Inhibitory actions of loperamide on absorptive processes in rat small intestine.

Mucosal loperamide caused a dose dependent reduction in the absorption of actively transported hexoses and amino acids, together with the associated rise in short circuit current. Na+ and fluid movement were also inhibited. Serosal application of the drug was without effect on these processes. The passive movement of fructose across the gut was not affected by loperamide which is therefore unlikely to act by reducing tissue permeability. In low Na+ conditions the inhibitory actions of loperamide on glycine absorption were reduced. Loperamide reduced basal Na+ transport although it did not affect the stimulation of Na+ absorption caused by mannose. Loperamide had no effect on the total ATPase activity nor on the Na+, K+-ATPase activity of mucosal homogenates. The effects of loperamide were not mimicked by morphine nor were they antagonised by naloxone and hence do not seem to involve an opiate receptor. It is concluded that loperamide exerts its inhibitory effects by an interaction with the Na+ sites of the nutrient carriers.     

Influence of peppermint oil on absorptive and secretory processes in rat small intestine.

BACKGROUND: Peppermint oil is used to relieve the symptoms of irritable bowel syndrome, relaxing intestinal smooth muscle by reducing the availability of calcium, but its effects on intestinal transport are unknown. AIMS: To determine the effect of peppermint oil on intestinal transport processes. METHODS: The influence of peppermint oil on intestinal transport was investigated in rat jejunum using both intestinal sheets mounted in Ussing chambers and brush border membrane vesicles. RESULTS: Mucosal peppermint oil (1 and 5 mg/ml) had no significant effect on basal short circuit current, but inhibited the increase associated with sodium dependent glucose absorption. The increased short circuit current induced by serosal acetylcholine, a reflection of calcium mediated electrogenic chloride secretion, was unaffected by mucosal peppermint oil (5 mg/ml). In contrast, serosal peppermint oil (1 mg/ml) inhibited the response to acetylcholine without reducing the effect of mucosal glucose. In brush border membrane vesicles active glucose uptake was inhibited by extravesicular peppermint oil at concentrations of 0.5 and 1 mg/ml. CONCLUSIONS: Peppermint oil in the intestinal lumen inhibits enterocyte glucose uptake via a direct action at the brush border membrane. Inhibition of secretion by serosal peppermint oil is consistent with a reduced availability of calcium.     

Structural features of absorptive cell and microvillus membrane preparations from rat small intestine

Absorptive cells of the small intestine are highly polarized cells with distinct microvillus membrane (MVM) and basolateral plasma membrane domains. We compared membrane structure in the following preparations of rat small intestine commonly used for in vitro study of MVM function: epithelial sheets, isolated epithelial cells, and four different MVM vesicle preparations, using electron microscopy of thin sections and freeze fracture replicas. We also quantitated mean vesicle diameter of the four MVM preparations by quasielastic light scattering and determined their actin content. Epithelial sheets maintained their plasma membrane polarity as judged by intramembrane particle (IMP) distribution for at least 30 min after isolation. In contrast, the plasma membrane of isolated cells showed redistribution of IMPs, indicating considerable loss of polarity in the few minutes required for cell recovery. The P-face IMPs in MVM prepared by Ca++ precipitation were randomly distributed but became aggregated after exposure to potassium thiocyanate, which removed approximately 50% of core actin. The P-face IMPs in Mg++ precipitated MVM were aggregated whether or not core actin was depleted with potassium thiocyanate. The shape and size of MVM vesicles differed considerably with different preparative techniques. The extremely rapid loss of plasma membrane polarity of isolated intestinal epithelial cells and the striking structural heterogeneity of MVM vesicles prepared by commonly used techniques should be considered in the interpretation of functional studies with these preparations.     

移植小肠吸收功能的研究进展

小肠移植是治疗不可逆肠衰竭的有效方法.免疫抑制剂和外科技术的进步促进了小肠移植的临床应用,但移植小肠是否迅速恢复或达到自体小肠的功能水平,成为临床小肠移植的瓶颈.对营养物质的吸收是小肠重要的生理功能,了解移植后小肠的功能变化对预评价移植小肠的消化吸收能力和指导临床的术后干预具有重要意义.本文简要概括移植小肠吸收功能的研究现状,主要指标有移植小肠对水、电解质,糖,脂肪及蛋白质的吸收.     

Explant culture of human fetal small intestine

Human fetal intestine (10-14 wk gestation) has been cultured as explants in a serum-free Leibovitz L-15 medium for periods up to 9 days. As determined by light microscopy, the overall architecture of the intestinal explant was maintained throughout the culture period. At the ultrastructural level the villus absorptive cells remained tall with well-defined brush border, apical tubular system, and supranuclear and infranuclear accumulations of glycogen. All other epithelial cell types were also preserved. The incorporation of [3H]thymidine and [3H]leucine continued during the culture period, reflecting a sustained synthesis of deoxyribonucleic acid and proteins. The hydrolytic activities of the brush border membrane were established based on data obtained throughout the course of the culture of a large number of intestinal specimens. Sucrase, maltase, glucoamylase, trehalase, lactase, alkaline phosphatase, and gamma-glutamyl transpeptidase activities increased during the 9 days of culture even though different patterns were recorded. These observations clearly established that human fetal small intestine can be maintained in organ culture for at least 9 days in a serum-free medium.     

Lymphoid cell subsets in normal human small intestine

Nineteen specimens of normal tissue were obtained from the duodenum, upper jejunum and terminal ileum. Specimens were fixed with periodate-lysine-paraformaldehyde and then frozen sections were made. Lymphoid cell subsets were identified by indirect immunoperoxidase staining using mouse anti-human monoclonal antibodies. Results: There was a remarkable variation in the distribution of positive cells among individuals and even within single sections. Lymphoid cell subsets of the three parts of the small intestine were almost identical except for the difference in IgA subclasses of IgA-containing cells. IgA1 predominated over IgA2 in the jejunum while IgA2 predominated over IgA1 in the ileum. The subsets in the lamina propria (LP) and in the epithelium were clearly distinct; Leu 3+ (helper/inducer T) predominated in LP while Leu 2+ (suppressor/cytotoxic T) predominated in the epithelium and no Ig-containing cells were found in the epithelium. In LP the mean ratio of Leu 1+ (pan T):IgA (IgA1 + IgA2) containing cells: IgM: IgG: IgD: IgE: HNK-1+ was 48.9: 36.6: 9.0: 1.8: 1.0: 0.3: 2.4. The staining patterns of HLA-DR+ and Leu 10+ were similar; dense in the top in LP of the villi. In some individuals the apical portion of epithelial cells was stained by anti-HLA-DR. A few positive cells were observed in only two out of 19 cases by anti IL-2R.     

Electrical spike activity in the human small intestine

An intraluminal probe with 10 pairs of bipolar electrodes was used for continuous recording of myoelectric activity along the entire small intestine during 24 hr in 2 normal fasting human subjects. Two types of regular migrating activity were observed: (1) Bands of a great number of spike potentials appearing at hourly intervals migrating through the entire small intestine. This activity, corresponds to phase III of the interdigestive myoelectric complex described in animal experiments. (2) Bursts of a few spike potentials appearing with minute intervals migrating only through the jejunum. This activity has not previously been demonstrated in man nor in intact animals, but corresponds to the minute-rhythm described fromin vitro experiments.This study was supported by Danish Research Council and grants from Frk. P.A. Brandt's Legacy.     

Immunofluorescent localisation of enterokinase in human small intestine.

The distribution of enterokinase in human intestine was studied in operative mucosal biopsies using specific antiserum to human enterokinase, previously purified to apparent homogeneity by affinity chromatography and immunoabsorption. Fluorescence was observed in the brush-border and glycocalyx of the duodenum and proximal 15 cm of jejunum distal to the D/J flexure. Distal jejunum and ileum as well as stomach and colon were consistently negative. Brunner's glands and goblet cells were never stained by specific antibody. Preliminary evidence was obtained that the human enterokinase molecule contains a specific antigenic determinant in its polypeptide component and a second determinant in the oligosaccharide moiety which cross-reacts with blood group A. Preliminary evidence was also obtained that mucosal synthesis of enterokinase may be impaired in jaundice due to carcinoma of the pancreas and induced in the small intestine distal to the normal limit of synthesis after pancreatico-duodenectomy.     

Glucagon effects on the human small intestine

In healthy volunteers, the effects of intravenously administered glucagon on small intestinal function was investigated. Bolus doses resulting in plasma glucagon concentrations of >800 pg/ml (5 min after injection) abolished jejunal contractions for 4.4±0.4 (sem) min after a latency period of 49±4 sec. During continuous intravenous glucagon infusion, jejunal dilatation and increase in mean transit time (MTT) occurred at plasma levels >720 pg/ml, while inhibition of water and electrolyte absorption was observed only with plasma glucagon concentrations of 1760±114 pg/ml. Under these conditions, the propulsion of fasting intestinal contents was slowed without change in flow rate. The observed effects cannot be attributed to the simultaneously occurring rise in plasma insulin and glucose concentrations. Short-term increases in circulating glucagon concentration inhibit intestinal tone, contractions, and propulsion with only a minor effect on water and electrolyte absorption limited to a narrow concentration range of plasma glucagon. Neither effect occurs at glucagon levels likely to occur under physiologic concentrations. The latency period preceding the abolition of jejunal contractions suggests that glucagon does not act directly on intestinal smooth muscle cells.Presented in part at the Annual Meeting of the American Federation for Clinical Research, Midwestern Section, Chicago, Illinois, November 4, 1971, and at the Annual Meeting of the American Gastroenterological Association, Dallas, Texas, May 25, 1972; published in part in abstract form (1, 2).This work was supported by the Medical Research Service of the Verterans Administration and grant #AM-12985 from the National Institute for Arthritis, Metabolism and Digestive Diseases, National Institutes of Health, Bethesda, Maryland.     

Cyclic AMP-dependent anion secretion in human small and large intestine

Cyclic AMP-dependent Cl secretion is the major secretion pathway in human intestine. The aim of the present study was to examine mechanisms involved in cAMP-dependent anion secretion in human small and large intestine. Surgical resection specimens from both jejunum and distal colon were studied under short circuited conditions. Addition of the phosphodiesterase inhibitor IBMX induced an increase in the short-circuit current (Isc) equivalent to the net increase in Cl secretion. The Isc was inhibited by diphenylamine decarboxylate (DPC; Cl channel blocker), bumetanide (basolateral Na⁺/K⁺/2Cl cotransporter), BaCl₂ (basolateral K⁺ channel) and Cl free buffer in both segments and indomethacin (cyclo-oxygenase inhibitor) in colon alone. Diphenylamine decarboxylate appears to directly inhibit secretion in jejunum, although its inhibitory effect is possibly mediated by inhibition of cyclo-oxygenase in the colon. A small component of IBMX-stimulated Isc was inhibited by acetazolamide. Cyclic AMP-dependent secretion is largely apical Cl secretion, although a small component appears to be HCO₃. Secretion is dependent on basolateral K⁺ channels and Na⁺/K⁺/2Cl cotransporters and, in the colon, is inhibited by indomethacin, implying a role for cyclo-oxygenase metabolites. The chloride channel blocker DPC inhibits secretion in both areas. This class of compounds may have potential for treatment of secretory diarrhoea.     

Phytase activity in the human and rat small intestine.

Phytate is the major storage form of phosphorus in seeds and so is a common dietary constituent. Excessive ingestion of undegraded phytates can cause mineral deficiencies in humans. In addition, phytic acid is antineoplastic in animal models of both colon and breast carcinoma. There have been no previous studies quantifying phytase activity in the human small intestine although it is present in animals. Small intestinal phytase and alkaline phosphatase activity and distribution was measured in vitro in mucosal homogenates from two human small intestinal specimens obtained from transplant donors. Rat intestine was also studied for comparison. Phytase activity was found in human small intestine at low values (30 times less than that in rat tissue and 1000-fold lower than alkaline phosphatase in the same tissue). The activity was greatest in the duodenum and lowest in the ileum. In conclusion, the normal human small intestine has very limited ability to digest undegraded phytates. Although this may have adverse nutritional consequences with respect to metabolic cation imbalances, the presence of undigested phytate in the colon may protect against the development of colonic carcinoma.     

Quantitative analysis of motility recordings in the human small intestine

Simultaneous records of intraluminal pressure and electrical-action potentials (spike potentials) in the human duodenum were analyzed quantitatively by means of a stepwise scale of increasing activity, considering the frequency of spike potentials in combination with the frequency, duration, and amplitude of pressure waves. The analysis of consecutive 50-second periods was set up in a chart which can also be prepared in the form of a punched card representing an ultrashort summary of the intestinal motor activity throughout the entire examination. The abovementioned quantitative classification was related to visible motor activity by means of synchronized cinefluorography. The system described for quantitative motor analysis in the gastrointestinal tract is fast and easy to practice and may be useful for clinical motility studies.