Regulation of glucose homeostasis in rat jejunum by despentapeptide-insulin in vitro.

The regulation of the absorption and metabolism of glucose in rat small intestine by insulin was studied by the perfusion of isolated loops of proximal jejunum in vitro. The addition of an active, monomeric form of insulin, despentapeptide-insulin, to the serosal side of the intestine from normal rats inhibited luminal glucose absorption (421 (11) to 285 (11) mumol/h/g dry wt, p less than 0.001) and lactate production (340 (28) to 192 (26) mumol/h/g dry wt, p less than 0.001), but had no effect on glucose utilisation (231 (11) and 210 (16) mumol/h/g dry wt). The production of acute insulin deficiency by the injection of anti-insulin serum in vivo caused a marked inhibition of luminal glucose absorption (421 (11) to 240 (13) mumol/h/g dry wt, p less than 0.001), glucose utilisation (231 (11) to 48 (2) mumol/h/g dry wt, p less than 0.001) and lactate production (340 (28) to 94 (2) mumol/h/g dry wt, p less than 0.001) in vitro. The effects of insulin deficiency were reversed by despentapeptide-insulin in vitro, so that the rates of absorption and metabolism for intestine from insulin deficient and normal rats were similar in the presence of the modified insulin. All the effects caused by insulin deficiency and despentapeptide-insulin were apparent within minutes and could not be attributed to hyperglycaemia. It is concluded that rat small intestine is subject to rapid and direct regulation by insulin.     

Acute exposure of rabbit jejunum to ethanol

The effect of acute exposure of rabbit jejunum to ethanol on the uptake of three hexoses was examinedin vitro. With ethanol present in the preincubation medium for 30 min, or directly in the incubation medium for 6 min, glucose uptake was reduced. Kinetic analysis demonstrated that ethanol in the preincubation medium was associated with a rise in the value of the apparent Michaelis constant (K _m ^*), whereas the inhibition of glucose uptake observed with ethanol present directly in the incubation medium was associated with a reduction in the apparent passive permeability coefficient (P _d ^*), a reduction in the maximal transport rate (J _d ^m ), and an increase inK _m ^*. When increasing concentrations of ethanol were added to the preincubation or to the incubation medium, there was a reduction in the uptake of both 1 mM and 40 mM glucose, galactose, and 3-O-methyl glucose. The addition of 40 mM galactose or 1 mM phloridzin to 40 mM glucose was associated with a 50% reduction in glucose uptake, but this uptake was not further inhibited by the addition of 6% ethanol (v/v). Similarly, the uptake of 3-O-methyl glucose was inhibited by the addition of 40 mM glucose or galactose but no further reduction in uptake was achieved by adding ethanol. Finally, galactose uptake was inhibited by adding 40 mM glucose or 40 mM 3-O-MG, but the addition of 6% ethanol was associated with no further decline in the uptake of galactose. Previous studies have shown that ethanol has no effect on the effective resistance of the intestinal unstirred water layer when the bulk phase is stirred; thus the ethanol-related changes inK _m ^* andP _d ^* are associated with qualitatively similar changes in the values of the true Michaelis constant,K _m , and the true permeability coefficient,P _d . In summary, ethanol has a complex effect on the intestinal uptake of hexoses, influencing theK _m ,J _d ^m andP _d , but the type and extent of inhibition depends upon whether the intestine has previously been exposed to ethanol, or whether the ethanol is presented to the intestine concurrently with the hexose.     

Aging and cholesterol uptake in the rabbit jejunum

A previously validatedin vitro technique was used to determine the effect of aging upon the rate of uptake of cholesterol into the jejunum of suckling, young, and older rabbits. Cholesterol uptake was greater in suckling than in older animals, over a wide range of durations of incubation and varying concentrations of cholesterol or bile acid. The rate of uptake of cholesterol in the young animals was intermediate between the values seen in the suckling and older rabbits. This greater uptake of cholesterol in the younger than in the older animals persisted when the effective resistance of the unstirred water layer (UWL) was varied by stirring the bulk phase. In contrast, the uptake of medium- and long-chain length fatty acids was greater in the young than in the older animals when UWL was low, but the converse was true when UWL was high at each rate of stirring of the bulk phase. The UWL was lower in the younger than in the older rabbits. Thus, the differences in thein vitro uptake of cholesterol into the jejunum of rabbits of varying age is due to the greater passive permeability properties and greater functional membrane surface area of the jejunum of young animals, and the lower effective resistance of the overlying unstirred water layer.With the technical assistance of B. Philips, M. Yuen, K. Marshall, and C. Hotke.Financial support was derived from funds granted by the Medical Research Council.     

Uptake of lipids into rabbit jejunum and colon following Ileal resection

This study was undertaken to determine the effect of variations in the dietary content of carbohydrate (sucrose) and intestinal resection on the passive jejunal and colonic uptake of short-, medium-, and long-chain length fatty acids, cholesterol, and decanol. A previously validated in vitro technique was used, and studies were performed in sham-operated control animals and in rabbits submitted to the surgical removal of the distal half of the small intestine. After six weeks feeding of a high- or low-carbohydrate diet, the uptake of lipids was altered, but the direction and extent of changes was different among jejunum, ileum, and colon in control animals, and between the jejunum or colon of control vs resected animals. The intestinal membrane is likely heterogeneous with respect to passive permeability pathways since dietary manipulation of sucrose had a different effect on the uptake of each lipid probe. The finding of lower jejunal and colonic cholesterol uptake in animals fed a high- as compared with a low-carbohydrate diet reflects the importance of dietary effects on intestinal permeation. Studies must now be performed to establish the mechanisms responsible for these diet-related changes in intestinal permeability.     

Enhanced glucose absorption in the jejunum of patients with cystic fibrosis

After oral D-xylose ingestion, cystic fibrosis patients have significantly higher blood levels of xylose than controls. The aim of this study was to examine whether nutrient absorption at the mucosal level is altered in cystic fibrosis. Steady-state perfusion experiments using isotonic test solutions were performed in 11 healthy controls and 10 cystic fibrosis patients. Net D-glucose absorption was higher in cystic fibrosis when the perfusate contained a glucose concentration of less than or equal to 50 mM. Kinetic analysis by three different methods, including Lineweaver-Burk analysis, revealed a lower apparent Km as well as a lower apparent Vmax in cystic fibrosis as compared with healthy controls (33.9 mM and 52.5 mmol/20 cm . h vs. 81.8 mM and 68.3 mmol/20 cm . h, respectively, p less than 0.01). Absorption of D-fructose and glycine demonstrated a tendency for increased net absorption in cystic fibrosis but the results were not significantly different. L-Xylose absorption and electrolyte movement were not altered in cystic fibrosis. Among several possible mechanisms investigated, a decrease in the apparent Km for glucose absorption would be consistent with a decrease in diffusion barriers overlying the jejunal mucosa in cystic fibrosis. Using an electrical method, the unstirred water layer thickness was significantly decreased in cystic fibrosis (546 +/- 41 micron in cystic fibrosis vs. 780 +/- 110 micron in controls, p less than 0.05). A decrease in the mucosal surface area in the cystic fibrosis group or an intrinsic defect in the mucosal glucose transport system could account for differences in the apparent Vmax values. We suggest, however, that enhanced absorption in cystic fibrosis is most likely due to a decrease in intestinal diffusion barriers possibly due to abnormal mucus overlying the intestinal mucosa.     

Mucin and protein release in the rabbit jejunum: effects of bethanechol and vagal nerve stimulation.

The role of the vagus nerve and cholinergic mechanisms in the control of rabbit jejunal mucin and protein release was investigated in vivo. In anesthetized animals, a 10-cm segment of the jejunum was cannulated and perfused with saline. Perfusate was collected and analyzed for mucin (by immunoassay) and protein. Bilateral cervical vagotomy had no effect on basal mucin or protein output, suggesting that the vagus nerve does not exert a tonic control on jejunal macromolecule secretion. Electrical stimulation of the vagi did not alter mucin release, even in the presence of muscarinic cholinergic (scopolamine) or adrenergic (propranolol and phentolamine) blockade. In contrast, protein output increased significantly after vagal stimulation, an effect inhibited by scopolamine. In both vagotomized and vagally intact rabbits, the cholinergic agonist bethanechol (200 micrograms/kg intraperitoneally) induced a scopolamine-sensitive increase in both mucin and protein output. Predominantly serum proteins were released into intestinal perfusates after vagal or cholinergic stimulation. It is concluded that the extrinsic vagus nerve does not regulate rabbit jejunal mucin secretion in vivo and that cholinergic control of intestinal goblet cells is implemented entirely by the intrinsic enteric nervous system. In addition, cholinergic or vagal stimulation increases intestinal vascular and epithelial permeability, resulting in the passage of serum proteins into the lumen, possibly by opening tight junctions and paracellular pathways.     

Ethanol-induced inhibition of glucose transport across the isolated brush-border membrane of hamster jejunum

Acute exposure of jejunal mucosa to ethanol has been reported to produce a depression of transmural glucose transport across this organin vitro andin vivo. In an attempt to understand the mechanism of action of ethanol on intestinal transport, in the present study we have investigated the effect of ethanol on glucose uptake by purified brush-border membrane vesicles of hamster jejunum. Ethanol, in concentrations found in man after moderate drinking (1–5% w/v), was found to depress glucose uptake by the brush-border membrane in a dose-dependent and time-dependent manner. Mannose was used to measure nonspecific uptake, and we found that the ethanol-induced depression of glucose uptake was not related to an alteration of the nonspecific uptake of this sugar. The inhibition of glucose uptake of the ethanol-treated membranes completely disappeared after repeated washing of the membranes with ethanol-free buffer. Accordingly, the ethanol-induced depression of glucose uptake was not the result of irreversible damage to membrane proteins but was related to a direct effect of ethanol on the brush-border membrane. On the basis of these findings, it is concluded that a direct interference with glucose translocation across the brush border plays an important role in the ethanol-induced depression of transmural jejunal glucose absorption.

     

Cellular mechanism underlying LPS-induced inhibition of in vitro L-leucine transport across rabbit jejunum

Lipopolysaccharide (LPS) is a known causative agent of sepsis. In previous studies, we have shown that it reduces L-leucine mediated transport across the rabbit jejunum by about 30%. In this study, the mechanism(s) of LPS inhibition on amino acid transport were analysed in detail. LPS did not inhibit L-leucine transport across brush border membrane vesicles, suggesting the need for an intracellular step. The inhibitory effect of LPS was not altered by the addition of protein kinase A (PKA) inhibitor (IP(20), 10(-7) M) or an analog of cAMP (DB-cAMP, 3 x 10(-4) M), indicating that the PKA signal transduction pathway was not involved in the LPS effect. However, the inhibitory effect of LPS was suppressed by trifluoroperazine (10(-7) M), a Ca(2+)/calmodulin inhibitor and staurosporine (10(-7) M), an protein kinase C (PKC) inhibitor. Likewise, LPS inhibition disappeared in media without calcium. These results suggest that LPS could inhibit the intestinal uptake of L-leucine across the small intestine in vitro by intracellular processes related to calcium, involving PKC and calmodulin protein.     

Selenium absorption by canine jejunum

Deficiency of the trace element selenium causes disease in domestic animals and may also be implicated in the pathogenesis of some human itlness. In this study, the triplelumen perfusion method was used to measure the rate of absorption of trace quantities of selenium (50 g/liter in a physiological electrolyte solution) from the jejunum when given asd,l-selenomethione,d,l-selenocystine, or sodium selenite to healthy dogsin vivo. Selenium absorption from the test segment (expressed as percent administered dose per centimeter±sem) was 1.97±0.04 fromd,l-selenomethionine, 1.15±0.06 fromd,l-selenocystine, and 0.51±0.07 from sodium selenite (P<0.01,N=5). In separate studies in four anesthetized dogs, the jejunum was perfused withl-[⁷⁵Se]selenomethionine while concentrations of⁷⁵Se were measured in the portal venous blood; these studies established that [⁷⁵Se]selenomethionine disappearing from the gut lumen corresponded quantitatively to⁷⁵Se appearing in the portal venous effluent (74±6%) and incorporated into intestinal tissue (24±5%). These results are consistent with the hypothesis that the absorption of amino acid-bound selenium is accelerated by the specific amino acid active transport mechanisms in the gut mucosa. Sodium selenite is absorbed more slowly, possibly by simple diffusion through the intestinal mucosa, than the amino acid-bound selenium compounds.Financial assistance was received from the Medical Research Council of New Zealand, the Medical Research Distribution Committee, the Telford Trust and the Medical Research Service of the Veterans Administration.     

5-hydroxytryptamine release into human jejunum by cholera toxin.

BACKGROUND: Cholera toxin produces intestinal secretion by activation of the adenylate cyclase complex. However animal studies have shown 5-hydroxytryptamine may be released after exposure to cholera toxin, and thereby contribute to the secretory state. AIM: To determine whether cholera toxin releases 5-hydroxytryptamine in human jejunum. SUBJECTS: Seven male subjects were given a subclinical dose of cholera toxin in a paired, controlled, randomised, double blind study. METHODS: A closed 10 cm segment of upper jejunum was exposed to 15 micrograms of cholera toxin for two hours prior to closed segment perfusion with plasma electrolyte solution containing a non-absorbable volume marker, [14C]-polyethylene glycol. 5-Hydroxytryptamine in jejunal effluent and 5-hydroxyindoleacetic acid in urine (up to seven hours after cholera toxin) were measured by high performance liquid chromatography with fluorimetric detection. RESULTS: In contrast with controls, all subjects secreted fluid in response to cholera toxin, median-2.1 ml/cm/h (interquartile range-4.1 to -0.1). During seven hours following cholera toxin, 5-hydroxytryptamine was secreted into the lumen (range 31 to 395 nmol/l) but not in control experiments. After exposure to cholera toxin median urinary 5-hydroxyindoleacetic acid was 5.7 (4.1 to 6.3), which was similar to controls 4.9 (4.1 to 6.3), which was similar to controls 4.9 (4.1 to 6.2). CONCLUSION: Thus, cholera toxin induced a secretory state and promoted the release of 5-hydroxytryptamine into the intestinal lumen, but quantitative changes in urinary 5-hydroxyindoleacetic acid were not detectable. As an intestinal secretagogue, these findings suggest that 5-hydroxytryptamine may play a part in mediating cholera toxin induced secretion in humans.     

Primary malignant hemangioendothelioma of jejunum.

Primary malignant hemangioendothelioma is a rare tumor. We report a patient with a malignant jejunal hemangioendothelioma which had metastasized to the regional lymph nodes and the liver.     

Dieulafoy's lesion of the jejunum.

Dieulafoy's lesion is a rare vascular anomaly but a potentially life-threatening disease. This lesion can also be found in the small intestine, which can be diagnosed only by angiography. However, the angiography may be normal when the bleeding is inactive. We report a case of jejunal Dieulafoy's lesion with a repeated attack of massive gastrointestinal bleeding with a normal initial angiography. The pathological examination found an unusual picture as a dilated submucosal vessel protruded like a submucosal tumor.     

The ontogeny of the rabbit brain glucose transporter

We investigated the presence of three specific types of glucose transporters (GT) within the rabbit central nervous system during various developmental stages. Employing the Hep G2/brain-type insulin-insensitive and the insulin-responsive (IRGT; adipocyte/skeletal muscle type) GT antibody and cDNA, we studied protein and mRNA within the whole brain (25-, 27-, and 30-day-old fetus; 1-, 5-, 10-day-old neonate; and adult), using cultured neuronal and glial cells, by Western and Northern blot analysis. Similarly, using the insulin-insensitive human fetal skeletal muscle-type (GLUT-3) GT cDNA, we characterized this mRNA by Northern blot analysis. Additional confirmation of cell specificity was sought by performing immunohistochemical staining on the neuronal and glial cells to detect the specific type of GT protein. We observed a developmental regulation of brain-type GT within the whole brain, the peak abundance of protein and mRNA occurring in the adult, followed next by the fetus. No IRGT was detected within the whole brain at any stage of development. Contrary to the brain-type GT mRNA, GLUT-3 mRNA was found to be most abundant in the 10-day-old neonate and adult, followed next by the early neonate, with little in the fetus. Within isolated brain cell cultures, the mRNAs for the brain- and GLUT-3-types of GTs were abundantly present within glial cells, with considerably lesser amounts noted within the neurons. IRGT, on the other hand, revealed rather weak mRNA bands in both glial and neuronal cells. Western blotting revealed a brain type of GT protein within the glial cells alone; the neuronal cells for the most part were devoid of both the brain-type and the IRGT proteins. Further immunohistochemical staining confirmed the definite presence of the brain-type GT within the glial cells, with slight immunoreactivity observed within the neurons. Additionally, no significant IRGT immunoreactivity was observed within either cell type. We did not study the GLUT-3 type of immunoreactivity within neurons and glia. We conclude that both the Hep G2/brain and the GLUT-3 types, and not the IRGT, are developmentally regulated within the whole brain. Further, the Hep G2/brain and the GLUT-3 types of GTs are distinctly present within glial cells, with none to minute amounts present within the neurons. No IRGT protein is observed within the whole brain and the two cell types. These results suggest a differential expression of specific GT types within the neuronal and glial components of the brain.     

Different response of gastric inhibitory polypeptide to glucose and fat from duodenum and jejunum

Gastric inhibitory polypeptide (GIP), insulin, and blood glucose after ingestion of glucose or fat were examined in patients after gastrectomy with esophagojejunostomy or esophagoduodenostomy. After a glucose load patients without duodenal passage had significantly higher glucose and significantly smaller insulin levels than patients with duodenal passage. The fasting levels of serum immunoreactive GIP were moderately elevated and reached significantly higher levels after oral glucose ingestion in both gastrectomized groups as compared with normal subjects. In patients with preserved duodenal passage serum IR-GIP levels peaked earlier and were significantly higher than in patients without duodenal passage. In contrast to the finding after oral glucose ingestion, the IR-GIP response to an oral fat load was nearly twofold greater in patients without duodenal passage than in patients with duodenal continence. Thus, glucose-induced GIP release is mainly of duodenal and fat-induced GIP release mainly of jejunal origin. This suggests the existence of two types of GIP cells.     

Unstirred layer and kinetics of electrogenic glucose absorption in the human jejunum in situ

Using an electrical technique we estimated the thickness of the unstirred layer in the human jejunum during kinetic studies of electrogenic glucose absorption. The unstirred layer in seven healthy volunteers (632 +/- 24 mum: mean +/- SEM) was significantly thicker than in 10 patients with active coeliac disease (442 +/- 23 mum) but not significantly different in seven patients who had responded to treatment by gluten withdrawal (585 +/- 49 mum). There were similar differences in the values of ;Apparent Km' for electrogenic glucose absorption between healthy control subjects (36 +/- 6 mM) active coeliac patients (11 +/- 1 mM) and treated coeliac patients (31 +/- 5 mM). The changes in PDmax however, showed a different pattern. The PDmax in the active coeliac group (6.8 +/- 0.7 mV) was lower than in controls (7.6 +/- 0.6 mV) but not significantly so, while the PDmax in the treated coeliac group (10.6 +/- 0.9 mV) was significantly higher than in both the active coeliac and control groups. It should be noted that both operational kinetic parameters obtained in the present study are much lower than those obtained previously (Read et al., 1976b) because of the use of siphonage. Analysis of the results using a computer simulation indicates that the reduction in Apparent Km in active coeliac disease can be caused by the interaction of the decreased maximal absorption rate for glucose (Jmax) with the attenuated unstirred layer. In these circumstances it is not necessary to postulate any change in the affinity of the transport mechanism for glucose (;Real Km'). It is remarkable that the disease process produces an Apparent Km which is much closer to the Real Km than that found in health.     

Regional localization of activity of Clostridium perfringens type A enterotoxin in the rabbit ileum, jejunum, and duodenum.

Rabbit ileal, jejunal, and duodenal loops were exposed to purified enterotoxin from Clostridium perfringens type A and then perfused for comparative analysis of effects of the enterotoxin on each region of the intestine. Ileal loops responded with enhanced net secretion of fluid and sodium, inhibition of chloride and glucose uptake, and substantial sloughing of epithelial cells. The jejunum responded with fluid secretion, enhancement of sodium secretion only during the first 20 min, inhibition of chloride and glucose uptake, and substantial sloughing of epithelial cells. In the duodenum, transport of fluid, sodium, and chloride was significantly altered only during the first 20 min of perfusion, and significant inhibition of glucose uptake varied from one period to another. Epithelial damage was much less than that seen in the jejunum or ileum. Levels of fluid protein in all three sections corresponded closely to extent of tissue damage. In general, it was found that the severity of response to fixed doses of enterotoxin varied as follows: ileum greater than jejunum greater than duodenum.