Identification of bombesin receptors on isolated muscle cells from human intestine

Smooth muscle cells were isolated separately from the longitudinal and circular muscle layers of human jejunum obtained at surgery and used to determine whether amphibian bombesin-14 and 3 mammalian homologues, GRP-(1-27), GRP-(18-27) and neuromedin B, can cause contraction by acting directly on muscle cells. Circular and longitudinal muscle cells contracted identically in response to bombesin-14 (C50 2 x 10(-12) M). The contractile response was not affected by selective muscarinic, opioid, CCK or serotonin antagonists but was inhibited by the substance P (SP) derivative, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]SP. All 3 mammalian bombesins were less potent than bombesin-14. GRP-(1-27) and GRP-(18-27) were equipotent (C50 4 x 10(-11) M) but 20 times less potent than bombesin-14. Neuromedin B (C50 6 x 10(-12) M) was 3 times less potent than bombesin-14. All bombesins, however, were more potent than other enteric neuropeptides (e.g., tachykinins, opioid peptides). The study demonstrates conclusively the ability of bombesins to cause direct contraction of intestinal smooth muscle cells.

Lectin binding sites in duodeno-jejunal mucosae from coeliac children

The distribution pattern of some labelled lectins (WGA, SBA, PNA, DBA, ConA, LCA) has been investigated in small intestinal mucosa of coeliac children (119 cases) and normal (short stature) and pathological (postenteritis syndrome) controls. The oligosaccharide side chains of glycoproteins present in the cytoplasm and in the brush border of enterocytes, goblet cells and luminal crypt surface have been revealed. The most important differences in lectin binding reactivity between coeliac and controls mucosae are discussed.

Lectin histochemistry of goblet cells in metaplastic epithelium of human gallbladder

Goblet cells arising in the intestinal metaplasia of chronically inflamed gallbladder were studied by lectin histochemistry and compared with equivalent cells in the small and large intestine. Overall, metaplastic goblet cells reacted more avidly with the majority of lectins and even expressed receptors for lectins that were unreactive with normal intestinal goblet cells. There was, however, considerable variation in lectin binding from one case to another, as well as among the cells of the same specimen. We thus conclude that metaplastic goblet cells in the gallbladder are different from normal intestinal goblet cells, but do not have a uniform lectin binding profile.

On the origin of intestinal transferrin

The incorporation of 35S-L-methionine (35S-Met) into TCA-precipitable protein is used to measure protein synthesis in isolated non-vascular perfused jejunal segments and in isolated liver cells under steady-state conditions in rats. 10(5) X g supernatants of homogenates from jejunal segments and from liver cells as well as the jejunal absorbate were processed immuno-electrophoretically. Incorporation of 35S-Met radioactivity into precipitin lines with sera against transferrin, IgG and plasma proteins were autoradiographed and compared semiquantitatively with each other. Calculated on a wet-weight basis this system is sensitive enough to detect transferrin synthesis down to a level of 1% of that in the liver. Still, no transferrin synthesis was found in the jejunal mucosa, while 35S-Met incorporation into TCA precipitates and into IgG continued in isolated jejunal segments for over 2 h. A good correlation was found (r = 0.88, P less than 0.01) between mucosal and plasma transferrin in normal as well as in iron deficient rats. A complete immunologic cross-reactivity could be demonstrated between different plasma transferrins and the transferrin in three different preparations of the intestinal mucosa. Immunoblots of electropherograms after isoelectric focussing showed no distinct differences between transferrin in the plasma, bile, and in the mucosal epithelium.

Autoradiographic distribution of vasoactive intestinal polypeptide receptors in rabbit and rat small intestine

Vasoactive intestinal peptide (VIP) is found in the enteric nervous system of all layers of the small intestine. In the gastrointestinal tract, VIP receptors coupled to adenylate cyclase are present on epithelial, smooth muscle and possibly mononuclear cells. This study analyzes the distribution of VIP binding using in vitro autoradiographic techniques. VIP binding was present in high density in the mucosal layer of rabbit duodenum, jejunum and ileum. Low VIP binding was noted over the smooth muscle layers or the lymphoid follicles. Similar results were obtained in rat small intestine. The density of VIP binding was greatest in duodenal mucosa but was present in lower density in jejunal and ileal mucosa. Again, low VIP binding was noted in the smooth muscle layers or lymphoid follicles. Thus, autoradiographic maps of small intestine indicate that VIP receptors are found primarily in the small intestinal mucosa.

Histochemical changes in the composition of mucins in goblet cells during methotrexate-induced mucosal atrophy in rats

Changes in the composition of mucins in jejunal goblet cells were investigated histochemically after a single intraperitoneal injection of methotrexate in rats (40 mg methotrexate/kg body weight). At 48 h after injection of methotrexate, when mitotic activity in the crypts approximates to zero, an almost complete disappearance of mucin-containing goblet cells can be observed. At 96h, when proliferative activity in crypts is excessive, neutral mucin- and sialomucin-containing goblet cells dominate in the crypts, whereas in controls the crypts display sulphomucin-containing goblet cells. At 144h neutral mucin- and sulphomucin-containing goblet cells dominate in the crypts. Both at 48 and 96h after injection of methotrexate a significant decrease in the number of villous goblet cells takes place, whereas with respect to the quality of the mucins in the goblet cells no difference can be found in comparison with control rats. At 144h the villi have recovered from the preceding temporary decrease of goblet cells. The histochemical composition of the population of goblet cells is still aberrant and shows goblet cells containing neutral mucins and sulphomucins principally, whereas in controls sialomucin-containing goblet cells dominate on the villi. The established changes in the composition of mucins in goblet cells cannot be attributed to methotrexate-induced malnutrition, as pair-fed control rats clearly demonstrate. Our results clearly demonstrate that conspicuous quantitative as well as qualitative changes in the synthesis of mucins in goblet cells occur during the hyporegenerative and hyperregenerative phase of methotrexate-induced mucosal atrophy.

Effects of treatment with smectite on gastric and intestinal glycoproteins in the rat: a histochemical study

A histochemical study was carried out to evaluate the changes that occur in the glycoproteins of the rat digestive tract following short term treatment with a clay smectite. Staining with the usual methods for detecting complex carbohydrates and with lectin conjugates (Con A, LTA, PNA, SBA and WGA) showed that the stomach was the susceptible organ. Increased staining with LTA and SBA, together with a decrease in the abundance of sulphate groups in the upper mucous neck cells, was observed after the clay treatment. Such treatment induced only slight changes in jejunal and colonic glycoproteins while no modification was observed in the colon. These data suggest that the content of mucus-producing cells could be affected by smectite, even following short-term treatment.

Isolation and partial characterization of plasma membrane fatty acid binding proteins from myocardium and adipose tissue and their relationship to analogous proteins in liver and gut

We describe a general method for isolating a class of 40 kDa plasma membrane fatty acid binding proteins which have been identified previously only in rat liver and jejunum. Proteins extracted with 2 M salt from rat adipocyte and cardiac myocyte plasma membranes were subjected to preparative isoelectric focusing. Fractions with pI's greater than or equal to 9.0 were further purified by oleate-agarose affinity chromatography and HPLC. Each tissue yielded a single 40 kDa protein which co-chromatographed with [3H]-oleate on gel permeation HPLC, and reacted on Western blots with an antibody to the corresponding hepatic membrane protein. Related plasma membrane fatty acid binding proteins have now been isolated from each of the major sites of fatty acid transport.

Localization in the gastrointestinal tract of immunoreactive prosomatostatin

Antisera against 5 different regions of the entire prosomatostatin molecule were used for immunohistochemical mapping of prosomatostatin-containing structures in the pig gastrointestinal tract, and for radioimmunological and chromatographical analysis of the products of prosomatostatin in extracts of ileal mucosa. The latter showed that the antisera were capable of identifying components containing N-terminal as well as C-terminal parts of prosomatostatin. Endocrine cells were identified with all antisera in most parts of the gastrointestinal tract, and varicose nerve fibres were observed in all parts of the small intestine but not in the stomach and the colon. The colon contained very few immunoreactive structures. Immunoreactive nerve cell bodies were found in the submucous plexus of the small intestine. All immunoreactive endocrine cells in the stomach and the duodenum and all immunoreactive nerves were stained by all 5 antisera whereas the small intestinal endocrine cells did not stain for the most N-terminal region of prosomatostatin. The results suggest that all gastrointestinal somatostatin is derived from the same precursor molecule, which, however, in the small intestinal endocrine cells is processed differently from that of the other tissues.

Intestinal apoB synthesis, lipids, and lipoproteins in chylomicron retention disease

Chylomicron retention disease is characterized by fat malabsorption, hypocholesterolemia, normal fasting triglycerides, and marked intestinal steatosis despite the presence of both plasma and intestinal apoprotein B. The defect remains unknown but presumably involves the synthesis or secretion of chylomicrons. The present investigation examines this hypothesis by studying the biosynthesis of chylomicrons in cultured jejunal explants and by defining the quantitative and qualitative abnormalities of plasma lipids and of circulating lipoproteins. Following 2-3 years of a low fat diet supplemented with medium chain triglycerides, six patients with chylomicron retention disease had significantly higher triglyceride (TG) levels coupled with a decrease in both free (FC) and esterified cholesterol (EC) as well as in essential fatty acids and phospholipids (PL) when compared to healthy controls. The low total plasma cholesterol was largely accounted for by low levels of both low density (LDL) and high density lipoprotein (HDL) cholesterol. VLDL and LDL were characterized by a diminished percentage of CE with an increase of TG while HDL contained relatively more FC as well as PL and less CE. The diameter of VLDL was larger whereas those of LDL and HDL were smaller than in normal controls. Jejunal explants, when incubated with [14C]palmitate, were capable of normal biosynthesis of TG, diglycerides, PL, and CE. These lipids, however, except for PL, were retained in the tissue and could not be secreted into the culture medium. Incubation of intestinal biopsies with [3H]leucine and [14C]mannose resulted in normal protein synthesis and reduced glycosylation. The presence of intestinal apoB-48 was confirmed by immunoblot using 2D8 antibodies. These data suggest that the intestinal defect in this disease results from a disorder of the final assembly of chylomicrons or in the mechanism of their exocytosis.

Cellular retinol-binding protein (type two) is abundant in human small intestine

Human small intestine was found to contain a retinol-binding protein similar to the gut-specific cellular retinol-binding protein, type two [CRBP (II)], described in the rat. This newly detected human protein was immunochemically distinct from human cellular retinol binding protein previously described but immunochemically similar to rat CRBP (II). The partially purified protein bound retinol and exhibited fluorescence excitation and emission spectra distinct from those spectra for retinol bound to pure human CRBP but similar to the spectra for retinol bound to rat CRBP (II). Human CRBP (II) could be localized to the villus-associated enterocytes by immunohistochemistry, using antiserum against rat CRBP (II). The protein was abundant representing 0.4% of the total soluble protein in a jejunum mucosal extract. This protein may play an important role in the absorption and necessary intestinal metabolism of vitamin A.

Flameless atomic absorption spectrophotometric determination of platinum in tissues solubilized in hyamine hydroxide

Processing biological samples by solubilization in Hyamine hydroxide (methylbenzethonium hydroxide) as an alternative to wet ashing with concentrated nitric acid for atomic absorption determination of platinum has been explored. The concentrations of platinum in tissues removed from rats 2 h after they had received the antitumor drug Carboplatin (60 mg/kg, iv) were comparable using either of the procedures, indicating the utility of tissue solubilization. Limits of detection were also comparable between the Hyamine hydroxide (0.25 microgram platinum/g) and nitric acid (0.15 microgram/g) procedures. The solubilization method, however, has advantages over wet digestion because of its simplicity and greater safety.

Bile acid concentrations in serum, bile, jejunal contents, and excreta of male broiler chicks during the first six weeks posthatch

Bile acid concentrations in serum, bile, jejunal contents, and excreta of male broiler chicks during the first six weeks posthatch were determined. Bile acid concentrations in serum, jejunum, and excreta declined significantly (P less than .05) during the 1st week after hatch. Serum and jejunal concentrations then rose through week 3, declined during Weeks 4 and 5, and by 6 weeks of age had returned to levels comparable to those seen at Week 3. After the 1st week, no further significant changes were seen in bile acid concentrations in excreta. Concentrations of bile acids in bile were significantly higher at Weeks 1, 3, 5, and 6 than at Weeks 2 and 4. Predictive polynomial equations were calculated for use in modeling applications. This study shows that concentration of bile acids in various body compartments varies significantly during the first 6 weeks posthatch.

Alterations in carotenoid metabolism during ochratoxicosis in young broiler chickens

The mechanism by which ochratoxin impairs the ability of chickens to utilize dietary carotenoids for carcass pigmentation was investigated. Graded doses of pure ochratoxin A (0, .5, 1.0, 2.0, and 4.0 micrograms of toxin/g of feed) were incorporated into a white corn-soy diet supplemented with an efficiently used oxycarotenoid (110 micrograms free lutein/g) and fed to broiler chicks from day of hatch to 3 weeks of age. Concentrations of free lutein and its metabolites, lutein diester, lutein monoester, and oxolutein, in the jejunal contents, jejunal mucosa, serum, liver, and toe web from these birds were measured by high performance liquid chromatography. Based on the threshold level of ochratoxin required for an effect on the concentrations of carotenoids and on the severity of the effect, five separate loci for the action of ochratoxin on carotenoid metabolism were detected: dilution of carotenoids in intestinal contents, depressed uptake by intestinal mucosa, depressed transport in serum, altered accumulation in liver, and altered acylation steps in the integument.

Histochemical characterization of glycoproteins present in jejunal and colonic goblet cells of pigs on different diets. A biopsy study using chemical methods and peroxidase-labelled lectins

We examined the glycoprotein composition of intestinal goblet cells in jejunal and colonic biopsies obtained from pigs on different diets. Paraffin sections were stained both chemically and with the following horseradish-peroxidase conjugated lectins: Canavalia ensiformis (Con-A), Limulus polyphemus (LPA), Lotus tetragonolobus (LTA), Arachis hypogaea (PNA), Ricinus communis (RCA1), Glycine max (SBA) and Triticum vulgaris (WGA). Using chemical staining procedures, only small quantitative differences were noted between the two organs. With respect to lectin staining, the mucus of the jejunum was characterized by the absence of Con-A binding sites, and colonic mucus consistently exhibited an absence of SBA affinity. After dietary modifications, O-acetyl sialic acid reactivity was lowered in the jejunum but was enhanced in the colon. In the jejunum, the glycoproteins became neuraminidase susceptible, whereas the colon became characterized by the absence of neutral mucins. The affinity for the tested lectins after the different diets was variable, but the most striking effects were observed after the fibreless diet (milk alone). Our data suggest the existence of marked regional variations in goblet-cell mucus and indicate significant differences between the glycoprotein components of the jejunal and colonic mucosa. Furthermore, the biosynthesis of mucins in both regions was altered by even only short-term feeding modifications.

The variation of Romhányi's aldehyde-bisulfite-toluidine blue (ABT)-reaction: the aldehyde-bisulfite-1.9-dimethyl methylene blue (ABD)- and sialic acid specific topo-optical reaction

The Aldehyde-Bisulfite-1.9-Dimethyl Methylene Blue reaction is a variant of Romhányi's Aldehyde-Bisulfite Toluidine Blue (ABT) reaction. The ABD reaction is also a selective topo-optical staining reaction of the vicinal (glycol) OH-groups in complex carbohydrates. According to polarization optical analysis, after the ABD-reaction we have found the oriented micellar textur of the glycoproteins in the microvillous layer of the human duodenum and jejunum. By means of the sialic-acid-specific topo-optical reaction, we have demonstrated that the sialic acid is present in an ordered form and is evenly distributed in the microvillous surface layer of duodenum and jejunum.

Framework of the enteric nerve plexuses: an immunocytochemical study in the guinea pig jejunum using an antiserum to S-100 protein

Immunostained sections and whole-mount preparations of the layers of the guinea pig jejunum were investigated by an improved peroxidase-antiperoxidase method using an antiserum to S-100 protein. A delicate latticework of S-100 protein immunopositive glial cells was demonstrated extending in the longitudinal muscle layer, myenteric or Auerbach's plexus, circular muscle layer including the deep muscular plexus, submucous layer including the submucous or Meissner's plexus, lamina muscularis mucosae and lamina propria mucosae. The whole enteric nerve plexuses consisted of two subsystems; nerve plexuses of the muscular coat and those of the submucous and mucous coats. These two subsystems were joined to each other by thick, connecting branches perforating the inner circular muscle layer. Extrinsic nerves entering the myenteric plexus formed a specialized junctional structure containing S-100 protein immunopositive glial cells, whereas those entering the submucous plexus ran along the submucous arteries. We proposed the term enteroglial cells to designate the S-100 protein immunopositive cells which ensheathed the somata and processes of the enteric neurons. The frameworks of all structures in the enteric nerve plexuses from the largest ganglia to the thinnest nerve fasciculi were constructed of these enteroglial cells. A spectrum of the enteroglial cells was presented. Those in the myenteric and submucous ganglia were found similar to the astroglia of the central nervous system and to the satellite cells in the peripheral ganglia. Those in the primary and secondary fasciculi of the myenteric plexus formed a kind of neuropil together with the neuronal processes. Those in the tertiary fasciculi of the muscular coat formed the framework of the autonomic ground plexus. We tentatively concluded that the interstitial cells of Cajal contain an immunoreactivity for S-100 protein, and thus are glial in nature. The occurrence of specialized enteroglial cells with a neuron-like function was discussed in the autonomic ground plexus of the muscular coat. In the lamina propria mucosae, there was a fine latticework of the S-100 protein immunopositive enteroglial cells. This latticework corresponded to that of the interstitial cells of Cajal in the villous and periglandular plexuses.

The subcellular distribution and levels of calmodulin in jejunal biopsies from control subjects and patients with coeliac disease

A radioimmunoassay has been established and validated for the estimation of calmodulin levels in human peroral jejunal biopsy samples. Total levels were similar in biopsies from control subjects and patients with coeliac disease, both in relapse and remission. The subcellular distribution of calmodulin was determined in biopsy samples from control subjects and a patient with coeliac disease in relapse by rapid single-step analytical subcellular fractionation and immunoassay. In both situations most (greater than 70%) of the calmodulin was recovered in the cytosolic fractions with no selective enrichment in any single organelle.

Isolation and characterization of a neurotensin-like decapeptide from a canine upper small intestinal extract

Neurotensin-like immunoreactivity can be detected in extracts of canine upper gastrointestinal mucosa when measured by carboxyl terminal but not by amino terminal antibodies to neurotensin. The nature of this immunoreactive material was characterized by complete purification on gel filtration and HPLC followed by peptide microsequence analysis. The structure obtained was Glu-Asn-Lys-Pro-Arg-Arg-Pro-Tyr-Ile-(Leu), identical in structure to the carboxyl terminal decapeptide of neurotensin. It cannot, however, be excluded that this neurotensin decapeptide was generated from a larger neurotensin-like peptide during the extraction procedure by a physiological or artificial enzymatic process. Since carboxyl terminal neurotensin fragments containing eight or more residues have full biological activity, this peptide may be responsible for neurotensin-like biological activities within the mucosa of, or after release from, the upper gut.

Pathogenesis of shigella diarrhea. XI. Isolation of a shigella toxin-binding glycolipid from rabbit jejunum and HeLa cells and its identification as globotriaosylceramide

A glycolipid that specifically binds shigella toxin was isolated from both HeLa cells and rabbit jejunal mucosa and identified as globotriaosylceramide (Gb3) by its identical mobility on HPTLC to authentic erythrocyte Gb3. Toxin also bound to a band tentatively identified as alpha-hydroxylated Gb3. In addition, toxin bound to P1 antigen present in group B human erythrocyte glycolipid extracts. The common feature of the three binding glycolipids is a terminal Gal alpha 1----4Gal disaccharide linked beta 1----4 to either Glc or GlcNAc. Globoisotriaosylceramide, which differs from Gb3 only in possessing a Gal alpha 1----3Gal terminal disaccharide, and LacCer, which lacks the terminal Gal residue of Gb3, were incapable of binding the toxin. Binding was shown to be mediated by the B subunit by the use of isolated toxin A and B subunits and monoclonal subunit-specific antibodies. Gb3-containing liposomes competitively inhibited the binding of toxin to HeLa cell monolayers but did not inhibit toxin-induced cytotoxicity. These studies show an identical carbohydrate-specific glycolipid receptor for shigella toxin in gut and in HeLa cells. The toxin B subunit that mediates this binding has also been shown to recognize a glycoprotein receptor with different sugar specificity. Thus, we have demonstrated that the same small (Mr 6,500) B subunit polypeptide has two distinctive carbohydrate-specific binding sites. The Gal alpha 1----4Gal disaccharide of the glycolipid toxin receptor is also recognized by the Gal-Gal pilus of uropathogenic E. coli. This suggests the possibility that the pilus and toxin B subunit contain homologous sequences. If this is true, it may be possible to use the purified Gal-Gal pilus to produce toxin-neutralizing antibodies.

Effect of age and diet on cyclic nucleotide concentrations in the intestinal mucosa of developing rats

Mucosa isolated from the proximal third of the small intestine of infant rats had much lower cyclic nucleotide concentrations (expressed both per unit wet weight and per unit DNA content) than those determined in the intestinal wall. The steady-state concentrations of both cyclic AMP and cyclic GMP in jejunum showed dramatic increases during the first 5 d post partum. Another increase in cyclic nucleotide concentrations was observed in the isolated mucosa between d 15 and 21. Starvation for 24 h always resulted in lower intestinal cyclic nucleotide concentrations than those of the fed littermates. This effect was more pronounced in younger animals and more evident for cyclic AMP values. Three-week-old rats fed a high carbohydrate diet for 24-48 h exhibited more pronounced elevations in the concentrations of cyclic nucleotides from the jejunal mucosa than did rats fed a high fat diet.

Effect of insulin and oral glutathione on glutathione levels and superoxide dismutase activities in organs of rats with streptozocin-induced diabetes

The effect of insulin or glutathione treatment on glutathione content of liver and jejunal mucosa and on superoxide dismutase (SOD) activity of liver, kidney, and erythrocytes was investigated in pair-fed animals with streptozocin (STZ)-induced diabetes. Diabetes lowered hepatic glutathione concentration, but glutathione concentration of the jejunal mucosa was not affected. Insulin, but not oral glutathione, restored hepatic glutathione concentration to normal levels. Diabetes depressed activity of the cytosolic form of SOD in liver, kidney, and erythrocyte. Treatment of diabetic rats with oral glutathione or intramuscular insulin increased cytosolic SOD activity of renal cortex and liver (but not erythrocytes) to control levels. These results suggest a link between glutathione metabolism and cytosolic SOD activity in diabetes.

Healing of esophagojejunal anastomoses after experimental total gastrectomy. A comparative study using manually sutured or stapled anastomoses

In construction of the eosphagojejunostomy after total gastrectomy, the EEA stapled (US Surgical Corporation, Norwalk, CT) and the two-layer interrupted 3-0 Dexon anastomoses are compared concerning the radiological appearance, breaking strength, circulation, and collagen concentration. Thirty female pigs were used. After total gastrectomy and Roux-en-Y preparation, the pigs were randomized to achieve sutured or stapled anastomoses. 141Ce-labeled microspheres were used for measurements of anastomotic blood flow. After the pigs were killed, the breaking strength of the anastomosis was recorded, the collagen content determined, and an anastomotic index calculated comparing two perpendicular diameters in the anastomosis and 5 cm above. Breaking strength, leakage frequency, and anastomotic index were the same in the two groups. One week after surgery, there was a significant increase in anastomotic circulation (p less than 0.05) in both the sutured and the stapled anastomoses compared to controls. Collagen increased equally with time in the two groups (p less than 0.01). The stapled esophagojejunostomy was faster to perform (20 min) than the sutured (28 min) (p less than 0.05).

Conversion of somatostatin-28 to somatostatin-14 during maturation of epithelial cells in the porcine jejunum

Fractions of isolated epithelial cells were harvested from a segment of porcine jejunum by ten successive incubations with a chelating buffer. The cell fractions showed a progressive decrease in the activity of the brush-border enzymes, alkaline phosphatase and sucrase, with increasing incubation number but a progressive increase in the ability to incorporate labelled thymidine into DNA. Fractions enriched in cells from the crypt region (fractions 9 and 10) contained higher concentrations per mg protein of somatostatin-like immunoreactivity (1.8-fold), glucagon-like immunoreactivity (5.3-fold) and serotonin (3.0-fold) than fractions enriched in cells from the villus tip (fractions 1 and 2). Analysis of extracts of the fractions by gel filtration/radioimmunoassay showed that somatostatin-28 represented the predominant molecular form of somatostatin-like immunoreactivity in all cell fractions but the relative proportion of somatostatin-14 (and related metabolites) to somatostatin-28 was significantly higher (P less than 0.05) in fractions enriched in villus cells (fraction 1 and 2) than in fractions enriched in crypt cells (fractions 5-10). This result suggests that metabolism of somatostatin-28 to somatostatin-14 takes place during migration of the D cell from the crypt base to the villus tip. Heterogeneity in the somatostatin-14 region of the chromatograms indicates that the peptide may be further metabolized by the action of aminopeptidases.