Biomedical subjects

A Varro

Publications and source records attributed to A Varro.

At least 55 records · Page 3Linked to original sources

PubMed1996

Gastrin gene expression is required for the proliferation and tumorigenicity of human colon cancer cells.

The majority of human colon cancers express the gastrin gene, and a significant percentage bind gastrin-like peptides. However, it is not known if gastrin gene products are physiologically relevant to the growth and proliferation of human colon cancers. To investigate the functional role of gastrin gene expression, we examined the effect of gastrin antisense (AS) RNA expression on the growth and tumorigenicity of colon cancer cells. The full-length human gastrin cDNA was cloned in the AS direction in a retroviral vector under the transcriptional control of human cytomegalovirus promoter. Three representative human colon cancer cell lines that expressed negligible (Colo-205A) to significant (Colo-320 and HCT-116) levels of gastrin mRNA were transfected with either AS or control vectors and subjected to various growth studies in vitro and in vivo. The proliferative and tumorigenic potential of the AS clones from the gastrin-expressing cell lines was significantly suppressed compared to that of the control clones, whereas the growth of Colo-205A-AS cells (the negative control) was similar to that of the Colo-205A-C-cells, indicating the relative specificity of the antitumorigenic effects of AS gastrin RNA expression. We believe that this is the first evidence that supports a possible critical role of gastrin gene expression in the tumorigenicity of human colon cancers that express the gastrin gene. Because > 60-80% of human colon cancers express the gastrin gene, it can be expected that the growth of a significant percentage of these cancers may be critically dependent on the expression of gastrin gene products. Therapeutic measures, such as the AS strategy used in the present study, may therefore prove to be useful in treating human colon cancers in the future.

Animals↗

PubMed1996

Discrimination between constitutive secretion and basal secretion from the regulated secretory pathway in GH3 cells.

The present experiments were undertaken to characterize basal release from vesicles of the regulated secretory pathway. In transfected GH3 cells, progastrin was released by the constitutive route, and mature, bioactive, amidated gastrin by the regulated secretory pathway. Studies using brefeldin A and bafilomycin A1 which inhibit progression through the Golgi complex suggested that both basal and stimulated release of amidated gastrin originated from mature secretory granules. Basal, but not stimulated, secretion of amidated gastrin was strongly inhibited at 22 degrees C. Mature secretory vesicles therefore support both basal and evoked secretion although the mechanisms underlying the two processes differ in their temperature sensitivity.

Amides↗

PubMed1996

Gastrimmune raises antibodies that neutralize amidated and glycine-extended gastrin-17 and inhibit the growth of colon cancer.

The effect of gastrin neutralization was evaluated on the in vivo growth of the rat colon line, DHDK12, which expressed cholecystokinin B/gastrin receptors and secreted glycine-extended gastrin-17 (G17). Gastrin neutralization was achieved by administration of the immunogen, Gastrimmune, which is composed of the amino terminal portion of G17 linked to a diphtheria toxoid. A rat-specific version of Gastrimmune was used to preimmunize rats, with control animals receiving diphtheria toxoid only. The antibodies raised neutralized both carboxy-amidated and glycine-extended G17. The tumor was implanted into the muscle layer of the abdominal wall, and rats immunized with Gastrimmune had significantly reduced median cross-sectional tumor areas (70.2% reduction; P = 0.005) and weights (56.5% reduction; P = 0.0078)) when compared to control rats. Histological analysis revealed that the tumors had an enhanced degree of necrosis, with the area of viable tumor in the Gastrimmune-immunized rat reduced to 40.3% compared to 58.6% in the control rats (P = 0.003). Immunization with Gastrimmune raised antibodies that inhibited the growth of a rat colon tumor. This could have been mediated by neutralization of both serum G17 and cell-associated precursor gastrin molecules.

Amino Acid Sequence↗

PubMed1996

Electrical restitution in rat ventricular muscle.

The mechanism of electrical restitution was studied in isolated rat ventricular muscle using drugs that inhibit specific ion currents. The effect of transient changes in cytosolic Ca concentration and Na/Ca exchange in relation to the restitution process was also studied in single ventricular cardiomyocytes. Conventional microelectrode techniques were applied to record action potentials having gradually increasing coupling intervals, each evoked following a train of stimuli with a frequency of 1 Hz. Ion currents were recorded from enzymatically isolated cells using the whole cell patch clamp technique. Ca transients were monitored in myocytes loaded with the fluorescent dye, indo-1. The electrical restitution process in multicellular rat ventricular preparations at 37 degrees C was described as a sum of three exponential components: an early positive component, a subsequent fast negative component and a late negative component, having time constants of 21.9 +/- 1.9, 73.1 +/- 6.0 and 1053 +/- 61 ms, respectively (n = 9). Inhibition of the transient outward K current, the delayed rectifier K current, or the chloride current did not substantially alter these time constants. The early positive and fast negative components were fully abolished by nifedipine or MnCl2. In the presence of caffeine, the fast negative component was absent, while the time constant of the early positive component increased to 39.5 +/- 5.8 ms (n = 5). In single myocytes loaded with indo-1, the Ca transients decayed with a time constant of 151 +/- 12 ms at room temperature (n = 5). These Ca transients were accompanied by inward current tails, identified as a Na/Ca exchange current, having a decay time constant of 140 +/- 4.5 ms. It is concluded that electrical restitution in rat ventricular muscle is relatively little affected by recovery from voltage-dependent inactivation of ion channels, it is rather governed by transient changes in cytosolic Ca concentration possible via Ca-dependent inactivation of the L-type Ca current and activation of the Na/Ca exchange current.

Action Potentials↗

PubMed1996

Control of preprogastrin messenger RNA translation by gastric acid in the rat.

BACKGROUND & AIMS: Plasma gastrin and tissue preprogastrin messenger RNA (mRNA) increase in rats treated with the proton pump inhibitor omeprazole, but changes in mRNA alone cannot account for calculated changes in gastrin synthesis. The possibility that there is control of preprogastrin mRNA translation rates was investigated. METHODS: Preprogastrin mRNA translation was assessed by incorporation of [3H]tyrosine into progastrin in rat antral mucosa in vitro at 22 degrees C; preprogastrin mRNA was determined by Northern blot analysis. RESULTS: During incubation, incorporation of [3H]tyrosine into progastrin was linear up to 4 hours, and preprogastrin mRNA was unchanged. Fasting (24 hours) decreased plasma gastrin levels by 75% and progastrin translation by 40%, but preprogastrin mRNA was unchanged. Conversely, omeprazole increased plasma gastrin levels 8-fold, preprogastrin mRNA 2-3-fold, and progastrin translation 6-fold. In a cell-free translation system, preprogastrin was increased in samples from omeprazole-treated rats in direct proportion to the increase in preprogastrin mRNA abundance. CONCLUSIONS: Stimulation of gastrin cells by achlorhydria or inhibition by fasting lead, respectively, to increased and decreased preprogastrin translation rates that are more pronounced than changes in mRNA abundance. Therefore, luminal acid controls preprogastrin mRNA translation independently of changes in mRNA abundance or gastrin release.

Animals↗

PubMed1996

Physiological regulation of gaba uptake by rat pyloric antral mucosa.

Endocrine cells of the pyloric antral mucosa are known to take up gamma-amino-n-butyric acid (GABA), but the functional significance of this is uncertain. We now report that specific uptake of [3H]GABA by rat antral, but not corpus, mucosa is enhanced after fasting for 48 h. Decreased extracellular GABA in fasted rats could account for known changes in antral endocrine cell function.

Animals↗

PubMed1996

Gastric endocrine cells: gene expression, processing, and targeting of active products.

Endocrine cells of the gastric epithelium secrete biologically active peptides and small messenger molecules such as histamine, serotonin, and gamma-aminobutyric acid. The secretory products may act locally (paracrine or autocrine effects) or at distant targets after delivery in the circulation (hormonal effects). the contents of the gastric lumen control both secretion of gastric endocrine cells and the expression of genes involved in the synthesis of their active secretory products; in some cases, gene regulation may occur over periods as short as that required for digestion of a single meal. The conversion of inactive peptide precursors to their active forms takes place during transit along the secretory pathway and is only completed after sequestration in secretory granules. the processing of the gastrin precursor provides a useful model for studying prohormone processing. Generation of the well-known amidated gastrins requires prohormone cleavage and COOH-terminal amidation; the products stimulate acid secretion and mucosal growth. However, recent work indicates that biosynthetic intermediates that do not stimulate acid secretion may nevertheless act at a novel receptor to stimulate growth, so that control of prohormone processing determines which of two alternative types of biologically active peptide is released by gastrin cells. Gastric endocrine cells also have the capacity to accumulate small messenger molecules in secretory vesicles, via proton exchangers. Recent work indicates physiological regulation of the expression of genes encoding cytosolic enzymes such as histidine decarboxylase, which converts histidine to histamine, and of secretory granule transporters such as vesicular monoamine transporter type 2, which concentrates amines in secretory vesicles. Together these findings suggest that modulation of regulatory peptide and amine biosynthesis in gastric endocrine cells constitutes a primary response of the stomach to the arrival of a meal.

Amino Acid Sequence↗

PubMed1995

Estimate of net calcium fluxes and sarcoplasmic reticulum calcium content during systole in rat ventricular myocytes.

1. The experiments were performed on voltage-clamped cells in which intracellular calcium concentration ([Ca2+]i) was measured with the fluorescent indicator indo-1 (acetoxymethyl ester (AM) loading). When cells were stimulated with a short (100 ms) depolarizing pulse, following a rest, the magnitude of the first systolic calcium transient was greater than that in the steady state (rest potentiation) and decayed to its steady level over a few stimuli. If a longer pulse (800 ms) was used then the systolic calcium transient was either unaffected or increased in magnitude following a rest. During constant stimulation, if the length of the pulse is decreased, then the magnitude of the calcium transient decreased reversibly over several beats. 2. The calcium entry into the cell was measured from the integral of the inward calcium current and the efflux from the Na(+)-Ca2+ exchange current on repolarization. During the negative staircase the calcium current was approximately constant whilst the Na(+)-Ca2+ exchange current decayed in parallel with the systolic calcium transient. A net loss of calcium from the cell can be calculated from the extra Na(+)-Ca2+ exchange current following the initial pulses. 3. The application of caffeine produces a transient increase of both [Ca2+]i and an inward Na(+)-Ca2+ exchange current. The integral of this current can be used to estimate the caffeine-releasable calcium content of the sarcoplasmic reticulum (SR), which decreases following stimulation with short compared to long pulses. This difference in SR calcium content is quantitatively similar to that estimated from the sarcolemmal currents. 4. At a given membrane potential, the relationship between [Ca2+]i and current during the caffeine exposure can be used to estimate the Na(+)-Ca2+ exchange flux from the measured [Ca2+]i and thence the Na(+)-Ca2+ exchange flux during depolarization. 5. For a long depolarizing pulse the extrusion of calcium from the cell on Na(+)-Ca2+ exchange is comparable to the entry on the calcium current. In contrast, for short pulses the extrusion of calcium on the Na(+)-Ca2+ exchange immediately after the pulse is greater than the entry during the pulse on the calcium current. 6. These results show that rest potentiation can be correlated with changes in the amount of calcium stored in the SR and this, in turn, can be accounted for by sarcolemmal fluxes.

Animals↗

PubMed1995

Pathways of processing of the gastrin precursor in rat antral mucosa.

The precursor of the acid-stimulating hormone gastrin gives rise to multiple peptides differing markedly in biological activity, but the relevant biosynthetic pathways are poorly understood. We have used antibodies to amidated gastrins, gastrins with COOH-terminal glycine (Gly) gastrins with COOH-terminal hydroxyglycine (GlyOH) and to the COOH terminus of progastrin, to immunoprecipitate peptides labeled with [35S]sulfate or [3H]tyrosine during incubation of rat antral mucosa in vitro. Labeled progastrin was detectable after 30 min of continuous incubation with isotopic precursors, G34 and G34-Gly after 60 min, and G17 and G17-Gly after 120 min. Pulse chase experiments indicated that progastrin is converted to G34-Gly which then follows one of two pathways: (a) hydroxylation of COOH-terminal Gly and conversion to G34 followed by cleavage yielding G17, or (b) cleavage to G17-Gly. The kinetics of G17-Gly and G17 labeling were similar, suggesting that G17-Gly is a product in its own right, and not simply an intermediate in G17 synthesis. Since the two peptides are reported to have distinct biological activities, they appear to be alternative mature products of progastrin processing.

Animals↗

PubMed1995

Classification of positive inotropic actions based on electrophysiologic characteristics: where should calcium sensitizers be placed?

A number of new positive inotropic agents with diverse mechanisms of action have been discovered over the past 20 years. Most of these cardiotonic drugs exhibit characteristic electrophysiologic profiles. This prompted us to propose a classification scheme based on electrophysiologic principles, modifying the categories recently suggested by another author. Class I actions designate positive inotropic mechanisms that enhance the transmembrane calcium current by various means, such as beta-receptor stimulation (dobutamine, class I/A), phosphodiesterase inhibition (milrinone, class I/B), direct stimulation of adenylate cyclase (forskolin, class I/C), or direct modulation of calcium channel gating (BAY K 8644, class I/D). Class II action includes mechanisms that lead to elevation of intracellular sodium activity either by inhibiting the Na,K pump (digitalis, class II/A) or by increasing transmembrane sodium influx (DPI 201-106, class II/B). Class III action involves a mechanism by which sensitivity of the myofilaments to calcium increases (EMD 53998, levosimendan). This mechanism is not associated with apparent electrophysiologic manifestations. Positive inotropism due to lengthening of the cardiac repolarization (almokalant) is considered as class IV action. The possible clinical implications of the various positive inotropic mechanisms are also discussed.

Animals↗

PubMed1994

Discrimination between temperature- and brefeldin A-sensitive steps in the sulfation, phosphorylation, and cleavage of progastrin and its derivatives.

Maturation of the acid-stimulating hormone gastrin involves precursor cleavage, tyrosine sulfation, serine phosphorylation, and COOH-terminal amidation. We have used brefeldin A and incubation at 22 degrees C to determine where and when these modifications occur. Immunogold studies of gastrin cells incubated at 22 degrees C revealed swollen Golgi cisternae, the terminal regions of which were associated with an accumulation of progastrin immunoreactivity. At 22 degrees C, [3H]tyrosine and [35S]sulfate were incorporated into progastrin, but Arg94-Arg95 cleavage, and Ser96 phosphorylation, were inhibited. When pulse labeling at 22 degrees C for 120 min was followed by a chase at 37 degrees C, [35S]progastrin was cleaved at Arg94-Arg95 with a t1/2 of about 10 min, compared with about 20 min for [3H]progastrin. Approximately 60% of the COOH-terminal cleavage fragment was phosphorylated, but there was little or no incorporation of [32P]phosphate into progastrin. Addition of brefeldin A during the chase substantially inhibited cleavage of [3H]progastrin, but not [35S]progastrin. However, when pulse labeling was limited to 20 min at 22 degrees C, the presence of brefeldin A in a subsequent chase at 37 degrees C completely inhibited cleavage of [35S]progastrin. The data indicate that progastrin sulfation occurs in the trans-Golgi network, exit from which involves passage through first a brefeldin A-sensitive and then a temperature-sensitive step. Cleavage at Arg94-Arg95 and Ser phosphorylation are closely linked, occur distal to the temperature-sensitive step, and are followed by amidation in secretory granules. It is known that mature secretory granules do not phosphorylate progastrin-derived peptides, and so phosphorylation appears to coincides with, and may provide a marker for, delivery of peptide from trans-Golgi work to immature secretory granules in gastrin cells.

Amides↗

PubMed1994

Cholecystokinin in cortico-striatal neurons in the rat: immunohistochemical studies at the light and electron microscopical level.

Using immunohistochemical techniques we have analysed the occurrence of cholecystokinin-like immunoreactivity (CCK-LI) in the cortex and striatum of the rat. In the cortex few CCK-immunoreactive cell bodies, mainly interneurons, could be visualized in normal brains, and a moderately dense network of CCK fibres was also observed. Injections of colchicine into the striatum led to an accumulation, in the surrounding cortex, of CCK-LI in the initial segment of the axon of numerous cells. In addition, with an antibody to pro-CCK several cell bodies, many of which with pyramidal shape, could be visualized. Furthermore, retrograde staining of cortical cells after unilateral injection of wheat germ agglutinin into the striatum revealed bilaterally in the cortex a number of labelled cells that also contained pro-CCK-LI. In the striatum CCK-LI was diffusely distributed in fine fibres as well as in patches of fibres located in the medial aspects. After decortication followed by callosotomy these patches disappeared on the side ipsilateral to the lesion, while the pattern of immunoreactivity of several other peptides in the striatum was unaffected. No change was observed on the contralateral side. Decortication or callosotomy alone did not affect the pattern of CCK-LI. At the ultrastructural level several CCK-immunoreactive terminals could be observed, mostly with clear, densely packed vesicles and straight asymmetric synaptic contacts with small spines, characteristic for terminals of cortical origin. The results are consistent with the presence of a major, partly crossed, CCK-containing cortico-striatal pathway.

Animals↗

PubMed1994

Phosphorylation of human preprogastrin 93-101 by a Golgi membrane kinase from rat mammary gland.

The precursor of the acid-stimulating hormone gastrin contains a phosphorylation site which is immediately adjacent to a functionally important cleavage site, and which occurs in a sequence resembling the phosphorylation sites in casein. We have examined phosphorylation of human preprogastrin 93-101 with [gamma-32P]ATP by a Triton-solubilized Golgi membrane preparation from mammary glands of lactating rats. The activity of solubilized Golgi membranes was approx. an order of magnitude greater than that of intact vesicles suggesting a luminal orientation of the kinase. Incorporation of 32P was linear for up to 12 min at 30 degrees C, and the half-maximal rate of phosphorylation at 1 mM ATP was observed at peptide concentrations of 0.2 mM. The Km for ATP was 0.12 mM and the maximal velocity was 2.17 nmol of peptide per min per mg Golgi protein. Proteinase inhibitors (leupeptin, pepstatin, benzamidine) and p-nitrophenyl phosphate did not influence phosphorylation. The incorporation of 32P was inhibited by poly-L-lysine but not by heparin. We conclude that the phosphorylation site in progastrin is a substrate for a Golgi membrane kinase and that a similar enzyme might act on endogenous progastrin in vivo.

Amino Acid Sequence↗

PubMed1993

Post-translational processing of progastrin: inhibition of cleavage, phosphorylation and sulphation by brefeldin A.

The precursor for the acid-stimulating hormone gastrin provides a useful model for studies of post-translational processing because defined sites of cleavage, amidation, sulphation and phosphorylation occur within a dodecapeptide sequence. The factors determining these post-translational processing events are still poorly understood. We have used brefeldin A, which disrupts transport from rough endoplasmic reticulum to the Golgi complex, to examine the mechanisms of cleavage, phosphorylation and sulphation of rat progastrin-derived peptides. Biosynthetic products were detected after immunoprecipitation using antibodies specific for the extreme C-terminus of progastrin, followed by reversed-phase and ion-exchange h.p.l.c. Gastrin cells incorporated [3H]tyrosine, [32P]phosphate and [35S]sulphate into both progastrin and its extreme C-terminal tryptic (nona-) peptide. Ion-exchange chromatography resolved four forms of the C-terminal tryptic fragment of progastrin which differed in whether they were phosphorylated at Ser96, sulphated at Tyr103, both or neither. The specific activity of [3H]tyrosine in the peak that was both phosphorylated and sulphated was higher than in the others. Brefeldin A inhibited the appearance of [3H]tyrosine-labelled C-terminal tryptic fragment but there was an accumulation of labelled progastrin and a peptide corresponding to the C-terminal 46 residues of progastrin. Brefeldin A also inhibited incorporation of 32P and 35S into both progastrin and its C-terminal fragment. Thus phosphorylation of Ser96, sulphation of Tyr103 and cleavage at Arg94-Arg95 depend on passage of newly synthesized progastrin along the secretory pathway; as brefeldin A is thought to act proximal to the trans-Golgi, these processing steps would appear to occur distal to this point. The data also indicate that the stores of unphosphorylated C-terminal tryptic fragment are not available for phosphorylation, implying that this modification occurs proximal to the secretory granule; cleavage is known to occur in the secretory granule which suggests that it occurs after phosphorylation.

Animals↗

PubMed1993

An estimate of the calcium content of the sarcoplasmic reticulum in rat ventricular myocytes.

The aim of this paper was to estimate the Ca content of the sarcoplasmic reticulum (s.r.) and to compare this with the amount of Ca which enters the cell via the calcium current in systole. The s.r. Ca content was measured electrophysiologically in voltage-clamped rat ventricular myocytes. Rapid application of caffeine produced a transient increase of [Ca2+]i which was accompanied by a transient inward Na-Ca exchange current. The integral of this current gives a measure of the Ca2+ pumped out of the cell by Na-Ca exchange. Ni2+ (5 mM) inhibited the current and decreased the rate of fall of [Ca2+]i to 32% of the control suggesting that Na-Ca exchange is responsible for 68% of Ca removal from the cytoplasm following the addition of caffeine. Correcting for the Na-Ca independent Ca removal suggests that the s.r. Ca content is equivalent to about 120 mumol per litre cell. Furthermore we estimate that, during systole, Ca entry into the cell via the sarcolemmal calcium current is equal to about 6% of the Ca content of the s.r.

Animals↗

PubMed1993

Caffeine-induced decreases in the inward rectifier potassium and the inward calcium currents in rat ventricular myocytes.

The effects of high (20 mM) concentrations of caffeine were studied on the transmembrane voltage and currents in rat single ventricular myocytes by the whole cell configuration of the patch clamp technique. Rapid application of caffeine released Ca2+ from the sarcoplasmic reticulum and induced a Ni(2+)-sensitive transient inward current with concomitant change of the transmembrane voltage from -72.6 +/- 0.4 to -68.0 +/- 0.6 mV (n = 4). Maintained application of caffeine lengthened the action potential duration (APD90) from 66.7 +/- 16.9 to 135.1 +/- 34.1 ms (n = 4) and depressed the amplitude of both the inward rectifier potassium and the inward calcium currents. It is concluded that these effects of caffeine should be recognized when it is used as a tool to study electromechanical coupling.

Action Potentials↗

PubMed1993

Control of tissue progastrin concentrations in the rat.

The influence of different physiological stimuli on plasma concentrations of the acid-stimulating hormone gastrin and on the tissue concentrations of its precursor, progastrin, were examined in the conscious rat. Plasma concentrations were measured by radioimmunoassay using antibody specific for the C-terminus of biologically active (amidated) gastrins, and tissue concentrations of progastrin were measured after size exclusion chromatography by radioimmunoassay using antibody specific for the C-terminus of rat progastrin. Plasma and antral tissue were taken from control rats fed ad libitum, from rats fasted for 48 h, and from fasted or fed rats treated with the proton pump inhibitor omeprazole to reduce acid-induced inhibition of gastrin release. Plasma gastrin concentrations were depressed 4-fold by fasting and this was reversed by treatment with omeprazole; in rats fed ad libitum and treated with omeprazole plasma gastrin was elevated 8-fold. Fasting did not significantly change the plasma clearance of gastrin, indicating that changes in endogenous circulating levels are attributable to altered secretion rather than metabolism. Tissue progastrin concentrations were depressed 3-fold in fasted rats compared with rats fed ad libitum. Treatment of fasted rats with omeprazole produced a 2-fold increase in tissue progastrin; but in spite of the substantial elevation of plasma gastrin in fed rats treated with omeprazole, tissue progastrin was elevated by only about 50%. Sulphation at Tyr103 of progastrin was not changed by fasting or omeprazole. An estimate of the conversion of progastrin to amidated gastrin was determined as the tissue progastrin clearance, i.e. the weight of antral mucosa in which progastrin is converted to amidated gastrin and secreted per minute to maintain plasma concentrations. Conversion rates were increased 7-fold in fed omeprazole-treated rats compared with controls; in fasted rats treated with omeprazole the rate of conversion was depressed 50% compared with controls. It is concluded that changes in the lumen of the stomach are able to influence the processes by which progastrin is converted to its active amidated products.

Amino Acid Sequence↗

PubMed1993

Identification of progastrin derived peptides in colorectal carcinoma extracts.

The possible production of gastrin by colorectal carcinomas has been studied. Extracts of 44 tumours and adjacent macroscopically normal tissue were examined in radioimmunoassay using the following antibodies: (i) L289 raised to a C-terminal fragment of progastrin which shows specificity for intact progastrin, but not the extreme C-terminal tryptic peptide; (ii) LW60 raised to a C-terminal fragment of progastrin which reacts with progastrin and its C-terminal tryptic peptide; (iii) 109-21 which was raised to, and reacts with, Gly-extended forms of heptadecapeptide gastrin--that is, biosynthetic intermediates on the pathway producing active gastrin; and (iv) L2 which reacts with amidated, biologically active gastrins. All samples contained detectable material in assays using LW60; in general, concentrations measured with this antibody were higher than with the other antibodies, and in particular there were higher concentrations in tumour compared with normal tissue extracts. Tumour extracts also contained higher concentrations of immunoreactivity compared with normal tissue, in assays using antibodies L289 and 109-21. In contrast, amidated gastrins were found in similar concentrations in tumour and normal tissue, and concentrations were the lowest of those recorded in the four assays. Separation on Sephadex G50 revealed peaks compatible with progastrin and its C-terminal flanking peptide, and two other peaks that are so far unidentified. In conclusion most colorectal carcinomas contain peptides derived from the gastrin precursor, progastrin, but for the most part these tumours do not convert progastrin into biologically active products.

Amino Acid Sequence↗