Transforming growth factor-α and other growth factors stimulate cell division in olfactory epithelium in vitro

The rate of cell division in olfactory epithelium (OE) is upregulated by ablation of the olfactory bulb (Carr and Farbman, 1992), or downregulated by occlusion of a naris. We used an organ culture assay of fetal rat olfactory mucosa to study regulation of the mitotic rate. Addition of any one of three members of the epidermal growth factor (EGF) family—EGF, transforming growth factor-α (TGF-α), or amphiregulin (AR)—to a serum-free culture medium resulted in a two- to threefold increase in the number of dividing OE cells. TGF-α elicited a maximal response in a dose of 100–200 pM culture medium and was 2 orders of magnitude more potent than the other EGF family members. Addition of TGF-β1, TGF-β2, insulinlike growth factor-1 or platelet-derived growth factor to the culture medium had slightly less effect than EGF or AR, in about the same molar dose range; addition of nerve growth factor had virtually no net effect on cell division. Immunohistochemistry on adult rat OE showed that basal cells, supporting cells, and acinar cells of Bowman's glands were immunoreactive with antibody to TGF-α but not with antibody to EGF. Most growth factors upregulated division of both olfactory neuron progenitors and supporting cells. The data suggest that several growth factors, most prominently TGF-α, may participate in the mitotic regulation of OE. © 1996 John Wiley & Sons, Inc.     

Epidermal growth factor inhibits morphogenesis and cell differentiation in cultured mouse embryonic teeth

Although local epithelial-mesenchymal tissue interactions which are presumably mediated by extracellular matrix molecules are important regulators of tooth morphogenesis and differentiation, our studies have indicated that these developmental processes also depend on circulating molecules. The iron-carrying serum protein transferrin is necessary for the early morphogenesis of mouse tooth in organ culture (A-M. Partanen, I. Thesleff, and P. Ekblom, 1984, Differentiation 27, 59-66). In the present study we have examined the effects of other growth factors on mouse tooth germs grown in a chemically defined medium containing transferrin. Fibroblast growth factor and platelet derived growth factor had no detectable effects but epidermal growth factor (EGF) inhibited dramatically the morphogenesis of teeth, and prevented odontoblast and ameloblast cell differentiation. EGF stimulated cell proliferation in the explants measured as [3H]thymidine incorporation in DNA. However, when the distribution of dividing cells was visualized in autoradiographs, it was observed that cell proliferation was stimulated in the dental epithelium but was inhibited in the dental mesenchyme. The inhibition of cell proliferation in the dental mesenchyme apparently caused the inhibition of morphogenesis. We do not know whether the dental epithelium or mesenchyme was the primary target for the action of EGF in the inhibition of morphogenesis. It is, however, apparent that the response of the dental mesenchymal cells to EGF (inhibition of proliferation) is regulated by their local environment, since EGF enhanced proliferation when these cells were disaggregated and cultured as monolayers. This indicates that the organ culture system where the various embryonic cell lineages are maintained in their original environment corresponds better to the in vivo situation when the roles of exogenous growth factors during development are examined.     

Synergistic influence of epidermal growth factor, insulin and transferrin on human fetal kidney in culture

In human fetal kidneys (15-21 weeks of gestation) maintained in serum-free organ culture, protein synthesis remained relatively constant, but DNA synthesis decreased dramatically after 2 days. The addition of transferrin alone had no influence, but insulin and epidermal growth factor (EGF) both significantly stimulated DNA and protein synthesis. When supplemented in combination, transferrin strongly potentiated the insulin effect and after 5 days of culture DNA synthesis was practically restored to values observed in control uncultured renal explants (day 0). When EGF, a potent mitogen, was added as a third factor, the stimulating effectiveness of the (insulin plus transferrin) combination was significantly reduced. However, EGF had no such inhibiting influence on protein synthesis. Differentiation of brush border membranes, as evaluated by hydrolase activities, was not importantly induced nor retarded by any of the three factors supplemented either alone or in combination. The present results indicate that the individual effects of the three factors are not additive, but suggest that they rather act synergistically through a complex mechanism of receptor cross-talk. In our laboratory, there is convincing indication that the response of fetal organs varies according to age, proliferative state of tissues as well as stage of differentiation.     

The effect of choleragen and epidermal growth factor on proliferation and maturation in vitro of human ectocervical cells

Summary The role of choleragen (CT) and epidermal growth factor (EGF) has been examined in relation to the control of growth and differentiation of adult human cervical epithelial (HCE) cells derived from the ectocervix. Cervical biopsies derived from hysterectomy specimens were trypsin disaggregated and HCE cells were plated at 5×10³/cm² in the presence of 2×10⁴/cm² lethally irradiated Swiss 3T3 fibroblasts. Cultures were grown in Liebovitz medium supplemented with 10% fetal bovine serum and hydrocortisone. Epidermal growth factor at 10 ng/ml and choleragen at 10⁻¹⁰ M were added to cultures either singly or in combination. DNA replication in these cultures was measured autoradiographically after exposing cells to tritiated thymidine for 2 h. Differentiation was assessed histochemically by determining glycogen accumulation using the periodic acid Schiff technique. Choleragen increased colony plating efficiency by at least a factor of two but had no effect on colony size Epidermal growth factor did not increase plating efficiency but did increase colony size. In EGF treated colonies DNA replication occurred throughout the colony compared to CT treated colonies in which replication was restricted to the periphery. In the absence of EGF, population doublings achieved in culture did not exceed 32 and glycogen accumulation was evident in cells early in culture life. Colonies treated with EGF exhibited glycogen accumulation late in culture life and the EGF treated cells achieved at least 50 population doublings in culture. The results are discussed in relation to the role of EGF and choleragen on cell differentiation.     

Epidermal growth factor (EGF) influences DNA synthesis in human fetal kidneys maturing in serum-free organ culture

Human fetal kidney explants (13-17 weeks of gestation) were maintained in serum-free organ culture. The influence of epidermal growth factor (EGF) was determined after 2 and 5 days by evaluating DNA and protein synthesis as well as the activities of five brush border hydrolases. During the studied period the overall morphology was preserved and the analysed parameters remained constant. Only DNA synthesis decreased after 2 days. The addition of EGF to the medium did not change any of the cell activities, except DNA synthesis. In fact, the incorporation of [3H]thymidine was significantly stimulated by 105% in 5-day explants cultured in the presence of the growth factor. These results indicate that EGF directly influences proliferation but not maturation of brush border enzymes in fetal human kidneys in culture.     

Involution of the female Mullerian duct of the fetal rat in the organ-culture assay for the detection of Mullerian Inhibiting Substance

The study of Mullerian Inhibiting Substance (MIS) has been made possible because of the organ-culture bioassay devised by Picon ('69) for detecting MIS in vitro. We have studied the degeneration of the female Mullerian duct of the rat fetus, the target tissue of the assay, with electron microscopy. We have observed that the involution of the female Mullerian duct in the organ-culture assay follows a pattern of degeneration similar to the normal involution of the male Mullerian duct under the influence of MIS from the fetal testis (Price et al., '77). This involution involves alterations in the duct epithelium subsequent to a response of the mesenchyme surrounding the duct. The degeneration of a specific organ system under the direct influence of a specific factor, Mullerian Inhibiting Substance, represents an example of "programmed cell death."     

Effects and interactions of epidermal growth factor, insulin, hydrocortisone, and estradiol on the cloning of human tumor cells

We investigated the effects and interactions of epidermal growth factor (EGF), insulin, hydrocortisone, and estradiol on the growth of 18 freshly obtained human tumors in our human tumor stem cell assay (HTSCA) cultured at a reduced serum concentration (8.5% ml). All possible combinations of these four supplement factors were added to the assay to determine the ability of each component to enhance colony formation. We found that hydrocortisone was the most effective single supplement in stimulating colony growth in the HTSCA. Supplementation with insulin, estradiol, or both had some growth-promoting effect but not as great as hydrocortisone. Moreover, the addition of insulin, estradiol, or both often demonstrated a negative interaction with hydrocortisone. EGF supplementation alone; in dual combination with insulin, estradiol, or hydrocortisone; or in combination with estradiol and insulin in the assay did not significantly increase colony formation. However, EGF added to the cultures containing hydrocortisone with insulin and/or estradiol significantly increased colony formation and reversed the negative effect of insulin and estradiol on hydrocortisone activity. Thus, under conditions of our assay, the most effective combination in promoting colony growth contained all four factors.     

The detection of subclasses of granulosa cells with differing responsiveness to EGF, FGF, and gonadotropin preparations using an anchorage-independent clonal agar assay

Subpopulations of granulosa cells of differing responsiveness to epidermal growth factor (EGF), fibroblast growth factor (FGF), pituitary gonadotropin preparations, and rat erythrocyte suspensions (RBC) have been detected using an anchorage-independent clonal agar assay. All growth factor preparations were capable of enhancing colony formation when added alone, and elicited cloning efficiencies as high as 35% when added to the culture system at optimal concentrations in a variety of combinations. The FGF preparation was the single most effective stimulator of colony formation, augmenting both colony numbers and colony size at concentrations as low as 50 ng/ml. However, unlike the other growth factors in this assay system, a plateau in responsiveness could not be reached even at levels as high as 1 microgram/ml. NIH-FSH-P2 and NIAMMD-bLH-4 were considerably less potent than other growth factors. Both preparations were inactive at concentrations less than 1 microgram/ml and produced an optimal response at 10 micrograms/ml.     

Comparison of effects of epidermal and insulin-like growth factors,gastrin releasing peptide and retinoic acid on fetal lung cell growth and maturation in vitro

The role in cell multiplication and maturation of several factors present in the late fetal lung was explored on isolated fetal rat pulmonary fibroblasts and alveolar epithelial type II cells cultivated in serum-free medium. The low degree of reciprocal contamination of each cell population was assessed by immunocytochemistry. Epidermal Growth Factor (EGF) stimulated thymidine incorporation and DNA accumulation in both cell types. In type II cells, it increased labeled-choline incorporation into surfactant phosphatidylcholine (PC), consistently with previous data obtained with lung explant cultures, but not into non-surfactant PC. Insulin-like growth factor (IGF)-I slightly stimulated DNA accumulation in fibroblasts although it did not significantly stimulate thymidine incorporation, contrary to IGF-II which presented a dose-dependent stimulating activity of thymidine incorporation. Neither IGF-I nor IGF-II stimulated type II cell growth. IGFs thus appear to primarily control the growth of lung mesenchyme. In type II cells, they stimulated the most non-surfactant PC biosynthesis. Gastrin releasing peptide (GRP) which was recently reported to promote fetal lung growth in vivo and to stimulate surfactant biosynthesis in lung organ culture revealed as a growth factor for type II cells only, at concentrations below 10 ⁻⁹ M. At concentration 10 ⁻⁸ M, although it did not affect DNA synthesis, GRP tended to increase surfactant and non-surfactant-PC biosynthesis. Retinoic acid inhibited thymidine incorporation into type II cells on a dose-dependent manner but nevertheless enhanced surfactant-PC biosynthesis to a similar extent as EGF. It is suggested that retinoic acid may represent a differentiation or maturation factor for the alveolar epithelium.     

Comparison of effects of epidermal and insulin-like growth factors, gastrin releasing peptide and retinoic acid on fetal lung cell growth and maturation in vitro.

The role in cell multiplication and maturation of several factors present in the late fetal lung was explored on isolated fetal rat pulmonary fibroblasts and alveolar epithelial type II cells cultivated in serum-free medium. The low degree of reciprocal contamination of each cell population was assessed by immunocytochemistry. Epidermal Growth Factor (EGF) stimulated thymidine incorporation and DNA accumulation in both cell types. In type II cells, it increased labeled-choline incorporation into surfactant phosphatidylcholine (PC), consistently with previous data obtained with lung explant cultures, but not into non-surfactant PC. Insulin-like growth factor (IGF)-I slightly stimulated DNA accumulation in fibroblasts although it did not significantly stimulate thymidine incorporation, contrary to IGF-II which presented a dose-dependent stimulating activity of thymidine incorporation. Neither IGF-I nor IGF-II stimulated type II cell growth. IGFs thus appear to primarily control the growth of lung mesenchyme. In type II cells, they stimulated the most non-surfactant PC biosynthesis. Gastrin releasing peptide (GRP) which was recently reported to promote fetal lung growth in vivo and to stimulate surfactant biosynthesis in lung organ culture revealed as a growth factor for type II cells only, at concentrations below 10(-9) M. At concentration 10(-8) M, although it did not affect DNA synthesis, GRP tended to increase surfactant and non-surfactant-PC biosynthesis. Retinoic acid inhibited thymidine incorporation into type II cells on a dose-dependent manner but nevertheless enhanced surfactant-PC biosynthesis to a similar extent as EGF. It is suggested that retinoic acid may represent a differentiation or maturation factor for the alveolar epithelium.     

Growth factors for human tumor clonogenic cells elaborated by macrophages isolated from human malignant effusions

Summary We previously demonstrated that macrophages isolated from human malignant effusions support colony formation of autologous tumor cells in soft agar. We now demonstrate that macrophages (derived from effusions of patients with ovarian, breast, colon, or lung adenocarcinomas) secrete a soluble factor(s) that enhances the ability of a human epithelial tumor cell line (SW-13) to clone in soft agar. Macrophages increased colony growth 5 to 10-fold in a concentration dependent manner, although inhibition of cell growth was observed in the presence of high concentrations of macrophages. We attempted to increase production of tumor colony stimulating factor by exposing macrophages to lipopolysaccharide, concanavalin A, or phytohemagglutinin. Exposure of macrophages to these agents failed to increase their ability to secrete stimulatory factors. Macrophages were cultured for 1 day to 6 weeks in the presence of GCT-CM, a source of granulocyte-macrophage colony stimulating factor and the ability of these cultured macrophages to support colony growth assessed. The ability of macrophages to support colony growth declined gradually with time in culture reaching 50% of control values at 14 days, but remained at this level until 5 weeks of culture. The results of this study indicate the SW-13 cells may provide a quantitative assay for studying monocyte-derived tumor colony stimulating factors.     

Development of human fetal lung in organ culture compared with in utero ontogeny

Summary In utero, at around 23 wk gestation, the progenitor epithelium of distal airway differentiates into type I and type II pneumatocytes. Human fetal lung organ cultures, as early as 12 wk gestation, have the competence to self-differentiate. Distal airway epithelial immunoreactivity to cytokeratins CK 7,8, and 18 decreases with differentiation both in utero and in organ culture, whereas reactivity to epithelial membrane antigen remains constant in both. As distal airways dilate, the mean percentage airspace of fetal lungs in organ culture increases to 58%, equivalent to lung of gestation 26.0±7.3 wk. In organ culture, capillary blood vessels, visualized by vimentin immunoreactivity, remodel and more closely approximate the epithelium but without direct invasion. In utero, at 23 wk gestation, elastin appears as condensation around airways and forms a basis for secondary crests which, by 29 wk gestation, evolve into alveolar septae. In organ culture, no elastin is deposited, no secondary or alveolar crests form, and the lung retains a simple saccular structure. Differentiation of the terminal airway epithelium and mesodermal maturational events to facilitate gas exchange, such as capillary invasion or secondary-alveolar crest formation, are almost synchronous in human lung in utero but clearly dissociate in organ culture.     

Retinoic acid alters EGF receptor expression during palatogenesis

Various growth factors are necessary for normal embryonic development and EGF receptors are present in developing palatal shelves of embryonic/fetal mice at least from day 12 of gestation. The medial epithelium of the palatal shelf undergoes a series of developmental events which do not occur in the oral and nasal epithelia. In utero and in organ culture, the control palatal medial epithelium shows a developmental decline in EGF receptors, demonstrated both by a decrease in the binding of antibody to EGF receptors and a decrease in the binding of 125I-EGF; decreases which are not observed in cells of the adjacent oral or nasal epithelium. During this period, medial cells cease DNA synthesis and undergo programmed cell death. Medial epithelial cells exposed to all-trans-retinoic acid continue to express EGF receptors, bind EGF, proliferate, fail to undergo programmed cell death and exhibit a morphology typical of nasal cells. The data suggest that this disturbance by retinoic acid of EGF receptor localization and subsequent alterations in differentiation of the epithelial cells plays a role in the retinoic-acid-mediated induction of cleft palate.     

Amniotic fluid induces rapid epithelialization in the experimentally ruptured fetal mouse palate--implications for fetal wound healing

Cleft of the secondary palate is one of the most common congenital birth defects in humans. The primary cause of cleft palate formation is a failure of fusion of bilateral palatal shelves, but rupture of the once fused palate has also been suggested to take place in utero. The possibility of post-fusion rupture of the palate in humans has hardly been accepted, mainly because in all the cleft palate cases, the cleft palatal edge is always covered with intact epithelium. To verify whether the intrauterine environment of the fetus plays roles in wound healing when the once fused palate is torn apart, we artificially tore apart fetal mouse palates after fusion and cultivated them in culture medium with or without mouse or human amniotic fluid. We thereby found that the wounded palatal edge became completely covered with flattened epithelium after 36 hours in culture with amniotic fluid, but not in culture without amniotic fluid. Using histological and scanning electron microscopic analyses of the healing process, it was revealed that the epithelium covering the wound was almost exclusively derived from the adjacent nasal epithelium, but not from the oral epithelium. Such actions of amniotic fluid on the fetal wound were never simulated by exogenous epidermal growth factor (EGF), albumin, or both. In addition, the rapid epithelialization induced by amniotic fluid was not prevented by either PD168393 (an inhibitor of the EGF receptor-specific tyrosine kinase) or SB431542 (a specific inhibitor of TGFbeta receptor type I/ALK5). The present study provides new insights into the unique biological actions of amniotic fluid in the repair of injured fetal palate.     

Differential effects of epidermal growth factor and transforming growth factor-beta on synthesis of Mr = 35,000 surfactant-associated protein in fetal lung

Differentiation of pulmonary Type II epithelial cells in late gestation is associated with the synthesis of pulmonary surfactant required for adaptation to air breathing at birth. In the present work, induction of synthesis of a Type II epithelial cell protein, surfactant-associated glycoprotein of Mr = 35,000 (SAP-35) was studied in human fetal lung tissue obtained at 15-24 weeks of gestation. SAP-35 content increased during organ culture in the absence of exogenous hormones. Epidermal growth factor or triiodothyronine stimulated the induction of SAP-35 synthesis during culture. Stimulation by epidermal growth factor (EGF) was detected as early as 2 days and persisted for up to 5 days in culture. Response to EGF was dose-dependent (0.01-10 ng/ml) and was associated with enhanced incorporation of [35S]methionine into immunoprecipitable SAP-35. Increased SAP-35 synthesis was associated with increased SAP-35 RNA as assessed by Northern blot and hybridization assays with human SAP-35 cDNA. Effects of EGF were comparable to the induction of SAP-35 synthesis by 8-bromo-cAMP. In contrast to the stimulatory effect of EGF and triiodothyronine, SAP-35 content was inhibited by transforming growth factor-beta. Both the stimulatory and inhibitory effects of these agents on SAP-35 content were associated with concomitant changes in SAP-35 synthesis. These findings demonstrate multihormonal control of SAP-35 expression and strongly implicate both EGF and transforming growth factor-beta in the regulation of surfactant apoprotein synthesis.     

Effects of epidermal growth factor and transforming growth factor-beta 1 on rat heart endothelial cell anchorage-dependent and -independent growth

This report describes the effects of epidermal growth factor (EGF) and transforming growth factor-beta 1 (TGF-beta 1) on the anchorage-dependent and -independent growth of rat heart endothelial cells (RHE-1A). When RHE-1A cells were grown in monolayer culture with medium containing 10% fetal bovine serum (FBS) supplemented with epidermal growth factor (0.1-100 ng/ml), growth was stimulated fivefold when compared to that of cells grown in medium containing 10% FBS alone. The stimulatory effect of EGF on RHE-1A cell monolayer growth was dose-dependent and half-maximal at 5 ng/ml. The addition of TGF-beta 1 in the range 0.1-10 ng/ml had no effect on RHE-1A cell monolayer growth when added to medium containing 10% FBS alone or 10% FBS supplemented with EGF (50 ng/ml). RHE-1A cells failed to grow under anchorage-independent conditions in 0.3% agar medium containing 10% FBS. In the presence of EGF, however, colony formation increased dramatically. The stimulatory effect of EGF was dose-dependent in the range 0.1-100 ng/ml and was half-maximal at 5 ng/ml. In contrast to its effects under anchorage-dependent conditions, TGF-beta 1 (0.1-10 ng/ml) antagonized the stimulatory effects of EGF on RHE-1A cell anchorage-independent growth. The inhibitory effect of TGF-beta 1 was dose-dependent and half-maximal at 0.1 ng/ml. EGF-induced RHE-1A soft agar colonies were isolated and reinitiated in monolayer culture. They retained the cobblestone morphology and contact-inhibition characteristic of normal vascular endothelial cells. Each of the clones continued to express Factor VIII antigen. These findings suggest that TGF-beta may influence not only endothelial cell proliferation but also anchorage dependence. These effects may in turn be of relevance to endothelial cell growth and angiogenesis in vivo.     

In vitro cytotoxicity assays. Potential alternatives to the Draize ocular allergy test

A short-term cytotoxicity assay carried out in multiwell test plates and a supplementary colony forming assay are both useful for screening and range finding of toxic concentrations of test agents. The highest tolerated dose (HTD), a concentration at which only minimal morphological changes were observed, was designated as endpoint in the assay. Epithelial rabbit cornea cells, murine fibroblasts, Chinese hamster lung cells, human hepatoma cells and mouse macrophage cultures were used as targets. Several of the alcohols tested at HTD in the colony forming assay were found to inhibit colony formation. An ID50 of colony formation was used as a quantitative corroborating test. The ranking of 34 toxicants was found to be virtually the same with all cell types examined. This easily reproducible, rapid in vitro test is cost-effective and can be used for preliminary large scale screening of potential toxicants.Abbreviations HTD highest tolerated dose - EGF epidermal growth factor - FITC fluorescein conjugated anti-guinea pig IgG - DMEM Dulbecco's modified Eagle's medium - FBS fetal bovine serum Supported in part by Revlon, Inc.     

多因素对昆明小鼠胚胎干细胞原代集落形成和后期增殖的影响

目的：研究细胞因子LIF、EGF、bFGF和肝素钠,以及氧分压、温度等多因素对昆明系小鼠胚胎干细胞（KM-ESC）原代集落形成和后期增殖的影响。方法：本研究选择LIF、EGF、bFGF、肝素钠、5%O2,20%O2和37℃、39℃作为研究条件。并检测不同情况下小鼠胚胎干细胞原代集落形成和后期增殖情况。结果：LIF对KM-ESC原代集落形成和后期增殖具有显著促进作用,极显著高于EGF、bFGF和肝素钠组（P〈0.01）。温度对KM-ESC原代集落形成和增殖具有显著影响,39℃条件下,原代集落形成率、直径和后期增殖显著高于37℃（P〈0.05）;而氧分压对KM-ESC原代集落形成无显著作用（P〉0.05）,但是对原代集落直径和后期增殖有一定促进作用,20%O2组显著高于5%O2组（P〈0.05）。结论：LIF、EGF、bFGF、肝素钠、39℃、20%O2对小鼠胚胎干细胞原代集落形成和后期增殖具有显著促进作用。     

EFFECTS OF ADENOSINE AND EPIDERMAL GROWTH FACTOR ON THE GROWTH OF MOUSE MAMMARY EPITHELIAL CELLS

The objective of this study was to determine if adenosine alters growth of mammary epithelium. Mouse mammary epithelial cells (NMuMG) were cultured in DMEM supplemented with 10% fetal calf serum. After serum starvation for 24h, EGF (0–100ng/ml) and/or adenosine (0–100μm ) was added. Adenosine at concentrations of 1, 10 or 100μm increased DNA synthesis significantly, when compared to control. Addition of epidermal growth factor (EGF) (10ng/ml) into 1 or 10μm adenosine showed the interaction in DNA synthesis between EGF and adenosine. A similar result was observed when 100μm adenosine added to various concentrations of EGF (0–100ng/ml). In the second mammary gland (thoracic) organ culture studies, mammary development scores were increased by adenosine (100μm ), EGF (100ng/ml) and adenosine plus EGF. These results indicate that the purine nucleoside adenosine stimulates mammary epithelial cell growth and interacts with EGF in DNA synthesis of mouse mammary epithelial cells.     

Presence and characteristics of epidermal growth factor receptors in human fetal small intestine and colon

In the present study, we demonstrate for the first time the presence of important concentrations of EGF binding sites in isolated epithelial cells of both human fetal small intestine and colon as early as 12 weeks gestation. The pattern of EGF binding in the small intestine between 12 and 17 weeks show that binding was significantly higher (2.5-fold) in younger fetuses than in older fetuses. Moreover, the fetal colon exhibited a much higher binding capacity (1.5-2.5 times) than corresponding intestinal cells for all age groups studied. Analysis of Scatchard representations reveal that the concentration of high- and low-affinity binding sites in colonic epithelial cells are twice the values observed in corresponding intestinal cells. The present data raise interesting possibilities as to the role of this growth factor in human fetal gut development.