Hydrocarbons in digestive tract and liver of a basking shark.

The hydrocarbons of zooplankton pass through the digestive tract of the basking shark without fractionation or structural modification. They are resorbed in the spiral valve and deposited in the liver. In contrast to unsaturated fatty acids, the olefinic hydrocarbons are not decreased in concentration. The hydrocarbon assemblage in the digestive tract and in the liver is indicative of the food sources and feeding grounds of the shark. Squalene, abundant in shark liver, occurs only in traces in zooplankton; phytane, if present at all, constitutes less than 0.005 percent of the hydrocarbons of zooplankton and of shark liver.

Measurement, characterization, and source of somatostatin-like immunoreactivity in human amniotic fluid.

Somatostatin-like immunoreactivity (SLI) is widely distributed in tissues and biological fluids. To determine whether SLI is also present in amniotic fluid, samples obtained by amniocentesis from 30 normal and 27 abnormal pregnancies were studied by radioimmunoassay. Direct incubation of [(125)I-Tyr(1)]tetradecapeptide somatostatin (SRIF) with amniotic fluid resulted in 89% tracer degradation. Damage was reduced to <5% when samples were acidified and boiled before the assay. With this technique, SLI was detectable in all normal amniotic fluid samples; the mean level at 15-20 wk of gestation (320+/-55 pg/ml, n = 15) being 4.5 times higher than the mean at 32-43 wk (70+/-12 pg/ml, n = 15) (P < 0.001). In cases of preeclampsia (n = 6), gestational diabetes (n = 5), anencephaly (n = 1), and meningomyelocele (n = 1), SLI values were in the normal range, but in one juvenile diabetic and one patient with chronic renal failure, SLI was undetectable (<10 pg/ml). In a pair of monochorionic diamniotic twins, SLI levels were very different (33 and 197 pg/ml), which suggests that fetal factors are more important than materno-placental ones in determining amniotic fluid SLI. Serial dilutions of amniotic fluid showed parallelism with standard SRIF. When concentrates of pooled amniotic fluid were chromatographed on Sephadex G-25 columns, all SLI eluted in the void volume ahead of SRIF even after treatment with 8 M urea and dithiothreitol. This "big" SLI incubated in amniotic fluid showed 100% stability over 24 h at 37 degrees C, whereas SRIF was rapidly inactivated (t((1/2)) congruent with 7 min). Extracts of placenta and fetal membranes contained no SLI, but small amounts (6-20% of total amniotic fluid SLI) were found in cells from fresh fluid. Radioimmunoassay of SLI in extracts of seven paired cord arterial and venous plasma samples showed no arteriovenous gradient consistent with fetal origin of cord blood SLI. It is concluded that (a) amniotic fluid contains SLI which is of fetal origin and (b) normal levels vary with gestational age. The SLI has a higher molecular weight (>/=5,000) and is more stable in amniotic fluid than SRIF.

Immunoreactive apolipoprotein E is a widely distributed cellular protein. Immunohistochemical localization of apolipoprotein E in baboon tissues.

Apolipoprotein (apo)E is an important protein determinant in cholesterol homeostasis in man. The protein is synthesized by the liver as well as by a number of extrahepatic tissues. In the present study, immunohistochemical techniques were used to identify apoE in specific cells in various baboon organs. In the 11 tissues studied, the following cell types have been found to harbor apoE immunoreactivity: cerebral astrocytes; thyroid follicular cells; alveolar type II pneumocytes; hepatocytes, and Kupffer cells; adrenocortical cells in zona fasciculata and zona reticularis; adrenal medullary cells; some renal tubular epithelia; some pancreatic islet cells; histiocytic macrophages in lymph nodes and the spleen; some gastric mucosal epithelia; and ovarian oocytes. These observations indicate the wide distribution of apoE in many organs and suggest that the protein might perform other important functions such as regulation of local hormonal homeostasis in addition to its role in cholesterol metabolism.

Distribution of marker enzymes and mucin in intestinal metaplasia in human stomach and relation to complete and incomplete types of intestinal metaplasia to minute gastric carcinomas.

Intestinal metaplasia of the human stomach was classified into two types, complete and incomplete. The complete type was associated with the intestinal marker enzymes sucrose alpha-D-glucohydrolase, alpha, alpha-trehalase, aminopeptidase (microsomal) (APM), and alkaline phosphatase (ALP). Tissue of this type contained goblet cells and Paneth's cells but not high-iron diamine (HID)-positive mucin staining with HID-Alcian blue. The incomplete type of intestinal metaplasia was associated with sucrose alpha-D-glucohydrolase, APM, goblet cells, and HID-positive mucin but not with alpha, alpha-trehalase, ALP, or Paneth's cells. For the examination of the distribution of the complete and incomplete types in 84, 27, and 16 resected specimens of human stomach with gastric carcinoma, gastric ulcer, and duodenal ulcer, respectively, disaccharidases were located with Tes-Tape. Specimens with intestinal metaplasia were divided into three classes: complete type only (class I), incomplete type only (class II), and a mixture of areas of the complete and incomplete types (class III). Of the 84 specimens from patients with gastric carcinoma, intestinal metaplasia was found in 76 (01%), and the percentages of specimens of classes I, II, and III were 32, 22, and 46, respectively. In these specimens, the percent incidence of class I increased and that of class II decreased with age. Of the 27 specimens from patients with gastric ulcer, 16 (59%) shopwed intestinal metaplasia and 10 of the 16 (63%) specimens were of class II. Of the 16 specimens from patients with duodenal ulcer, only 3 (19%) specimens showed intestinal metaplasia and all of them were of class II. The relationships of the complete and incomplete types of intestinal metaplasia to gastric carcinoma wre studied in 26 foci of minute carcinoma of the stomach less than 5 mm in largest diameter. Nineteen of 20 (05%) foci of the intestinal type of minute carcinoma were surrounded by intestinal metaplasia and 16 foci (80%) were surrounded by the incomplete type of intestinal metaplasia.

Toxic chemicals in marine sediment and biota from Mukilteo, Washington: relationships with hepatic neoplasms and other hepatic lesions in English sole (Parophrys vetulus).

High prevalences of idiopathic liver lesions, including 7.5% hepatic neoplasms (e.g., hepatocellular and cholangiocellular carcinomas) and 16.7% foci of cellular alteration (putative preneoplastic hepatic lesions), were found in English sole (Parophrys vetulus) from waters near Mukilteo, a small community on Puget Sound in Washington State. Sediments from the sampling sites contained particularly high concentrations of aromatic hydrocarbons. Substantially lower concentrations of these compounds were found in sediments from another Puget Sound (reference) site in which fish showed no evidence of hepatic neoplasms or foci of cellular alteration. Stomach contents from the fish at Mukilteo contained substantially higher concentrations of the chemicals than did stomach contents of fish from the relatively uncontaminated site. High concentrations of metabolites of aromatic compounds were measured in the bile of fish from Mukilteo. These findings support previously observed relationships between sediment chemicals (e.g., aromatic hydrocarbons) and high prevalences of liver lesions in English sole from Puget Sound. In addition, a dietary route of uptake by English sole of environmental chemicals, including known carcinogens, was documented.

Metabolism of benzo[a]pyrene on the nasal mucosa of Syrian hamsters: comparison to metabolism by other extrahepatic tissues and possible role of nasally produced metabolites in carcinogenesis.

The formation of metabolites of nasally instilled benzo[a]pyrene [(BP) CAS: 50-32-8] was determined. The study was prompted by a report that a high incidence of tumors occurred in tissues of the upper respiratory and alimentary tracts of Syrian hamsters exposed to BP aerosols. The esophagi of anesthetized hamsters were surgically catheterized so that radiolabeled material instilled as BP in the nose could be collected and analyzed for metabolites. About 50% of the instilled BP was metabolized in the nose and, potentially, would have been swallowed in an awake animal. In auxiliary experiments, homogenates of respiratory and alimentary tissues were tested for metabolic activity for BP. The nose, trachea, and lungs had about equally high activities on a per organ basis (5-7 nmol/hr), whereas all other tissues had considerably less activity. The results of the study indicate that nasal metabolism may be important in causing tumors in alimentary as well as upper respiratory tissues.

Enhancement of glutathione S-transferase activity of the mouse forestomach by inhibitors of Benzo[a]pyrene-induced neoplasia of the forestomach.

The effects of glutathione S-transferases (GST) activity and acid-soluble sulfhydryl levels of a number of compounds previously investigated for their capacity to inhibit benzo[a]pyrene (BP)-induced neoplasia of the mouse forestomach were determined. Five of the compounds studied increased the GST activity of the forestomach 78-182%. The five compounds were: p-methoxyphenol, 2-tert-butyl-4-hydroxyanisole, coumarin, alpha-angelicalactone, and benzyl isothiocyanate. With the exception of benzyl isothiocyanate. With the exception of benzyl isothiocyanate, these compounds also increased acid-soluble sulfhydryl levels, but to a lesser magnitude. All five chemicals inhibited BP-induced neoplasia of the forestomach. These data indicate that enhancement of the GST activity by an amount of about 75% or greater is associated with a reduced carcinogenic response of the forestomach to BP. The data also suggest that such enhancement might be used as a method of identifying compounds likely to inhibit BP and other carcinogens detoxified in a similar manner. Inasmuch as inhibition of the action of carcinogens may involve mechanisms other than detoxification by GST, the failure to increase GST activity substantially does not rule out the possibility of a compound being an inhibitor.

Immunological characterization and clinical implication of cobalamin binding protein in human gastric cancer.

Cobalamin (vitamin B12) binding protein was purified from gastric cancer extracts and from serum-free culture medium of cancer cell line KATOH-III. The molecular weight, determined by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 70,000 and the pI was 2.8 to 3.2. From biochemical and immunological properties, this cobalamin binding protein was considered to be an isoprotein of cobalamin R binder. Monoclonal antibodies were produced against saliva R and cobalamin binding protein in culture medium to study their antigenic determinants. Monoclonal antibody 55-D reacted to an epitope of peptide in both binders, whereas WK-1 and H-12 reacted to determinants of a carbohydrate moiety, including sialic acid, in cancer cell-derived binder. In addition, we carried out an enzyme-linked immunoassay and examined plasma levels of immunoreactive R binder in patients with gastric cancer (n = 72), benign gastrointestinal disease (n = 30), and healthy individuals (n = 40). Even in patients without liver metastasis, the level of immunoreactive R binder detected by monoclonal antibody H-12 was elevated in some patients and decreased after excision of the tumor. R binder was also elevated in cancer tissue extract. Immunoreactive binder was histochemically detected in the cytosol of cancer cells and metaplastic cells of the gastric mucosa. The present findings suggest that cobalamin R binder is de novo synthesized in gastric cancer cells and that its plasma level increases in some patients. This binding protein may be a useful diagnostic and therapeutic parameter.

Nuclear magnetic resonance investigations of human neoplastic and abnormal nonneoplastic tissues.

A large number of samples of human neoplastic and abnormal nonneoplastic tissues were studied by nuclear magnetic resonance spectrometry in order to evaluate the possible role of this technique in the diagnosis of cancer. The spin-lattice magnetic relaxation times (T1) of abnormal nonneoplastic tissue were longer, in many instances, than those of malignant tumors from similar sites, preventing recognition of the tumors in this manner. The evidence for the nonspecific nature of the prolongation of T1 in abnormal tissue is reviewed, and additional limitations of this technique in the diagnosis of cancer are indicated.

Characterisation of N-terminally extended met-enkephalin Arg6Gly7Leu8 variants in the porcine upper digestive tract.

Proenkephalin A-derived peptides are known to occur in the gut, but their precise identity is uncertain. We report here the isolation of N-terminally extended forms of Met-enkephalin Arg6Gly7Leu8 from porcine upper digestive tract monitored by radioimmunoassay. A single major form was identified in pyloric antral muscle and mucosa, but in the duodenum two major forms were detected. Microsequence analysis together with immunological data revealed that the antral mucosal peptide and the most acidic duodenal peptide had identical amino-acid sequences, corresponding to a 5.3 kDa peptide terminating in Met-enkephalin Arg6Gly7Leu8. The data indicate that high-molecular-weight peptides may constitute a major proportion of gut opioid peptide immunoactivity.

Gangliosides of the human gastrointestinal mucosa.

Gangliosides of the human alimentary mucosa were purified and analysed with thin-layer chromatography and gas chromatography. The content of ganglioside neuraminic acid was 0.16 mumol/g dry weight in the stomach, 0.07 mumol/g dry weight in the small intestine and 0.11 mumol/g dry weight in the large intestine. Mono- and disialosylhemosides were the major gangliosides, on a molar basis 68% of the total found in the stomach and 44% of the total in the small and large intestine. Considerable amounts of more complex gangliosides were found, especially in the small and large intestine, in which the molar content of tri- and tetraglycosylgangliosides containing galactosamine made up 38% of the total. Two glucosamine-containing gangliosides were also found, the probable structures of which were mono- and disialotetraglycosylceramide. The presence of the latter is reported for the first time.

Temporal relationship of tissue somatostatin-like immunoreactivity to metabolic changes in genetically obese and diabetic mice.

Somatostatin-like immunoreactivity (SRIF-LI) content in 2 N acetic acid extracts of hypothalamus, gastric antrum, and pancreas was measured in genetically obese (C57BL/6J ob/ob and db/db) and diabetic (C57BL/KsJ db/db and ob/ob) mice and normal littermate controls from 5 to 24 wk to determine the relationship of previously reported changes to the development of metabolic abnormalities. Hypothalamic SRIF-L concentration was similar in control, diabetic, and obese mice at all ages and increased progressively with age in all groups. Gastric antrum SRIF-LI was similar in all groups of mice at all ages. Obese mice gained weight progressively and showed moderate hyperglycemia and marked hyperinsulinemia from 5 wk of age. Pancreatic SRIF-LI content in obese (C57BL/6J) animals was similar to that in lean littermate controls, but pancreatic SRIF-LI concentration (expressed by weight or protein content) was decreased until 8 (6J ob/ob) and 10 (6J db/db) wk. Diabetic (C57BL/KsJ) mice showed a similar metabolic pattern until 10 wk with no change in pancreatic SRIF-LI content or concentration. Thereafter a progressive fall in serum insulin and a marked rise in serum glucose was associated with increasing pancreatic SRIF-LI content and concentration. These studies suggest that the genetically hyperphagic syndromes are unassociated with any change in hypothalamic or gastric SRIF-LI; that pancreatic SRIF-LI increases occur in response to, rather than as the cause of, relative hypoinsulinemia; and that the genetic background of the mice (KsJ or 6J) rather than the mutant gene (db or ob) determines the defect in carbohydrate metabolism and the pancreatic SRIF-LI response.

Developmental regulation of somatostatin gene expression in the brain is region specific.

Developmental regulation of somatostatin (SRIF) gene expression was studied in five regions of rat brain and in rat stomach. Total RNA was isolated from hypothalamus, cortex, brainstem, cerebellum, and olfactory bulb, as well as stomach at eight stages of development from prenatal day 16 to postnatal day 82. Hybridization of a 32P-labeled rat SRIF cDNA probe to Northern blots of total RNA from the above tissues during development demonstrated a single hybridizing band approximately 670 base pairs in length. When SRIF mRNA levels from each stage of development were quantified and normalized by the amount of poly (A)+ RNA present at that stage of development, a unique pattern of SRIF gene expression was seen in each region. In brainstem and cerebellum, SRIF mRNA levels peaked early in development between prenatal day 21 and postnatal day 8 and then declined until postnatal day 82. Hypothalamus and cortex, on the other hand, showed a progressive increase during development with peak levels occurring between postnatal days 13 and 82. In contrast, stomach and olfactory bulb showed SRIF mRNA levels which were low during early development and which rose late in development (postnatal days 13 to 82). Marked differences in the amount of SRIF mRNA within each region were present as well. These data suggest that there is differential expression of the SRIF gene in different regions of the brain and in the stomach during development. Further study of this phenomenon may provide insight into the in vivo control of SRIF gene expression and the role of SRIF in the developing brain.

A comparative analysis of intermediate filament proteins in bovine heart Purkinje fibres and gastric smooth muscle.

The intermediate filament (IF) composition of muscle cells of various sources is still a controversial issue. In the present study, the IF composition of bovine Purkinje fibres (PFs), atrial and ventricular myocardium, and gastric smooth muscle (SM) has been compared using biochemical and immunocytochemical methods. The Mr of the major IF subunit protein in all four tissues was 55,000. In two-dimensional (2-D) electrophoresis gels of Triton-treated ordinary atrial and ventricular myocardium and the gastric muscular wall, two or three isoelectric isoforms were seen, whereas in PFs up to seven isoforms caused by phosphorylation were observed. In immunofluorescence studies antibodies against the Mr 55,000 subunit of PFs and gastric SM, respectively, both showed identical reactivity with PFs, atrial and ventricular myocytes, gastric SM cells and some SM cells in intramyocardial and gastric muscular wall blood vessels. A small amount of vimentin (Mr 57,000) was also detected in 2-D gel electrophoresis in all four tissues as well as in immunoblotting of PFs with antibodies to vimentin. Immunofluorescence studies using both polyclonal and monoclonal antibodies to vimentin showed that vimentin was present in the endothelium and SM cells of both intramyocardial and gastric muscular wall vessels, sometimes together with desmin in the vascular SM cells, but was never seen in PF, atrial, ventricular or gastric SM cells proper. As expected, vimentin was present in interstitial tissue, i.e., fibroblasts and capillaries. However, interestingly, the monoclonal antibodies, which recognized different antigenic determinants of vimentin, did not give identical staining patterns. Especially the staining of the vascular SM cells differed. Since this staining pattern did not change upon denaturation and unmasking experiments, it seems that the organization of vimentin in different mesenchymal cell types varies. Vimentin was also detected in isolated PFs but here it was located solely in the contaminating interstitial tissue. Thus, desmin is the sole IF protein expressed in PFs, in atrial and ventricular myocytes and in gastric SM cells proper; vimentin alone being present in the interstitial tissue cells, whilst in vascular SM cells desmin and vimentin are coexpressed in various proportions. The variation in number of isoforms of desmin and the heterogeneity in staining of mesenchymal tissues with monoclonal vimentin antibodies probably indicates that the IF cytoskeletons are differently organized in various cell types, even though they contain IFs of the same class.

Beta-endorphin and adrenocorticotropin in extrapituitary sites: gastrointestinal tract.

Beta-Endorphin and ACTH immunoassays were employed to examine the concentrations, distributions, and character of those peptides in rat gastrointestinal tissues. Sections of the gastrointestinal tract were obtained from fasted and fed animals and were extracted in 5 N acetic acid containing proteolytic enzyme inhibitors. Aliquots immunoassayed for beta-enddorphin and ACTH revealed highest concentrations to be present in the small bowel, with stomach and colon containing little immunoreactivity. Tissues from fasted animals contained more immunoreactivity than did those from fed animals. Gel chromatography showed the presence of large molecular weight forms of beta-endorphin and ACTH in gut extracts. Concanavalin A affinity chromatography revealed that approximately 5% of gut immunoreactivity contained carbohydrate. Therefore, beta-enddorphin and ACTH immunoreactivities are present im the gut. The demonstration of large molecular weight and glycosylated forms of immunoreactivity suggests the presence of biosynthetic precursors of beta-endorphin and ACTH. The increase in immunoreactivity in response to fasting suggests that these peptides play a role in gut physiology.

Phylogenetic and anatomical distribution of somatostatin in vertebrates.

Immunoreactive GH release-inhibiting factor [somatostatin (SRIF)] was detected in hypothalamus, extrahypothalamic brain, pancreas, and stomach extracts of the rat, pigeon, tortoise, frog, teleost (cichlid), and elasmobranch (dogfish) and in the whole brain of the cyclostome (hagfish). The SRIF concentration was higher in the pancreas and gastrointestinal tract than in the hypothalamus and extrahypothalamic brain in most species. Extracts of the various tissues from the different species assayed in serial dilutions gave displacement curves parallel to those of synthetic mammalian SRIF. Cation exchange chromatography of hypothalamic extracts from the various species revealed two major immunoreactive peaks, one of which correpsonds to synthetic SRIF in elution volume, the other being less basic. Affinity chromatography-purified immunoreactive SRIF from frog brain, pancreas, and stomach extracts coeluted with synthetic SRIF in high pressure liquid chromatography. The results indicate that immunoreactive SRIF in various tissues and in different vertebrates is indistinguishable and suggest that there has been no change in the molecule during at least 400 million yr of evolution.

Properties of somatostatin-like immunoreactive polypeptides in the canine extrahypothalamic brain and stomach.

Polypeptides with somatostatin-like immunoreactivity (SLI) and approximate molecular weights of 12,000, 3,000, and 1,600 were isolated from acid extracts of the canine extrahypothalamic brain and stomach by affinity chromatography, ion exchange, gel filtration, and isoelectric focusing. The 12,000-dalton SLI was acidic, whereas the 3,000- and 1,600-dalton forms were basic molecules. All SLI fractions diluted proportionally in a RIA employing an antibody directed toward the central region of somatostatin. Like synthetic somatostatin, the 1,600-dalton SLI inhibited pentagastrin-stimulated gastric acid secretion in rats. Neither of the two larger forms of SLI were dissociated by 6 M guanidinium HCl. However, treatment with dithiothreitol, which reduces disulfide bonds, resulted in the conversion of a large portion of the 12,000-dalton SLI to the 1,600-dalton form. These data are compatible with a model of a 12,000-dalton SLI consisting of somatostatin bound to an acidic polypeptide by a peptide bond and a disulfide bond. Variations in the relative rates of hydrolysis of the peptide bonds and reduction of the disulfide bonds in different tissues may result in three forms of the 12,000-dalton polypeptide in which both bonds are intact or one of the two bonds is cleaved.

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.

The use of radioimmunoassay to compare the tissue and subcellular distributions of neurotensin and neuromedin N in the cat.

A RIA for neuromedin N (NMN) was developed using 125I-labeled NMN and rabbit antisera raised against a synthetic NMN coupled to NH2-enriched putrescine-thyroglobulin. One of the antisera (TG-B), which cross-reacted less than 3% with the related substances, neurotensin (NT), Lys8,Asn9-NT8-13, and xenopsin, was used to compare the distribution of immunoreactive NMN (iNMN) in the cat to that of immunoreactive NT (iNT). Although both iNMN and iNT were found primarily in the mucosa of the ileum, brain, pituitary, and adrenal, the ratio of the two activities varied, depending upon the tissue. Feline iNMN from brain, intestine, and adrenal was indistinguishable from synthetic NMN by HPLC. In contrast, extracts of stomach and pancreas contained primarily NMN-related cross-reacting substances, the concentrations of which increased up to 500-fold within minutes of extraction in aqueous acid. Since these peptides were also present to some extent in acid/acetone extracts, they appear to be endogenous variants of NMN stored in precursor forms which could be activated by acid-proteases. During sucrose gradient centrifugation of isotonic homogenates of feline brain, intestine, and adrenal, iNMN and iNT comigrated in association with synaptosome-like and vesicle-like particles, as identified by electron microscopy. These results demonstrate the presence of a peptide similar to porcine NMN in extracts of feline brain, adrenal, and small intestine and its association with signaling vesicles. In addition, the ability of gastric and pancreatic extracts to generate variants of NMN in large quantity is described.

Distribution of oxyntomodulin and glucagon in the gastrointestinal tract and the plasma of the rat.

Oxyntomodulin (OXM), an intestinal glucagon-containing peptide extended at its C-terminal end by an octa-peptide, is one of the gut glucagon-like immunoreactants (GLI) or enteroglucagon. The distribution of OXM and glucagon was determined in the gastrointestinal tract and in the plasma of the rat. Reversed-phase HPLC, associated with RRA or RIA, performed with an N-terminally directed glucagon antiserum (GOL), was used. HPLC of intestinal extracts or plasma separated the GOL immunoreactivity into three peaks: two major peaks coeluting with a preparation of rat glicentin (peak I, partially purified from rat intestine) and porcine or rat OXM, respectively, and a smaller peak coeluting with glucagon. The behavior of the three peaks in the analytical systems matched that of glicentin, OXM, and glucagon, respectively, allowing their identification. The concentrations of OXM picomoles per g of tissue) gradually increased from the duodenum (9 +/- 1) to ileum (93 +/- 4), thereafter decreasing in cecum and colon (22 +/- 3). In the gut, OXM, glucagon, and peak I averaged 40%, 1%, and 59% of the total GLI, respectively. OXM was present in significant amounts in the pancreas (18% of GLI) and stomach (27% of GLI), two tissues in which it accounted, together with glucagon, for almost the totality of GLI. In 24 h-fasted rats, plasma concentrations of OXM, glucagon, and peak I, determined after HPLC with GOL antiserum, were 15.1 pM, 8.6 pM, and 12.3 pM, respectively. Two hours after refeeding, both OXM and peak I were significantly increased (P less than 0.05 and P less than 0.02) by a similar factor (2-fold), while glucagon remained unchanged. When the HPLC results were compared with RIA measurement of GLI (GOL antiserum) and glucagon (with a C-terminal glucagon antiserum) in plasma, enteroglucagon (GOL--C-terminal glucagon antiserum immunoreactivities) correlated well with the sum of OXM plus peak I. The combination of HPLC and RRA or RIA allows the unambiguous determination of OXM, glucagon, and glicentin (peak I) in tissues and plasma. In the rat intestine and in the plasma, OXM and glicentin appear roughly in the same ratio and seem to be the major components, if not the totality, of enteroglucagon.