The vasoactive intestinal peptide (VIP) receptor: recent data and hypothesis

Vasoactive intestinal peptide (VIP) is a neuropeptide with a broad range of biological activities in various tissues. After interaction with its membrane receptor, VIP generally induces a very large increase in the intracellular cyclic AMP level. Receptors for VIP have been described in numerous tissues and cell lines. The first results on VIP receptor structure have been obtained by covalent cross-linking using bifunctional reagents. The molecular mass of the different components characterized in this way differs greatly according to the species and the tissue used. This heterogeneity may reflect either a difference in the length of the cross-linked polypeptide backbone or differently glycosylated forms of the same polypeptide. The VIP binding site of intact human adenocarcinoma cells (HT29 cells) is an Mr 64,000 glycoprotein with 20kDa of N-linked oligosaccharide side chains containing sialic acid. The structure of the VIP binding site from HT29 cell is compared, first to the structure of the VIP receptor from other tissues, particularly that from rat liver, and second to the structure of the hepatic glucagon binding site. Recently, solubilization of the VIP receptor in an active form has provided a new way of studying this receptor. The HT29 cell line is an appropriate model to study the dynamics of the VIP receptor. After binding to its receptor, VIP is rapidly internalized, probably by receptor-mediated endocytosis. This internalization leads to a decrease in the cell surface receptor number and simultaneously to a homologous desensitization of adenylate cyclase. VIP is then degraded in the lysosomes, while most of the receptors are recycled back to the cell surface. The presence of an intracellular pool of unoccupied VIP receptors has been demonstrated after inactivation of the cell surface receptors by chymotrypsin. The kinetics of the receptor reappearance at the cell surface, after inactivation by chymotrypsin or after receptor-mediated endocytosis, indicate 2 possible intracellular pathways for occupied and unoccupied VIP receptors.

Analysis of selected elements in tobacco by wavelength dispersive X-ray fluorescence spectrometry

A rapid method for the determination of 16 elements in tobacco by wavelength dispersive X-ray fluorescence spectrometry has been developed. The method is accurate and precise, and requires only 9 min per sample for quantitation. Sample preparation consists of placing a portion of dried, ground tobacco in a sample cup, and pressing at 25 tons pressure to make a compressed pellet. This pellet is then automatically analyzed by X-ray fluorescence for 16 elements. The results are stored on a computer disk for future recall and report generation.

Restricted localization of functional vasoactive intestinal peptide (VIP) receptors in in vitro differentiated human colonic adenocarcinoma cells (HT29-D4)

HT29-D4, a clone of the human colonic adenocarcinoma cell line (HT29), possesses at its cell surface specific binding sites for the vasoactive intestinal peptide (VIP) (KD = 0.5 nM). Their molecular weight was previously estimated to 117 kDa and 64 kDa. This clone underwent functional and structural differentiation when grown in a glucose-free galactose-containing medium. The [125I]VIP binding capacity of cells grown in this medium gradually declined while the cell density increased and reached a value close to zero when cell monolayer was able to form hemicysts. At this time, cells presented numerous tight junctions and desmosomes and a well organized brush border. Binding capacity could be recovered when the post-confluent monolayers were previously disaggregated with EDTA. Neither the affinity for VIP nor the molecular weight of the [125I]VIP cross-linked polypeptides were modified in these cells compared to cells grown in glucose-containing medium. However, surface receptor number of differentiated cells was twice that of undifferentiated cells. Leakproof differentiated cell monolayers grown on permeable substratum produced cAMP in response to VIP only when the peptide was present in the lower chamber of the culture wells. Taking these data altogether, we conclude that the localization of functional VIP receptors is restricted to the basolateral domain in differentiated post-confluent HT29-D4 cells.

Appearance of prostaglandins, thromboxane B2, and hepoxilin A3 in the circulation of the normal and diabetic (BB) rat after arachidonic acid administration--correlation with plasma insulin

The temporal in vivo expression of the eicosanoids (products of the cyclooxygenase pathway and one product of the 12-lipoxygenase pathway, hepoxilin A3) was investigated after bolus intravenous injection of arachidonic acid in the normal rat and in the genetic rat model of type I insulin-dependent diabetes, the diabetic BB rat. The temporal relationship between the expression of these products and plasma insulin concentrations was also investigated to determine whether any correlation existed between the rise in plasma insulin levels and any of the newly formed eicosanoids. Measurements of the eicosanoids present in whole blood were carried out using the deuterium isotope dilution technique involving separation of pentafluorobenzyl esters, O-methyl oximes, and trimethylsilyl ether derivatives by high-resolution gas chromatography and specific detection by negative ion chemical ionisation mass spectrometry in the selected ion mode. Injection of arachidonic acid resulted in large and statistically significant increases in the blood concentrations of all products within 1 min, with thromboxane B2 (the stable product of thromboxane A2) and trioxilin A3 (the stable product of hepoxilin A3) being the highest (4.5-12 ng/mL). The mean concentrations of thromboxane B2 and trioxilin A3 in blood appeared greater in the diabetic BB rat than in the normal rat, while the opposite was found for 6-keto PGF1 alpha (the stable product of prostacyclin). The apparent greater ratio of thromboxane B2 to 6-keto PGF1 alpha in the diabetic BB rat than in the normal rat supports a prothrombotic nature of platelets associated with diabetes.

Modification of neuronal muscarinic receptor-mediated responses by islet-activating protein

Islet-activating protein (IAP) was used to investigate the role of the guanosine triphosphate binding proteins Gi and/or Go in muscarinic acetylcholine receptor-mediated responses in neuroblastoma cells (clone N1E-115). Incubation of intact cells for 24 h with 20 ng/ml IAP resulted in inhibition of subsequent IAP catalyzed incorporation of [32P]ADP-ribose into a membrane protein doublet of molecular weight 40,000 (Gi alpha and Go alpha). IAP treatment fully blocked muscarinic receptor-mediated inhibition of cAMP accumulation. Incubation of intact cells with carbachol for 8 h resulted in the concentration dependent loss of membrane muscarinic receptor. Pretreatment of cells with IAP prior to carbachol exposure partially blocked the subsequent decrease in receptor number. Pretreatment of cells with IAP had no effect on the ability of carbachol to stimulate phosphoinositide hydrolysis in neuroblastoma cells. Thus, while the guanosine triphosphate binding proteins Gi and/or Go are involved in coupling the muscarinic receptor to some of the physiological responses in these cells, it is clear that activation of phospholipase C by the muscarinic receptor is a Gi/Go independent response.

Intensity images and statistics from numerical simulation of wave propagation in 3-D random media

An extended random medium is modeled by a set of 2-D thin Gaussian phase-changing screens with phase power spectral densities appropriate to the natural medium being modeled. Details of the algorithm and limitations on its application to experimental conditions are discussed, concentrating on power-law spectra describing refractive-index fluctuations of the neutral atmosphere. Inner and outer scale effects on intensity scintillation spectra and intensity variance are also included. Images of single realizations of the intensity field at the observing plane are presented, showing that under weak scattering the small-scale Fresnel length structure of the medium dominates the intensity scattering pattern. As the strength of scattering increases, caustics and interference fringes around focal regions begin to form. Finally, in still stronger scatter, the clustering of bright regions begins to reflect the large-scale structure of the medium. For plane waves incident on the medium, physically reasonable inner scales do not produce the large values of intensity variance observed in the focusing region during laser propagation experiments over kilometer paths in the atmosphere. Values as large as experimental observations have been produced in the simulations, but they require inner scales of the order of 10 cm. Inclusion of an outer scale depresses the low-frequency end of the intensity spectrum and reduces the maximum of the intensity variance. Increasing the steepness of the power law also slightly increases the maximum value of intensity variance.

HT 29, a model cell line: stimulation by the vasoactive intestinal peptide (VIP); VIP receptor structure and metabolism

HT 29, a cell line derived from a human colonic adenocarcinoma, is highly responsive to the vasoactive intestinal peptide (VIP) as shown by a more than 100-fold intracellular cAMP increase (Ka = 0.3 nM), the stimulations of protein kinase A (Ka = 0.1 nM) and the low-Km cAMP phosphodiesterase (Ka = 40 nM). Remarkably, adenylate cyclase, cAMP-dependent kinase and cAMP-specific phosphodiesterase are activated in a sequential manner. Binding studies with [125I]-labeled VIP indicate a high affinity site with a Kd value (0.5 nM) close to the activation constant value (Ka) of the three enzymes. The molecular structure of the VIP receptor was studied by immunological and chemical approaches. A monoclonal antibody (mAb 109-10-16) which partially decreased the binding of VIP to its receptor allowed the characterization of Mr = 53,000 and Mr = 48-49,000 polypeptides. More precise identification of protein components of the VIP receptor resulted from covalent cross-linking on intact HT 29 cells by four bifunctional reagents: dithiobis-(succinimidyl propionate) and its non-cleavable analog disuccinimidyl suberate, the photoactivable azido phenyl glyoxal and dimethylpimelimidate. Analysis by SDS-polyacrylamide gel electrophoresis demonstrated a major band of Mr = 67,000 regardless of which cross-linker was used. The same band and an Mr = 49,000 species were found in experiments using a crude membrane fraction of HT 29 cells. Assuming one molecule of VIP (Mr = 3326) linked per polypeptide, these observations suggest that an Mr = 64,000 species belongs to the VIP specific plasma membrane receptor. This protein contains an Mr = 20,000 N-linked sialic acid rich oligosaccharidic moiety.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a critical role of diet in the development of insulin-dependent diabetes mellitus

The role of diet in human insulin-dependent diabetes mellitus (IDDM) has not been properly examined, mainly due to a lack of reliable markers to identify prospective diabetics and the difficulties in obtaining accurate and representative dietary information. Nonetheless, there is some circumstantial evidence suggesting a role for diet in human IDDM. The validity of this relationship in humans must await a sufficiently large, well designed prospective study or the discovery of better markers for diabetes predisposition. The recent availability of the spontaneously diabetic BB rat has permitted prospective studies under controlled conditions which indicate diet, particularly dietary proteins, such as wheat gluten or cow's milk proteins may be prerequisites for maximum expression of the insulin-dependent syndrome in these animals. The early suckling and/or post-weaning period appears to be important and may be the crucial time when these proteins or portions of them pass the gastrointestinal barrier and initiate a process, possibly immunological, which results in destruction of the beta cells of the pancreas.

Photoaffinity labelling of the vasoactive-intestinal-peptide-binding site on intact human colonic adenocarcinoma cell line HT29-D4. Synthesis and use of photosensitive vasoactive-intestinal-peptide derivatives

N-Hydroxysuccinimidyl 4-azidobenzoate, a u.v.-sensitive heterobifunctional reagent, was used to synthesize photoreactive derivatives of the vasoactive intestinal peptide (VIP). Products of the reaction were purified by reverse-phase h.p.l.c. Three 4-azidobenzoyl-VIP (4-AB-VIP) derivatives were able to compete with monoiodinated 125I-VIP with an apparent KD of 2.5, 6.3 and 12.5 nM compared with 0.6 nM for native VIP. H.p.l.c.-purified mono[125I]iodinated VIP was used to synthesize 4-AB-125I-VIP derivatives. They were used to photoaffinity-label the VIP-binding site of HT29-D4 cells, a clone derived from the human colonic adenocarcinoma cell line HT29. Only one polypeptide, of Mr 70,000 +/- 5000 (mean +/- S.D.) was specifically labelled. The Mr of the component thus characterized was slightly higher than that of the major species (Mr 67,000) labelled after cross-linking experiments using 125I-VIP, conventional homobifunctional reagents and HT29 cells. Nevertheless, the specificity and extent of glycosylation of these two components were identical. These new photosensitive VIP derivatives should be useful tools with which to investigate further VIP-receptor structure and metabolism.

Multicore myopathy: not always a benign entity

Four patients with Multicore Myopathy, a rare morphologically distinct myopathy, are described. Although previously considered to be a non-progressive or only slowly progressive myopathy, progression to significant disability was seen in three of our cases. The association of cardiac disease with Multicore Myopathy has not been previously emphasised. All four patients in this study had a cardiomyopathy, and heart disease was the cause of death in two of the patients. Multicore Myopathy is not always a benign entity. Cardiac involvement, when present, adversely affects prognosis.

Time-dependent change in electrophysiologic milieu after myocardial infarction in conscious dogs

This study was designed to assess the time-dependent change in propensity to induction of malignant ventricular tachyarrhythmia after myocardial infarction. Instrumented conscious dogs were assessed during serial drug-free electrophysiologic studies over 26 +/- 9 days (range 17 to 35 days) after 2 hr occlusion-reperfusion of the left anterior descending coronary artery. Of the 19 animals studied, 11 continued to have sustained ventricular tachyarrhythmias inducible (group I) over this time period. In the eight remaining animals, spontaneous loss in the ability to induce sustained ventricular tachycardia occurred (group II). Myocardial infarct size in group I animals (18 +/- 8%) was significantly greater than that in group II dogs (12.5 +/- 5%; p less than .05). Even in group I animals, time-dependent changes occurred in the number of extrastimuli required to induce ventricular tachycardia and the frequency with which left ventricular stimulation was necessary. A differential pattern of time-dependent changes in electrophysiologic variables was observed when comparing group I and II animals. The conduction time to the infarct zone was prolonged during follow-up in group I animals, while in group II animals this variable was unchanged. Repolarization time recorded in the border zone remained unchanged in group I animals, but it was significantly shortened in group II animals. In addition, ventricular effective refractory period in the infarct zone shortened over time in group I animals but did not change in group II animals. In conclusion, time-dependent changes occur in electrophysiologic variables that are associated with a progressive decrease in propensity to induction of ventricular tachycardia after myocardial infarction. A critical determinant of whether propensity to ventricular tachycardia resolves over time is size of myocardial infarction.

The effects of interferon on glial cells

The effects of a partially purified rat interferon (RIF) on cell lines cloned from a chemically induced rat glioma (A15A5) and normal rat brain (ARBOC9) were investigated. Interferon treatment reduced the rate of exponential growth and saturation density of both cell lines, but induced contrasting morphological changes. A15A5 cells became bipolar, developed longer processes and produced less extracellular fibronectin, whereas ARBOC9 cells became enlarged, showed increased multinuclearity, expressed more fibronectin and contained actin-like cytoplasmic filaments. These findings demonstrate that RIF has an antiproliferative activity in vitro on both neoplastic and non-neoplastic astrocytes, but that morphological and immunocytochemical responses differ.

In vivo formation of hepoxilin A3 in the rat

Bolus intravenous injection of arachidonic acid (10 mg/kg) in the rat led to the appearance of hepoxilin A3 in the circulation. The product was assayed as the Me t-BDMSi derivative of its stable trihydroxy product trioxilin A3, by capillary gas chromatography-electron impact mass spectrometry using the stable deuterium isotope dilution technique. Hepoxilin A3, was undetected in blood samples taken prior to the injection of arachidonic acid, but rapidly appeared (4.62 +/- 1.3 ng/ml blood, n = 3) within 1 minute after injection of arachidonic acid. The plasma concentration of insulin increased by 36% over the same period after injection of arachidonic acid. These experiments demonstrate for the first time the formation of this new class of insulin secretagogues in vivo and their temporal correlation with plasma insulin concentrations in vivo.

Differential immunohistochemical reactions of carcinoid tumors

Neuron-specific enolase, S-100 protein, and Leu 7 are present in cells showing neuroendocrine differentiation. Leu 7 recognizes myelin-associated glycoprotein, and recent evidence suggests that it further recognizes a subset of neurosecretory granules. Forty-six primary and metastatic carcinoid tumors from various sites were evaluated immunohistochemically with antisera to neuron-specific enolase, S-100, and Leu 7. Only one tumor, a rectal carcinoid, failed to stain with neuron-specific enolase. The remaining cases showed four patterns of staining: nuclear, diffuse cytoplasmic, globular cytoplasmic, or mixed. The pattern of reaction did not correlate with either the embryonic origin or histologic pattern of the tumor. Two patterns of staining were obtained with anti-Leu 7: diffuse cytoplasmic, or dot or ring-like deposition of reaction product. The latter pattern was entirely confined to appendiceal carcinoids. Reactivity with S-100 was in the form of dense positivity in individual cells having a stellate outline. Less intense cytoplasmic positivity and, uncommonly, a mixture of both types of staining were also seen. These histochemical results may lend support to recent evidence suggesting the existence of identifiable subsets of neurosecretory granules in neuroendocrine tumors, including carcinoids.

Cycloheximide induces accumulation of vasoactive intestinal peptide (VIP) binding sites at the cell surface of a human colonic adenocarcinoma cell line (HT29-D4). Evidence for the presence of an intracellular pool of VIP receptors

Incubation of monolayers of HT29-D4 cells (a clone of the human colonic adenocarcinoma cell line HT29) in the presence of 17.5 microM cycloheximide resulted in an increase in the number of vasoactive intestinal peptide (VIP) binding sites at the cell surface without any change in the affinity of receptor for its ligand. The increase in 125I-VIP-binding capacity was dose-dependent between 0.35 microM and 17.5 microM cycloheximide and was correlated with the inhibition of protein biosynthesis. At higher concentrations of drug (17.5-100 microM) a plateau corresponding to a twofold increase in VIP-binding capacity was reached independently of the extent of protein synthesis inhibition. We found that VIP receptors of HT29-D4 cells with such an enhanced binding capacity behaved like those of control cells with respect to receptor internalization and recycling (i.e. the cycle of occupied receptors was insensitive to cycloheximide). After inactivation of 90% of cell-surface VIP receptors by alpha-chymotrypsin, we observed a biphasic kinetic of reappearance of VIP-binding sites. 40% of VIP-binding sites reappeared very quickly (less than 5 min) and 100% within 17 h. The fast recovery of VIP receptors was probably due to the deployment of new binding sites from an intracellular pool. The rate and extent of recovery of these receptors were similar in control cells and in cycloheximide-treated cells. However, the slow recovery was inhibited in cycloheximide-treated cells probably because a pool of immature receptors was depleted by the drug before the alpha-chymotrypsin treatment. Our data are consistent with the existence of two different intracellular pathways of occupied and unoccupied VIP receptors.

Dietary triggers of insulin-dependent diabetes in the BB rat

Environmental "triggers" (including viruses, toxins and dietary factors) have been implicated in the pathogenesis of insulin-dependent diabetes mellitus. Data have suggested a possible role for cow's milk protein (CMP) as a trigger of diabetes. To study this further, 86 BB rats were divided into 2 groups during the weaning period (days 13-25): Group A received rat chow without CMP; Group B, rat chow with 1% CMP added. Each group was subdivided afterwards into 2: Groups A1 and B1 received chow without CMP; Groups A2 and B2, chow with CMP. Animals weaned with chow containing CMP (B1 and B2) had a higher incidence of diabetes (66%) than those weaned without (A1 and A2; 29%, p less than 0.001). The incidence in both B1 and B2 was significantly greater than in either A1 or A2 (p less than 0.05). The highest incidence of diabetes occurred in male rats weaned on rat chow with CMP (90%), the incidence being significantly higher than female rats weaned with (43%) or without CMP (18%) and males weaned without CMP (39%). Thus, it appears that (a) the presence of cow's milk protein in the diet increases the incidence of diabetes in the BB rat; (b) the critical time for exposure to CMP appears to be the weaning period; and (c) male rats appear to be more susceptible to the development of diabetes than female rats, when exposed to this trigger. This supports the hypothesis that dietary triggers may play an important role in the expression of diabetes in the susceptible host and that its prevalent action occurs early in life.

The vasoactive intestinal peptide receptor on intact human colonic adenocarcinoma cells (HT29-D4). Evidence for its glycoprotein nature

We have previously shown that the mono [125I]iodinated vasoactive intestinal peptide (125I-VIP) could be covalently cross-linked on intact colonic adenocarcinoma cells (HT29). A major Mr 67,000 and a minor Mr 120,000 cross-linked polypeptides have been characterized [Muller, Luis, Fantini, Abadie, Giannellini, Marvaldi & Pichon (1985) Eur. J. Biochem. 151, 411-417]. The glycoprotein nature of these species was investigated using endo-beta-acetylglucosaminidase F (Endo F) treatment, enzymic and chemical desialylation and wheat germ agglutinin (WGA)-Sepharose affinity chromatography. Affinity-labelled VIP-binding proteins solubilized by Nonidet P-40 bound to WGA-Sepharose and could be eluted specifically with N-acetyl-D-glucosamine. Treatment with Endo F resulted in an increased electrophoretic mobility of both polypeptides. The major and the minor VIP-binding proteins were converted respectively into Mr 47,000 and 100,000 species, indicating removal of 20 kDa of N-linked oligosaccharides. Deglycosylation with trifluoromethanesulphonic acid also led to a 20 kDa loss in mass of the Mr 67,000 component, indicating the absence of additional O-linked sugars on this polypeptide. The presence of sialic acid on the major VIP-binding protein was demonstrated after treatment of intact cells with neuraminidase or by chemical desialylation with hydrochloric acid. We conclude from this study that the VIP receptor from intact HT29-D4 cells is a glycoprotein with N-linked oligosaccharide side chains containing sialic acid.

Functional and physical properties of chick atrial and ventricular GTP-binding proteins: relationship to muscarinic acetylcholine receptor-mediated responses

Activation of muscarinic acetylcholine receptors in chick atria, but not ventricles, causes an increase in K+ permeability. Because of suggestions that this difference in muscarinic receptor-mediated physiological responses may be due to changes in the guanine nucleotide regulatory proteins (termed Go and Gi) associated with the receptor, we compared the functional and biochemical properties of these proteins in atria and ventricles from 8-day chick embryos. The affinity of agonist for the muscarinic receptor in either the absence or presence of guanine nucleotides was the same in membranes from atria and ventricles; similar concentrations of guanyl-5'-yl imidodiphosphate were required to regulate agonist binding in both tissues (EC50 of 2.7 X 10(-8) and 2.0 X 10(-8) M for atria and ventricles, respectively). Forskolin-stimulated adenylate cyclase activity in atria and ventricles was equally sensitive to inhibition by guanyl-5'-yl imidodiphosphate. In addition, the muscarinic agonist carbachol inhibited adenylate cyclase in ventricles with an IC50 similar to that observed in atria, although the magnitude of inhibition was slightly less in ventricles. The physical properties of the alpha subunits of the guanine nucleotide regulatory proteins were examined after covalent modification by islet activating protein. Two [32P]ADP-ribosylated polypeptides were detected by one dimensional gel electrophoresis, with molecular weights equal to those reported for Go and Gi from other tissues. Similar amounts of both proteins were found in atrial and ventricular membranes. Peptide mapping demonstrated that although the 39 and 42 kD proteins had nonidentical peptide maps, atrial and ventricular peptide maps were identical.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell death in the embryonic brain of Gallotia galloti (Reptilia; Lacertidae): a structural and ultrastructural study

In the striatum, thalamus and cerebellum of a Lacertid reptile, we have found three types of cellular death during embryonic development, both at the light and electron microscopic level. The first affects the undifferentiated neuro-epithelial cells and is commonest during the early stages (E. 32-E. 36). The second corresponds to the type of 'nuclear' death described in the bibliography and reaches a maximum in the middle embryonic period (E. 37-E. 39); nevertheless important variations were observed in different zones. The third is the same as the 'cytoplasmic' death type and appears in the perinatal stages. Phagocytosis involved in the elimination of dead cells is of two types. One is associated with early death and is carried out by undifferentiated neuro-epithelial cells. The other is carried out by microglial cells which appear around Stage 37. Much cellular debris was observed in the intermediate zone and this was associated with the second type of phagocytosis. In both cases lipid production was associated with the degenerative process. Comparison of the temporal cellular death pattern with synaptogenesis, gliogenesis and maturation of neuronal processes is consistent with the view that the various types of cellular death found by us had different causes.

Serum insulin-releasing activity and the Prader-Willi syndrome

Pathogenesis and etiology of the various clinical features of the Prader-Willi syndrome (PWS) are not completely understood. There is evidence suggesting a hypothalamic abnormality leading to hypogonadism in this syndrome. To test the possible hypothalamic involvement in the pathogenesis of obesity in these patients we studied the sera of 5 patients with PWS for insulin-releasing activity of possible hypothalamic origin. In addition 4 patients with a PWS-like syndrome and 6 obese patients with signs of central nervous system damage were studied. All five patients with PWS showed significant insulin-releasing activity in their sera. Of the four patients with PWS-like symptoms three showed similar activity while three of the obese patients with central nervous system damage had this activity in their sera. Serum insulin-releasing activity has been shown earlier to be associated with childhood obesity and it could play a role in the pathogenesis of obesity in PWS.

Heterogeneity of a cultured neoplastic glial line. Establishment and characterisation of six clones

Six clones have been established from a tumorigenic glial cell line (VMDk P497) originally derived from a spontaneous mouse astrocytoma. The clones express dissimilar morphological, antigenic, kinetic and chromosomal properties, thereby indicating the heterogeneity of the parent culture line.

Insulinotropic activity in the serum of obese and nonobese infants and children

The ability of a serum fraction, mol wt 1000-5000, to stimulate insulin release in vitro was studied in 123 obese and normal weight children aged 0-17 yr. The sera were fractionated by serial molecular filtration after treatment with urea. Stimulation of insulin release was determined with a bioassay using isolated rat islets in perifusion. The islet-stimulating activity was found in all obese children less than the age of 10 yr and in the majority of the obese children older than 10 yr of age. In normal weight children the activity was also found in the majority of infants, but was infrequent in older children. The serum islet-stimulating activity was positively correlated with the duration and degree of obesity and with linear growth rate. The molecular structure and origin of the insulinogenic activity in the serum is still unknown. In high-performance liquid chromatography it has the same elution characteristics as the hypothalamic insulin-glucagon liberin. The present results suggest a role for the serum islet-stimulating activity in the pathogenesis of obesity.

Distribution of the Mr 52,000 estrogen-regulated protein in benign breast diseases and other tissues by immunohistochemistry

A secreted glycoprotein with a molecular weight of 52,000 is induced by estrogen in breast cancer cells and has been purified to prepare monoclonal antibodies. The protein has been detected in some breast cancers but not in normal breast and uterus. In order to study its potential value as a marker, we have tested by immunohistochemistry frozen sections of several normal and malignant tissues and of benign mastopathies. Among different tissues tested, the Mr 52,000 protein was detected only in liver, sweat glands, and some sebaceous glands, and in malignant melanomas and some breast tumors. Other estrogen-responsive tissues (ovary, placenta, endometrium, etc.) gave negative results. Immunoradiometric assay of the Mr 52,000 protein in biological fluid revealed an elevated concentration in cyst fluid (0.5 to 7.4 micrograms/ml), pleural effusions of certain metastatic breast cancer, and sweat. By immunohistochemistry, the Mr 52,000 antigen was also detected in 42% of 129 benign mastopathies. Gynecomastia, fibrous disease, fibroadenoma, and adenosis were mainly negative, whereas ductal hyperplasia and cysts were positive. The Mr 52,000 protein was found mostly in proliferative ducts and in cysts but not in lobular hyperplasia and nonproliferative lesions without cyst. More Mr 52,000 protein was found in postmenopausal patients than in premenopausal patients. We conclude that the Mr 52,000 protein is a marker associated with mammary cysts and proliferative ducts. On the basis of the increased risk of breast cancer in proliferative mastopathies, we suggest that the Mr 52,000 protein is useful for predicting high-risk mastopathies acting as a marker associated with the proliferation of ductal tissue.