Differential distribution of molecular forms of cholecystokinin in human and porcine small intestinal mucosa

To examine the distribution of cholecystokinins (CCKs) along the small intestine we examined the nature of CCKs in samples of jejunum, mid-intestine and ileum from human and porcine intestine. CCKs in intestinal mucosa were extracted by boiling in both neutral and acid conditions, and subjected to high pressure liquid chromatography (HPLC) to separate the forms of CCK followed by radioimmunoassay of separate fractions. In neutral extracts of human intestine CCK immunoreactivity totalled 119.4, 22.9 and less than 1 ng/g in jejunum, mid-intestine and ileum, whilst in acid extracts the corresponding values were 65.3, 47.4 and less than 1 ng/g. Amounts of CCK extracted from porcine mucosa were of similar magnitude. In neutral extracts material co-chromatographing on HPLC with synthetic porcine CCK 8 predominated, whilst in acid extracts material co-chromatographing with CCKs 33/39 was the major form. These forms of human and porcine CCKs extracted from the mucosa behaved similarly to CCK 8 and CCK 33/39 standards on HPLC, in the radioimmunoassay and on molecular exclusion chromatography - suggesting marked similarity of the CCKs in the two species. In both species there was a marked change in the ratios of CCK 8: CCK 33/39 down the intestine from 1: 0.8 in human jejunum to 1: 5.6 in mid-intestine and from 1: 1.5 in porcine jejunum to 1: 5.8 in mid-intestine. These observations may explain the changing patterns of CCKs in circulation with time after ingestion of a fat meal and the greater impairment of CCK 8 than CCK 33/39 release observed in coeliac disease.

Measurement and occurrence of sulfated gastrins

Sulfated gastrins resemble cholecystokinins (CCK) both structurally and functionally. They are less potent than CCK in stimulating gallbladder contraction and pancreatic enzyme secretion, but the plasma concentrations of sulfated gastrin are higher than those of CCK. Therefore, sulfated gastrins may contribute significantly to the endogenous CCK activity. The degree of sulfation of gastrin differs with the localization in the digestive tract. In the antrum and duodenum of normal subjects 45% of the gastrins are sulfated, as in serum. In contrast, the sulfation of gastrin is complete in the jejunum (human) and in the pancreas (rat and cat). Hence, the degree of sulfation of gastrin is similar to that of CCK in the jejunum. The degree of sulfation in antrum, duodenum and serum diminishes with hypergastrinemia, and is thus significantly lower in patients with gastric ulcer or pernicious anemia than in healthy subjects. In the Zollinger-Ellison syndrome, the degree of sulfation of gastrin varies greatly (20-90%) and the distribution between small and large gastrins is equally variable. However, sulfation and proteolytic processing follows a parallel course; complete processing to smaller components is accompanied by complete sulfation of the peptide and vice versa. During ontogenesis sulfated gastrins may be of special importance, since they are the only sulfated members of the gastrin/CCK family of peptides which occur in substantial quantities in the early fetus. Tyrosine-O-sulfation has now been recognized as a widespread modification, and sulfated tyrosyl residues in gastrin, CCK and leu-enkephalin are examples of a derivatization which can govern the biological activity of regulatory peptides.

Pregnancy-associated alpha 2-glycoprotein (alpha 2-PAG) and IgA: their parallel distribution in the human gastrointestinal tract

Using a combined immunoperoxidase (PAP)/direct immunofluorescence (IF) staining technique, pregnancy-associated alpha 2-glycoprotein (alpha 2-PAG) has been shown to be present in the majority of IgA-producing plasma cells in the lamina propria of both the jejunum and the colon. Both proteins have also been detected on the apical surface of columnar epithelial cells, particularly in the colon, and it is suggested that alpha 2-PAG, like IgA, may be secreted into the lumen of the gastrointestinal (GI) tract by an active transport mechanism. The concentration of alpha 2-PAG in the jejunal fluid of most subjects was found to be less than 20 micrograms/liter, although a number of subjects showed substantially elevated levels. The significance of the association between IgA and alpha 2-PAG, which is known to have immunosuppressive properties, is discussed in relation to the requirement for an efficient immunologic barrier within the GI tract.

Proton nuclear magnetic resonance studies of porcine intestinal calcium binding protein

1H nuclear magnetic resonance has been employed to study the environment of several proton nuclei (primarily those arising from aromatic residues) of the porcine intestinal calcium binding protein. An assignment for the single tyrosine (Tyr-16) residue has been made on the basis of laser photochemically induced dynamic nuclear polarization (CIDNP) and mononuclear decoupling experiments. pH titration studies have shown that the tyrosine pKa is unusually high in the apoprotein and increases even further upon the addition of calcium. However, the observation of a CIDNP effect with this tyrosine in both the presence and absence of calcium indicates that it is solvent accessible and therefore exposed on the surface of the molecule. Under the conditions of these experiments, the protein was observed to bind calcium with a 2:1 stoichiometry, at a rate of exchange slow enough that the NMR spectra are in the slow-exchange limit. The presence of upfield shifted phenylalanine and methyl resonances in the apoprotein indicates that there is a well-defined tertiary structure in the absence of calcium.

Molecular forms of glucagon-like immunoreactivity in porcine intestine and pancreas

Glucagon-related polypeptides in porcine pancreas and intestine were analysed by gel-permeation chromatography and RIA. Three assays were employed: a nonspecific glucagon assay (R59) of 94% cross-reactivity with glicentin; a pancreatic glucagon assay (RCS5) directed against the C-terminal region of glucagon and of less than 0.01% cross-reactivity with glicentin; and a glicentin assay (R64) of less than 0.01% cross-reactivity with glucagon. For extracts of porcine pancreas all three assays gave similar molar concentrations of immunoreactivity. In porcine intestinal extracts immunoreactivity was detected in significant amounts only by the nonspecific glucagon (R59) and the glicentin (R64) assays, again in similar molar concentrations. The immunoreactivities present in pancreas and intestine were chromatographically and immunologically separable into six main peaks, peaks I, II, III, V, and VI being present in the pancreas, and peaks I, II, and IV in the intestine. The different immunoreactivities of the peaks allowed probable identities to be assigned to their main components. Apart from peak I, which consists of void-volume material that may interfere nonspecifically with the assays, the main components of the peaks can be interpreted as glicentin (in peak II) or fragments derived from glicentin. Peak III contains the N-terminal portion of glicentin (glicentin-related pancreatic peptide), peak IV probably contains glucagon with its 8 amino-acid C-terminal extension, peak V is pancreatic glucagon and peak VI contains smaller N-terminal glicentin fragments. These findings fit with the proposition that glicentin fulfills the role of proglucagon in the pancreas, and is the major component of enteroglucagon in the intestine.

Effect of antrectomy on small intestinal structure and function in the rat

Antrectomy reduced the levels of circulating gastrin but did not change jejunal morphology. In vitro and in vivo absorption as well as the activity of some brush border enzymes were increased. The observed alterations are discussed on the basis of antrectomy-induced alterations in the release of gastrointestinal hormones, gastric and pancreatic secretion and gastric emptying.

Isolation of glucagon-37 (bioactive enteroglucagon/oxyntomodulin) from porcine jejuno-ileum. Isolation of the peptide

A 37 amino acid-peptide has been isolated from porcine jejuno-ileum on the basis of its glucagon-like activity in liver (interaction with glucagon-binding sites and activation of adenylate cyclase) using gel filtration, ion-exchange and high-performance liquid chromatography. Depending on the criteria chosen, this peptide is referred to as either 'bioactive enteroglucagon' (activity in liver), 'oxyntomodulin' (specific action in gastric oxyntic glands) or 'glucagon-37' (chemical structure).

d-Glucose balance in the enterocyte of rat jejunum "in vitro"

An everted sac of male albino rat jejunum (Wistar strain) incubated "in vitro" in used. Net d-glucose and Na+ transport together with d-glucose concentration in the emerging fluid [5], or in ths serosal fluid, and in the enterocytes are determined. Cell d-glucose concentration does not change significantly in a range between 20-200 mumoles or between 50-500 mumoles of net d-glucose transepithelial transport, depending on the experimental conditions. As far as cellular d-glucose and Na+ concentration is concerned, the enterocyte behaves as an homeostatic system. The mechanism involved in d-glucose extrusion is extensively discussed. Two hypothesis seem to be possible. First, the mechanism is an active metabolically dependent one, just as it is for sodium transport. Second, the metabolic activity favours d-glucose facilitated permeability through the basolateral membrane in such a way as to maintain a constant relationship between d-glucose and Na-extrusion, notwithstanding the fact that d-glucose concentration gradient across the basolateral membrane lowers by increasing Na and glucose extrusion rate.

Intestinal thiamin transport in rats. Thiamin and thiamin phosphoester content in the tissue and serosal fluid of everted jejunal sacs

Rat everted jejunal sacs were incubated at 37 degrees C for 15-60 min in Krebs-Henseleit buffer, pH 7.4, with or without (control experiments) 0.2 microM [thiazole-2-14C]-thiamin. The determination of thiamin and its phosphoesters in the sac wall and in serosal fluid was carried out by an electrophoretic micromethod. Irrespective of the presence of 14C-thiamin, the tissue content of endogenous thiamin pyro- and triphosphate decreased during the incubation, whilst that of thiamin-monophosphate remained relatively constant. The tissue content of free thiamin increased substantially only in control experiments. Endogenous free thiamin, together with a small amount of monophosphate, was found to enter the serosal fluid. The transfer of both compounds was greatly enhanced by the incubation with 14C-thiamin, when an efficient thiamin phosphorylation could be demonstrated. During incubation with 14C-thiamin, the concentration of 14C-thiamin-pyrophosphate and, to a lesser extent, that of free 14C-thiamin increased progressively in the tissue, while 14C- thiamin-monophosphate content remained almost unchanged. No 14C-thiamin-triphosphate was detected. There was a rapid increase in the tissue specific radioactivity of free thiamin and thiamin-monophosphate, which preceded the rise in the specific radioactivity of thiamin-pyrophosphate. The specific radioactivities of the former compounds in the serosal fluid reflected those observed in the intestinal tissue. These results are interpreted as evidence suggesting that the active transport of thiamin is efficient only when intracellular thiamin phosphorylation is operating.

Differences in sulfated glycosaminoglycans composition of the gastrointestinal mucosa

Sulfated glycosaminoglycan (SGAG) composition of normal mucosa of esophagus, gastric body, antrum, duodenum, jejunum and rectum is reported. Each region examined may be defined by specific sulfated glycosaminoglycan distributions showing variations in relative proportions and total amount of heparan sulfate, dermatan sulfate and chondroitin 4, 6-sulfate. The results are discussed in the light of a recent proposal regarding the role of these compounds in cell-cell recognition and stimulation of cell division. The methodology made it possible to detect sulfated glycosaminoglycans from small amounts of tissue obtained by endoscopic biopsies.

Glycosphingolipids of rat tissues. Different composition of epithelial and nonepithelial cells of small intestine

The epithelial cells of rat small intestine (jejunum-ileum) were separated from their supporting stroma (residue). Total nonacid and acid glycosphingolipids were prepared from the two compartments. The acetylated nonacid glycolipids were separated into 10-12 fractions by column chromatography. These were analyzed by chromatographic methods, mass spectrometry, and proton NMR spectroscopy and compared with glycolipids isolated from whole rat small intestine. The sialic acid-containing glycosphingolipids were compared in the same way without subfractionation. At least 37 different glycosphingolipids (different carbohydrate moieties) were found, 23 in the nonepithelial residue and 17 in the epithelial cells of one rat strain. In a second rat strain, another 4 structures were detected. The glycosphingolipids of epithelial cells and nonepithelial residue were distinctly different. Glucosylceramide, lactosylceramide, and globotriaosylceramide were found in both compartments, while isoglobotriaosylceramide was restricted to the nonepithelial residue. A tetrahexosylceramide with a terminal Gal alpha 1 leads to 3 on a globotriaosylceramide core was found in both compartments as were homologues with 1 or 2 additional internal leads to 3Gal alpha 1 leads to units, but homologues with 3 or 4 additional internal Gal were only nonepithelial. Glycosphingolipids with terminal beta-GalNAc were restricted to the nonepithelial residue comprising globotetraosylceramide, isoglobotetraosylceramide, and a series of glycolipids with 5 to 9 sugars having the above-mentioned oligohexosylceramides as core structures. Fucolipids (blood group H) having 3, 5, 6, and 7 sugars and lacking amino sugars, and fucolipids with 5 and 10 sugars containing N-acetylglucosamine were restricted to the epithelial cells. Fucolipids (blood groups H and B) with 5 and 6 sugars containing N-acetylgalactosamine were restricted to the nonepithelial residue. In a 4, 6, and 12 sugars were found in the epithelial cells. N-Glycoloylneuraminosyllactosylceramide was the only ganglioside found in the epithelial cells while N-acetylneuraminosyllactosylceramide was nonepithelial together with gangliosides based on gangliotetraosylceramide and isoglobotetraosylceramide.

Mucosal enzyme activities, peptide hormone concentrations and hormone secretory granule properties in functioning proximal jejunum after shunt operation for obesity

Crosby capsule biopsies were obtained from functioning jejunum in 6 patients between 7 and 15 months after jejuno-ileal for morbid obesity and compared with 6 normal control biopsies. Brush border and other mucosal enzyme activities and seven regulatory peptide concentrations were measured in each biopsy. Analytical subcellular fractionation by sucrose density gradient centrifugation was used to investigate brush border and peptide secretory granule properties. Specific activities of all the brush border enzymes assayed in the bypass patients were similar to the normal controls and subcellular fractionation studies showed no change in brush border properties. Similarly, properties of other mucosal organelles and their associated enzyme activities were unchanged in the bypass patients. The mucosal regulatory peptide concentrations in the bypass patients showed no significant difference from the normal controls and no changes were detected in peptide storage granule properties. These studies therefore support the concept that the adaptive changes occurring after jejuno-ileal bypass are due to changes in cell numbers or other parameters of function rather than changes in the specific activities of the brush border enzymes themselves. They also show that the marked abnormalities of plasma hormone release after bypass surgery are not in themselves due to alterations in mucosal hormone concentrations, or of the secretory granule properties.

Endoplasmic reticulum membrane isolated from small-intestinal epithelial cells: enzyme and protein components

Endoplasmic reticulum membrane-rich fraction was obtained by subfractionation of the light microsomes from mouse jejunal mucosal epithelial cells. It was marked by high glucose-6-phosphatase, NADPH-cytochrome c reductase, and NADH-cytochrome c reductase activities and low Na+,K+-ATPase activity. The enrichment of Na+,K+-ATPase was 180-fold higher in the basolateral membranes than in the endoplasmic reticulum membrane-rich fraction relative to glucose-6-phosphatase. The protein peak that was phosphorylated in a Na-dependent manner was prominent in the basolateral membranes while it was a minor peak in the endoplasmic reticulum membrane-rich fraction. Under the electron microscope the fraction was seen to be composed of homogeneous small vesicles with thin smooth membranes.

Distribution of Fc gamma receptors on isolated gut enterocytes of the suckling rat

An erythrocyte-antibody rosette assay has been used to study the presence and distribution of Fc gamma receptors on enterocytes isolated from 12-day-old suckling rat gut by means of a buffer medium containing EGTA. Such receptors were found to be restricted to enterocytes in the proximal region (duodenum and jejunum) of the small intestine and to be acid-pH dependent. For the majority of enterocytes indicator red cells bound in high density to the abluminal plasmalemma but not to the apical microvillous brush border. Since immunofluorescence studies revealed strong binding of added IgG to the microvillous region, a likely explanation is that there is a paucity of Fc gamma receptors from the tips of microvilli (at least under the conditions of the rosette assay) and that receptors more deeply situated as inaccessible to indicator red cells. Binding of indicator red cells was readily inhibited by rabbit, human, guinea pig and rat IgG but less so by bovine IgG, and of the two sub-classes, bovine IgG2 inhibited much more readily than bovine IgG1. Cortisone acetate injection virtually abolished Fc gamma receptor expression on isolated enterocytes within three days. These findings correlate both with selective transport of IgG of different species in vivo and the known effect of cortisone acetate to terminate such transport.

[Bioactive "enteroglucagon" (oxyntomodulin): evidence for a C-terminal extension of the glucagon molecule]

The bioactive fraction of "enteroglucagon" has been isolated from the porcine jejuno-ileum on the basis of its glucagon-like action in liver. High performance liquid chromatography analysis followed by Dansylation of peptide fragments obtained after enzymatic digestion of both this peptide and glucagon suggests that the bioactive "enteroglucagon" contains the glucagon molecule plus a C-terminal extension under the from of the octapeptide. Lys-Arg-Asn-Lys-Asn-Asn-Ile-Ala-COOH. The presence in the native molecular of a structural difference of modification as compared to glucagon in the 1-11 fragment is possible.

Determination of transferrin-like immunoreactivity in the mucosal homogenate of the duodenum, jejunum, and ileum of normal and iron deficient rats

1. In intestinal mucosal tissue a transferrin-like immunoreactivity (TLIR) was determined after loading with 59Fe-(FeCl3) in vivo. The scraped-off mucosal tissue was homogenized and centrifuged at 100 000 X g. The supernatant was fractionated chromatographically. The TLIR was determined by the Mancini-test. 2. Extrapolated to infinite dilutions of the homogenate the following contents of the TLIR were calculated per cm of the intestinal segment: 28, 20, and 13, microgram/cm in the duodenum, jejunum, and ileum of iron-deficient animals and 15, 14, and 12 microgram/cm in the corresponding intestinal segments of normal rats, respectively. 3. The content of TLIR was compared with the iron uptake of the mucosal tissue from the intestinal lumen during absorption. An "iron turnover number" of 1.6 +/- 0.2 iron atoms per min during the absorption in duodenal and jejunal segments and of 0.5 +/- 0.1 in ileal segments of either iron-deficient and normal animals was calculated for the mucosal transferrin represented by the TLIR.

Studies on hydragogue drugs: effect of surfactants on cAMP levels in the rat jejunal mucosa in short time experiments in vivo

Theophylline and the surface active agents specified below were instilled into the jejunum of anaesthetized rats, and the cAMP levels in the mucosal tissue determined after 71/2 and 15 min. incubation in vivo. Most experiments were done in rats prepared with two tied intestinal loops; one of these served as the control loop and the other as the stimulated loop. The surfactants (mmol/l) included dodecylsulphate (17), dioctylsulphosuccinate (5.6), cetrimonium bromide (4.1), deoxycholic acid (2.4 and 3.6) and Lubrol WX (0.5% w/v). Theophylline (10 mmol/l) caused a substantial increase in cAMP (110% +/- 17, n = 7 and 60% +/- 8.9, n = 10, respectively) and dodecylsulphate a minor and transitory increase (28.1% +/- 3.8, n = 10 and 11.7% +/- 4.9, n = 8). The other agents were without stimulatory effect on cAMP, although like dodecylsulphate they may significantly affect normal intestinal cation and glucose transport under these conditions. The results, therefore, do not suggest that stimulation of cAMP and intestinal secretion induced thereby is any significant phenomenon in the overall hydragogue effect of these agents, at least not in short term jejunal experiments.

High interferon titer in newborn pig intestine during experimentally induced viral enteritis

We looked for the presence of interferon in the digestive tract of newborn piglets infected with a virulent strain of transmissible gastroenteritis virus (Coronaviridae). High levels of type 1 interferon activity were found early in the disease in jejunal and ileal parts of the intestine as well as in the serum. Enterocytes appeared to be involved in the interferon synthesis. These findings raise the question of the role of interferon in the pathogenesis of viral enteritis.

Glucagon in spontaneously diabetic KK mice

In order to investigate the relationship between the development of diabetes mellitus and glucagon, experimental studies were performed in genetically diabetic mice (KKA gamma and KK B1) and in C57 mice of various ages. In the KK mice, the fasting plasma glucose increased during the aging process and reached the maximum at 14 weeks. The fasting plasma insulin in the KK mice was significantly elevated during the aging process and continued to increase till 20 weeks of age. In contrast, an increase in the fasting plasma glucagon was observed only at the age of 4 weeks, although the plasma glucagon increased during the aging process. The content of the insulin in the pancreas of the KK mice was significantly higher than that of the C57 mice, continuing to increase during the aging process. the glucagon content of the pancreas increased during the aging process but no significant difference was observed between the KK mice and the control mice. The total immunoreactive glucagon in the jejunum measured by non-specific antiserum was slightly reduced in the KK mice at the age of 14 weeks, compared with the C57 mice. There was no difference in the glucagon content of the stomach between the KK mice and the C57 mice of various ages. The KK mice at 14 weeks showed an elevated plasma glucagon 30 min after glucose injection, compared with the C57 mice, which indicates a reduced suppression of glucagon in response to hyperglycemia in the KK mice. The plasma glucagon in the KK mice 30 min after arginine was slightly higher than in the control mice, although not significantly so. From these results it was concluded that the KK mice revealed an elevation of fasting plasma glucagon in the early stage of diabetes mellitus and a decrease in glucose-induced glucagon suppression at 14 weeks and that diabetes mellitus in the KK mice derived mainly from insulin resistance associated with hyperinsulinemia.

Bioactive enteroglucagon (oxyntomodulin): present knowledge on its chemical structure and its biological activities

A bioactive form of enteroglucagon has been isolated from porcine jejuno-ileum according to its glucagon-like effect in liver. Enzymatic digestion followed by HPLC, dansylation and partial sequence analysis strongly suggests that this peptide contains the glucagon molecule (1--29) elongated at the C-terminal end by the octapeptide Lys-Arg-Asn-Lys-Asn-Ile-Ala-COOH and possibly modified in the N-terminal region. A specific action of bioactive enteroglucagon, increase in cAMP, has been found in the acid-secreting fundic part of the rat stomach. The term "oxyntomodulin" is therefore proposed to describe this peptide.

Neuropeptides in the gut: quantification and characterization of cholecystokinin octapeptide-, bombesin- and vasoactive intestinal polypeptide-like immunoreactivities in the myenteric plexus of the guinea-pig small institute

The localization of CCK8-, bombesin- and VIP-like immunoreactivities in the myenteric plexus of the guinea pig small intestine has been studied by radioimmunoassay of extracts of longitudinal muscle strips obtained with and without adherent myenteric plexus; concentrations were compared with those in other regions of the gut. In innervated strips of longitudinal muscle of ileum there was approximately 14 pmol/g CCK8-, 32 pmol/g bombesin- and 135 pmol/g VIP-like immunoreactivity; concentrations were reduced by over 70% in denervated strips. Gel filtration and ion exchange chromatography indicated that over 80% of CCK immunoreactivity was due to CCK8; no evidence was found of significant amounts of smaller COOH-terminal fragments. Bombesin immunoreactivity occurred in two forms, the major one resembling the amphibian tetradecapeptide in its elution from gel filtration columns. Immunoreactive VIP differed markedly from porcine VIP in immunochemical and chromatographic properties; the data suggest that guinea pig VIP is less basic than porcine VIP and that the two peptides differ in structure in their NH2-terminal regions. Some functional implications of these findings are discussed.

A derivative of R-type cyanocobalamin binding proteins in the human intestine. A candidate antibacterial molecule

Human jejunal fluid contains a protein which has a molecular radius of 3.37 nm, an Mr or 60600 and a mean pI of 3.35 and binds cobalamin with a K of 0.1 . 10(9) l/mol. This protein also couples cobalamin analogues lacking the nucleotide moiety, cross-reacts with R-type protein and is resistant to proteolysis in the intestine. These findings refute the hypothesis that cobalamin-analogue binders are present and effectively inhibit the bacterial uptake of analogues in the intestine.