13-36 of human lipocortin. Our data clearly distinguish p38 from the previously described intestinal calcium binding protein calpactin I or p36 that is also a tyrosine kinase substrate, and our work points to a close relationship (if not identity) between p35 and a 35-kDa EGF receptor kinase substrate previously characterized in A431 cells. We conclude that p38 and p35, which very likely represent human placental lipocortin, may share only limited epitope homology with transducin alpha subunit; however, the possibility that p38, along with intestinal p36 and with a family of related calcium binding proteins, may, like transducin, play a role in receptor-mediated transmembrane signaling is discussed.

Monoclonal antibody GB17 recognizes human syncytiotrophoblast

A monoclonal antibody, GB17, was obtained from a hybridoma produced following murine immunization with isolated human term syncytiotrophoblastic microvilli. Immunohistological studies demonstrated the GB17 antigen to be present on syncytiotrophoblast of human term, first- and second trimester placenta, but not on human extravillous trophoblast or baboon placental trophoblast. Other normal adult human tissues and transformed cell lines tested were non-reactive with this antibody. Radio-iodinated term syncytiotrophoblastic microvillous protein was immunoprecipitated by GB17, and shown by sodium dodecyl sulfate--polyacrylamide gel electrophoresis to migrate as a single protein band at 175 kDa. The restricted tissue specificity suggests that the GB17 antigen could be useful for the development of a contragestational vaccine.

Activity of human, bovine and porcine platelet-derived growth factor in a radioreceptor assay with human placental membrane protein

Radioiodinated human platelet-derived growth factor (125I-PDGF), and unlabeled human (Hu), bovine (Bo), and porcine (Po) PDGF were used to study PDGF receptors in human term placental membrane preparations. The binding of 125I-Hu-PDGF was inhibited by unlabeled preparations. Half-maximal occupancy of the binding sites occurred at 7-9 nM of Hu-, Bo- or Po-PDGF. Scatchard analysis of the binding data indicated a single class of receptors having a Kd value of about 1.1-1.2 X 10(-10) M. Thus, the sensitive radioreceptor assay does not detect any species specificity of PDGF.

Purification of human epidermal growth factor (urogastrone) from urine

Human epidermal growth factor has been isolated from a concentrated chromatographic eluate of human urine. The purification method utilizes six chromatographic steps including adsorption to aminoethylcellulose (AE-11), gel filtration on Sephadex G-50, carboxymethylcellulose (CM-52) chromatography, ion-exchange HPLC and reverse-phase HPLC. The final product appears homogeneous and identical to pure gamma-urogastrone when analyzed by polyacrylamide gel electrophoresis and reverse-phase HPLC using two eluent systems. The yield of the method described above allowed the development of a sensitive radioimmunoassay system for this growth factor.

The effects of insulin-like growth factor-I and insulin on placental lactogen production by human term placental explants

The effects of insulin-like growth factor (IGF)-I and insulin on placental lactogen production (hPL) by term human placental explants were studied. The hPL content in medium and explant decreased rapidly after first 24 hours of culture. The decrease thereafter was gradual and reached a plateau by day 4 of culture. The decrease of HPL content in placental culture has previously been suggested being due to the depletion of a rapidly secreting preformed pool of hPL. Addition of IGF-I (0.1-10 micrograms/ml) and insulin (1-20 micrograms/ml) stimulated the decreased level of hPL in tissue and medium after 24 hours in culture. IGF-I was 10 times more potent than insulin in stimulating hPL. These findings suggest that IGF-I and insulin effects the production of hPL by placenta. The lower potency of insulin may indicate that the effect of insulin on hPL production is via IGF-I receptor.

Epidermal growth factor induces rapid, reversible aggregation of the purified epidermal growth factor receptor

Epidermal growth factor (EGF) receptor from A-431 cells was purified by affinity chromatography with monoclonal anti-receptor antibodies. The purified radiolabeled receptor was incubated with EGF and then analyzed by gel electrophoresis under nondenaturing conditions. In these gels, the EGF receptor migrates in two forms: a fast-migrating (low) form and an EGF-induced slow-migrating (high) form. On the basis of the various control and calibration experiments described, it is concluded that the low form represents the monomeric 170-kilodalton EGF receptor and the high form represents an EGF receptor dimer. The binding of EGF causes a rapid, temperature-sensitive dimerization of the EGF receptor. Receptor dimerization is fully reversible and involves saturable, noncovalent interactions that are stable at neutral pH and in nonionic detergents. Both the monomeric and dimeric forms of the receptor bind EGF and undergo self-phosphorylation. The dimeric form of the receptor may possess higher ligand binding affinity, and it seems to be phosphorylated earlier than the monomeric form following the addition of EGF and [gamma-32P]ATP. On the basis of these results, it is concluded that receptor oligomerization is an intrinsic property of the occupied EGF receptor and that it may play a role in the activation of the kinase function and the subsequent transmembrane signaling process.

Levels of epidermal growth factor binding in third-trimester and term human placentas: elevated binding in term placentas of male fetuses

Specific binding of iodine 125-labeled epidermal growth factor was measured in membrane homogenates of third-trimester and term human placentas of male and female fetuses. All placentas (n = 35) generated curvilinear Scatchard plots, and all placentas had similar equilibrium dissociation constants for both high-affinity (210 pmol/L) and low-affinity (830 pmol/L) binding sites. Mean maximum number of available binding sites of term placentas from male fetuses (330 +/- 110 fmol/mg protein; n = 11) was significantly higher (p less than 0.001) than that of female fetuses (170 +/- 80 fmol/mg protein, n = 13). Occupation of epidermal growth factor receptors by endogenous epidermal growth factor could not account for the difference in levels of epidermal growth factor binding. Kendall's rank order correlation test demonstrated a significant positive correlation of the gestational age in weeks with the maximum number of epidermal growth factor receptors in placentas from male fetuses (p less than 0.002; T = 0.527; n = 17) and female fetuses (p less than 0.01; T = 0.404; n = 18). These results indicate that there is a sexual dimorphism in the level of epidermal growth factor receptors in placentas of male and female fetuses during the third trimester and that the level of epidermal growth factor receptors increases during the third trimester for placentas of both male and female fetuses.

Does epidermal growth factor play a role in the action of sucralfate?

Epidermal growth factor (EGF) is a mitogenic peptide synthesized in the submandibular glands and released in saliva. EGF is able to prevent the development of gastrointestinal ulcers in the rat and to accelerate their healing. The present work was undertaken to examine whether Sucralfate acts via the effector system of EGF. We conclude that Sucralfate does not change the binding of EGF to its receptor, but it is able to bind EGF in a pH dependent manner and at pH below 4.5 virtually all EGF is bound to Sucralfate. In vivo studies in rats with acid-induced gastric ulcers show that sucralfate carries EGF to the ulcer, and that EGF is available for a longer period of time (3 hours) when EGF and Sucralfate are is given together than when EGF is given alone.