Zymosan-induced bacterial translocation: a study of mechanisms

BACKGROUND AND METHODS

At nonlethal doses, zymosan induces a systemic inflammatory state and promotes bacterial translocation. This study was performed to investigate the mechanisms by which zymosan causes intestinal mucosal injury and bacterial translocation. Bacterial translocation to the mesenteric lymph node was measured 24 hrs after intraperitoneal challenge with saline or zymosan (0.1 mg) in normal (CD-1), congenitally macrophage-hyporesponsive (C3H/HeJ), complement-deficient (DBA/2), or mast cell-deficient (W/Wv) mice. Since zymosan-induced bacterial translocation may be mediated by xanthine oxidase-generated oxidants, bacterial translocation was measured in mice pretreated with the xanthine oxidase inhibitor, allopurinol. To further investigate the role of oxidants in zymosan-induced bacterial translocation, ileal and hepatic levels of xanthine oxidase, myeloperoxidase, conjugated dienes, malondialdehyde, and the antioxidants--superoxide dismutase, catalase, and glutathione peroxidase, were measured.

RESULTS

Zymosan-induced mucosal injury and bacterial translocation occurred to a similar extent (p less than .05) in all four genetic strains of mice, but were reduced in the mice pretreated with allopurinol. Zymosan increased (p less than .03) ileal and hepatic xanthine oxidase activity, while reducing (p less than .01) antioxidant (catalase) activity. There was also evidence of hepatic, but not ileal, lipid peroxidation (conjugated diene) (p less than .05) and neutrophil sequestration (myeloperoxidase) (p less than .01).

CONCLUSIONS

Zymosan-induced intestinal mucosal injury and bacterial translocation do not require complement activation, or the release of macrophage or mast cell products. They appear to be mediated by xanthine oxidase-generated products and associated with disruption of the normal ileal and hepatic oxidant-antioxidant balance.

Collagenolytic activity in experimental intestinal anastomoses. Differences between small and large bowel and evidence for the presence of collagenase

Collagen degradation is thought to be an integral part of the healing sequence of intestinal anastomoses, but almost nothing is known about the enzyme activities involved. We have studied collagenolytic activities, extracted from 1 day-old intestinal anastomoses in the rat. Using either soluble type I collagen or fibrillar type I or type III collagen as a substrate, activities measured in extracts from anastomotic segments were compared to those in extracts from uninjured intestine, removed at operation: in all cases, the collagenolytic activity in anastomotic extracts was significantly higher. This increase was significantly more pronounced in large bowel than in small bowel. The activities were strongly inhibited by serum and metallo-chelating compounds. Analysis, by means of SDS-polyacrylamide gel electrophoresis, of the reaction products of the degradation of fibrillar type I collagen by the extracts revealed the presence of a multitude of fragments, amongst them TcA fragments characteristic for the activity of mammalian collagenase. Thus, the degradative capacity towards various collagen substrates is enhanced in the anastomotic area during the first postoperative period and a true mammalian collagenase is one of the enzymes present.

Altered regulation of regional sucrase-isomaltase expression in diabetic rat intestine

Increased sucrase-isomaltase (SI) expression is a prominent feature of adaptive changes observed in the small intestine of streptozocin-treated chronically diabetic (CD) rats. In this study, we examine the cellular and molecular basis of increased SI expression in CD rats by determining SI specific activities and mRNA abundance in sequentially isolated enterocytes along the villus-to-crypt axis of proximal jejunum and distal ileum. In all regions, two- to fourfold increases in sucrase activity in diabetic rat enterocytes were paralleled by increases in SI mRNA. However, analogous to nondiabetic rat intestine, no differences in SI mRNA abundance were observed between corresponding enterocyte fractions from ileum and jejunum of diabetic rat intestine. By nuclear run-on assays, differences in rates of SI gene transcription were not observed in diabetic and nondiabetic intestinal tissues. We conclude that diabetes induces increased total and specific activities and mRNA abundance of intestinal SI, largely through the stabilization of SI mRNA. Furthermore, analogous to nondiabetic small intestine, differences in proximal-to-distal SI expression appear to be determined at the translational or posttranslational level.

Effects of amino acids in mixtures given by enteral or parenteral route on intestinal morphology and hydrolases in rats

This study compares the effects of amino acid addition to an elemental liquid diet containing carbohydrates and triglycerides given either intragastrically or intravenously on the morphology and on hydrolase activities in the jejunum and ileum of adult rats. The isocaloric mixtures were administered for 4 days and control rats received an isocaloric laboratory diet orally. Independent of their content in amino acid, all mixtures given intravenously caused a drop in mucosal weight and a shortening of the height of the villi in both the jejunum and ileum. By enteral route, the addition of amino acids to a carbohydrate-triglyceride liquid diet led to the maintenance of normal villus height (this effect being prominent in the ileum) and to a significant increase of jejunal sucrase and aminopeptidase activities when compared with the carbohydrate-triglyceride mixture. Feeding the mixtures by parenteral route caused a significant drop of both enzyme activities. In contrast, lactase activity was generally not modified by the route of nutrient administration or by the composition of the diets. However, the absence of amino acid in the mixture given intravenously caused a specific drop of lactase activity in the ileum. Ileal sucrase activity was lowered dramatically by intragastric or intravenous feeding of the elemental diets. This effect was not modulated by the presence of amino acids. The presence of amino acids caused a significant drop of aminopeptidase activity in the ileum independently of the route of administration when compared with animals receiving the carbohydrate-triglyceride liquid diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminopeptidase activity in the jejunal and ileal Peyer's patches of the albino rabbit

The objectives of this study were (a) to compare the aminopeptidase activity in the Peyer's patches of the jejunum and ileum of the albino rabbit against that in the adjacent patch-free segments and (b) to determine the relative sensitivities of the aminopeptidase activity in the Peyer's and non-Peyer's patches to aminopeptidase inhibitors and penetration enhancers. The results indicated that the Peyer's patches were about equal in aminopeptidase activity in the jejunum and in the ileum but were only 20-30% as rich in aminopeptidase activity as their neighboring patch-free areas. Compared to non-Peyer's patches, the aminopeptidase activity in the Peyer's patches was not as sensitive to the inhibitory effect of amastatin. It was, however, much more sensitive to the inhibitory effect of puromycin and p-chloromercuribenzoate and was somewhat more sensitive to the inhibitory effect of Na deoxycholate, Na glycocholate, and polyoxyethylene-9-lauryl ether. Therefore, based on substrate preferences and on the relative sensitivity of aminopeptidase activity to inhibition by aminopeptidase inhibitors and penetration enhancers, the relative proportions of various aminopeptidases in the Peyer's patches and in the non-Peyer's patches are likely different.

Effects of oral supplementation of glutamine on small intestinal mucosal mass following resection

Following massive small bowel resection, the remaining small bowel increases in mucosal weight, protein, deoxyribonucleic acid (DNA) content and absorptive function. Enteral nutrients are known to be important in stimulating this response. Recently, glutamine has been described as an essential fuel for the small intestinal mucosa and is thought to be trophic to the small bowel. We investigated if glutamine, when added to the diet in large quantities, might stimulate mucosal adaptation beyond that which normally occurs following physiologic feedings. Male Sprague-Dawley rats were placed on powdered rat chow supplemented with either 5% glutamine, 5% glycine or 5% glucose. After 4 days rats underwent 70% jejunoileal resection. Fourteen days after resection, protein, DNA and sucrase activity in the duodenum of the glutaminefed animals were all significantly lower than results from both the glycine and glucose groups. Duodenal mucosal weight was lower in the glutamine group than in the glycine group. In the ileum, DNA content was significantly lower for the glutamine group than the glycine group. These results suggest that high concentrations of glutamine in the diet can have negative effects on intestinal adaptation.

Alterations in quantitative distribution of Na,K-ATPase activity along crypt-villus axis in animal model of malabsorption characterized by hyperproliferative crypt cytokinetics

The distribution of sodium- and potassium-stimulated ATPase (Na,K-ATPase) along the crypt-villus axis and crypt cytokinetics were examined in an infective model of celiac disease produced by infection of the rat with the nematode Nippostrongylus brasiliensis. In controls, levels of enzyme activity remained stable during enterocyte migration to the villous apex. In the jejunum of infected rats, the structural lesion of villous atrophy and crypt hyperplasia, observed at day 10 of infection, was associated with a three-dimensional expansion of the crypts. Cell cycle time was shortened and this resulted in a markedly increased crypt cell production rate. Enterocytes emerged from the crypts at a faster rate, and this functional immaturity was paralleled by decreased Na,K-ATPase activity. Further decreases in enzyme levels were observed during enterocyte migration along the villi. This may reflect enterocyte damage or increased enzyme turnover. In the ileum of these animals, enterocyte maturation was prolonged and enzyme activity was increased at the level of the crypt villus junction with further increases noted during enterocyte transit. These changes in ileal Na,K-ATPase appear to be adaptive.

Induction of early-phase tolerance to endotoxin-induced mucosal injury, xanthine oxidase activation, and bacterial translocation by pretreatment with endotoxin

The goal of this study was to determine whether tolerance would develop to endotoxin-induced mucosal injury, xanthine oxidase activation, and bacterial translocation. To accomplish this goal, four groups of mice were studied: 1) mice receiving ip injections of saline 96 and 24 hr prior to sacrifice, 2) mice receiving ip injections of saline 96 and endotoxin (0.1 mg) 24 hr prior to sacrifice, 3) mice receiving ip injections of endotoxin 96 and 24 hr prior to sacrifice, and 4) mice receiving ip injections of endotoxin 96 hr and saline 24 hr prior to sacrifice. In contrast to the saline control animals or mice sacrificed 96 hr after a single dose of endotoxin, mice sacrificed 24 hr after receiving a single dose of endotoxin had evidence of mucosal injury, elevated levels of ileal xanthine oxidase activity, and an 81% incidence of bacterial translocation. Mice sacrificed 24 hr after a second dose of endotoxin were largely protected against the toxic effects of endotoxin. Thus tolerance to endotoxin-induced bacterial translocation does develop and is associated with tolerance to endotoxin-induced ileal mucosal injury and xanthine oxidase activation.

Changes in bacterial composition and enzymatic activity in ileostomy and ileal reservoir during intermittent occlusion: a study using dogs

Bacterial flora, activities of 10 potential mucus- and dietary polysaccharide-degrading enzymes, blood group antigenicity of the intestinal glycoproteins, and proteolytic activity in the output from experimentally colectomized dogs with conventional ileostomies and dogs with valveless ileal reservoirs (pouches) were determined. The ileostomies of dogs with conventional surgery (group II) and with pouches (group III) were occluded intermittently during a 6-week period. The duration of occlusion was progressively increased. Group I, five dogs with conventional ileostomies, served as a control group. After occlusion of the ileal pouch for 7 h, total numbers of bacteria increased threefold, glycosidase activity increased fivefold, and blood group antigenicity of the intestinal glycoproteins, which was high in the output from the nonoccluded pouch, was no longer detectable. Proteolytic activity was not influenced by occlusion of the pouch. Significantly lower numbers of bacteria, only minor glycosidase activity, high blood group antigenicities of the intestinal glycoproteins, and higher proteolytic activity were found in ileostomy effluents from groups I and II. Histopathological examination showed chronic inflammation and changes in crypt-villus ratio in all dogs with ileal reservoirs; the ileal mucosa from the dogs with conventional ileostomies did not show any abnormalities. Consequences of the flora-related enzyme activities for the ileal mucosa are discussed.

Factors affecting in vitro growth of harvested enterocytes

Selective enterocyte transplantation may be an alternative to whole organ transplantation for increasing absorptive capacity. Our aim was to determine the effect of initial cell number and viability, proportion of intact crypts, and basement membrane components (BMC) on the in vitro growth of rabbit enterocytes. Enterocytes were harvested using warm trypsinization from ileal segments in 40 rabbits. Initial cell viability was 92 +/- 4% (mean +/- SD), cell yield was 7.7 +/- 3.6 x 10(6) cells/cm, and there were 0.51 +/- 0.33 crypts/100 cells. Initial cell viability correlated with cell yield (r = -0.508, p < 0.001) and % crypts (r = 0.313, p < 0.05). Cell yield also correlated with % crypts (r = -0.645, p < 0.001). Enterocytes (5 x 10(6)) were incubated in growth media in plain or BMC coated growth culture vessels for 14 days. There was a correlation between both number of cells seeded (r = 0.824, p < 0.001) and cell viability (r = -0.696, p < 0.01) and % growth colonies containing epithelial cells at 14 days. Both total growth colonies (r = -0.565, p < 0.05) and colonies with epithelial cells (r = -0.589, p < 0.05) had a negative correlation with % crypts. Incubating cells in BMC coated vessels (n = 6) resulted in significantly more dispase liberated cells after 14 days than in plain vessels (n = 6) (6.6 +/- 1.1 vs. 3.8 +/- 1.0 x 10(6), p < 0.05) but viability was similar (97 +/- 2% vs. 96 +/- 2%).(ABSTRACT TRUNCATED AT 250 WORDS)

Protein malnutrition alone and in combination with endotoxin impairs systemic and gut-associated immunity

Because protein-malnourished or endotoxemic patients are at an increased risk of developing nosocomial infections, this study was performed to investigate the effects of protein malnutrition and endotoxemia, alone and in combination, on systemic and intestinal immunity. Protein malnutrition was created by feeding the animals a solid diet containing 0.03% protein. Subgroups of these protein-malnourished mice were killed after being challenged with saline or endotoxin on days 0, 7, 14, or 21. At death, the animals were weighed, tissues were harvested for histologic analysis (ileum, mesenteric lymph node [MLN], liver, and spleen), mitogen responsiveness (MLN, Peyer's patches, and spleen), and xanthine oxidase measurements (ileum and cecum). Separate groups were evaluated for survival. Both the saline and endotoxin-challenged mice had lost about 30% of their body weight after 21 days on the low-protein diet. The protein-malnourished mice were more susceptible to endotoxin-induced mortality (70% at 21 days) than the normally nourished mice (0%) (p less than .001). The mitogen responsiveness of the protein-malnourished mice to the T-cell mitogens (PHA and Con-A) progressively decreased the longer the mice were protein malnourished, and this decreased in blastogenic responsiveness was associated with histologic evidence of lymphoid atrophy. In contrast, the blastogenic response to the primarily B-cell mitogen, PWM, was largely preserved. The endotoxin challenge further depressed the immune state of mice tested after 0, 7, or 14 (but not 21) days of protein malnutrition. Thus, both protein malnutrition and endotoxin impaired systemic and gut-associated immune responsiveness to mitogens. However, in the protein-malnourished mice, the degree of immune suppression did not correlate with endotoxin-induced mortality.

Novel beneficial mechanisms of defibrotide, a prostacyclin enhancing agent in splanchnic artery occlusion and reperfusion in rats

To further clarify the protective mechanism(s) of defibrotide in splanchnic artery occlusion (SAO) shock, we observed the effect of defibrotide on polymorphonuclear leukocyte (PMN) accumulation in the intestinal tissue, gastric lysosomal hydrolases and endothelial function of the ischemia-reperfused superior mesenteric artery (SMA). Pentobarbital anesthetized rats were subjected to occlusion of both the celiac and superior mesenteric arteries for 90 min followed by 2 h reperfusion. The rats receiving only the vehicle for defibrotide exhibited a marked increase in intestinal myeloperoxidase (MPO) activity and a significant endothelial dysfunction manifested by the loss of endothelium-dependent vasorelaxation. Only 2 of 6 rats (33%) survived 2 h of reperfusion. In contrast, those rats treated with defibrotide exhibited significantly attenuated PMN accumulation in intestinal tissue, enhanced endothelium-dependent vasorelaxation in SMA rings, prolonged survival time and increased survival rate to 6 of 7 (i.e., 86%). However, addition of defibrotide in vitro had no direct effect on LTB4 activated PMN adherence to vascular endothelium. Moreover, defibrotide preserved gastric lysosomal membranes in vitro. These results indicate that the protective effect of intravenous administration of defibrotide on SAO shock may be related to its endothelial preserving effect reducing PMN adherence and protection of endothelial and lysosomal membrane integrity.

Determinants of regional sucrase-isomaltase expression in adult rat small intestine

Sucrase-isomaltase (SI) expression along the longitudinal and vertical axis of the small intestine was studied by sequentially isolating enterocytes from villus to crypt of rat proximal jejunum and distal ileum. Gradients of sucrase activity were observed with greatest activity occurring in jejunal and villus regions. Along the villus-to-crypt axis, gradients of SI mRNA abundance corresponded with activity. However, along the longitudinal axis no differences in SI mRNA levels were observed, thus not accounting for the observed 3-5-fold difference in SI activities between jejunum and ileum. Comparison of SI immunoprecipitates from jejunal and ileal mucosal scrapings showed significant differences in gel mobilities of the more mature forms, which did not appear to affect SI functional activities. When relative rates of de novo SI protein synthesis were compared, [35S]methionine incorporation into all SI forms was observed to be 3-5-fold greater in jejunum than in ileum at all time points. Because these results suggested differences in regional translational regulation, subcellular distribution of SI mRNA in jejunal and ileal epithelial cells was compared. A greater proportion of jejunal SI mRNA was found to be associated with membrane-bound polyribosomes. We conclude 1) sucrase expression along the villus-to-crypt axis correlates with SI mRNA abundance, 2) post-translational processing of SI differ in ileum and jejunum, but appear not to determine SI expression, and 3) differences in translational processing in distal ileum and proximal jejunum may determine sucrase activity along the longitudinal axis of rat small intestine.

Prostaglandin H synthase immunoreactivity in human gut. An immunohistochemical study

Prostaglandins exhibit a variety of actions on intestinal smooth muscle depending upon the type, dose and muscle layer studied. As the cellular origin of prostaglandin H (PGH) synthase has not been established with certainty in the human gut wall, we studied the localization of PGH synthase in the human duodenum, jejunum, ileum and colon by immunohistochemistry. PGH synthase immunoreactivity appeared to be similar in all segments of the intestine. Most smooth muscle cells seemed to contain PGH synthase; however, the reaction in the lamina muscularis mucosae was much stronger than in the longitudinal and circular muscle layers. Endothelial cells in capillaries and larger vessels showed a positive reaction. In addition, unidentified cells in subserosa, at the level of Auerbach's plexus and in the submucosa were stained. We concluded that the smooth muscle cells of the human gut has a rather large capacity for PGH synthesis and the present results may provide a basis for a better understanding of both normal physiological functions as well as intestinal disease states involving disorders of prostaglandin synthesis.

Glutathione peroxidase and glutathione S-transferase, class alpha, in rat intestine. Immunohistochemical and immunoblotting studies on changes in expression of these antilipoperoxidative enzymes during normal development

Glutathione peroxidase (GSH-PO) and glutathione S-transferase (GST), class alpha, showing GSH-PO-like enzymatic activity, were localized immunohistochemically in frozen sections of rat intestine in order to elucidate changes in the expression of these antilipoperoxidative enzymes during normal development. The direct immunoperoxidase method was performed using specific rabbit antibodies (Fab fragments) against the enzymes purified from rat liver. Immunoreactive GSH-PO and GST-alpha were demonstrated in the intestinal villous epithelial cells. In the duodenum, GSH-PO was positive during the period from 19 days of gestation to 1 week after birth, while GST-alpha was negative during this period. Two weeks after birth, positivity for GST-alpha appeared, and GSH-PO became undetectable. In the ileum, both of the enzymes were observed until 2 weeks of age, but after weaning their expression disappeared. These immunohistochemical findings were confirmed by immunoblot analysis using intestinal tissue extracts. To evaluate environmental effects on the expression of these enzymes, germ-free animals, common bile duct-ligated rats, and Hank's solution-fed infant rats were prepared. No remarkable alterations in the immunohistochemical localization pattern were observed. Since the switching of enzyme expression around the time of weaning was not influenced by these experimentally induced environmental conditions, it appears that these enzymatic changes are genetically predetermined.

Protective actions of a leukotriene B4 antagonist in splanchnic ischemia and reperfusion in rats

Pentobarbital-anesthetized rats were subjected to occlusion of both the celiac and superior mesenteric arteries for 90 min followed by reperfusion for 2 h. All seven rats given only the vehicle died within 2 h of reperfusion, whereas rats treated with LY-255283 (3 or 10 mg/kg iv), a leukotriene B4 (LTB4) receptor antagonist given 10 min before reperfusion, exhibited significantly higher survival rates of 57% (4 out of 7) and 75% (6 out of 8), respectively, 2 h after reperfusion. Rats given 1 mg/kg of LY-255283 showed no significant improvement in survival. Splanchnic artery occlusion (SAO)-shock rats treated with LY-255283 (3 or 10 mg/kg) exhibited significantly attenuated accumulation of plasma free amino-nitrogenous compounds and of a myocardial depressant factor. Treatment with LY-255283 (10 mg/kg) markedly (P less than 0.01) ameliorated the deficits of endothelium-dependent relaxation of isolated superior mesenteric artery (SMA) rings in untreated SAO-shock rats. LY-255283 at 10 mg/kg significantly attenuated the increased myeloperoxidase activity in the intestinal tissue of SAO-shock rats. Moreover, LY-189444, a closely related compound having no LTB4 antagonist activity, did not protect rats in SAO shock, whereas a lipoxygenase inhibitor confirmed protection in SAO shock. These results suggest that LTB4 plays a pivotal role in endothelial dysfunction occurring in SAO-shock rats by chemoattraction and activation of neutrophils on the surface of vascular endothelial cells. Moreover, LY-255283 but not LY-189444 inhibited the adherence of rat neutrophils to isolated SMA endothelium.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of reticular cells in the ileal Peyer's patch of sheep and goats

The ontogeny of reticular cells in the ileal Peyer's patch of sheep from 70 days gestational age was studied by light and electron microscopy and by enzyme histochemistry. Small to medium-sized lymphocytes were seen in the lamina propria at 97 days, when the stroma was essentially still mesenchymal. By 110 days, the stromal cells in the dome/follicle primordia had differentiated into reticular fibroblasts, whose processes and fibers were seen to surround groups of lymphocytes. With advancing age the number and size of primordia increased, and proliferation was obvious among the lymphocytes. Processes of reticular cells increased in number and penetrated between individual lymphocytes of the groups. Coarser desmosome-like contacts were seen between the reticular cells from 115 days onwards. A central light area in the follicle was apparent from 130 days onwards. The fine structure of the stromal cells in this light follicle center developed towards but never became similar to that of follicular dendritic cells in a typical germinal center. The fine interdigitating end branches of the stromal cells were less numerous, and the dense homogeneous material present in between the end branches was not observed in the ileal Peyer's patch follicle. Instead, small particles and vesicles were seen between the various cell types of the light center and were not restricted to the intercellular spaces between the stromal cells. In the dark peripheral zone of the follicle, the stromal cells retained more immature features. The follicle became bordered by a capsule at an early stage. This capsule was formed by multiple layers of flattened fibroblasts separated by small amounts of intercellular material only. The alkaline phosphatase, Mg(2+)-dependent adenosine triphosphatase and 5' nucleotidase reactivities of the follicular dendritic cells in the ileal Peyer's patch were similar to those of early prenatal primary follicles of sheep lymph nodes. This study indicates that the stromal cells of the ileal Peyer's patch are mesenchymal in nature and different from those of germinal centers and the epithelial stromal cells of bursa Fabricii of birds.

Functional specificity of jejunal brush-border pteroylpolyglutamate hydrolase in pig

To determine the functional specificity of intestinal brush-border pteroylpolyglutamate hydrolase (PPH), we compared the regional location of in vivo hydrolysis of pteroyltriglutamate (PteGlu3) with the location of activity and immunoreactivity of the enzyme in the pig. After in vivo incubations, PteGlu3 hydrolytic products were recovered from intestinal segments in the jejunum but not from the ileum. Brush-border PPH activity in fractionated mucosa was 10-fold greater in the jejunum than in the ileum, whereas the activity of intracellular PPH was increased in the distal ileum. Antibodies to purified brush-border PPH identified a major protein band at 120 kDa and a minor protein band at 195 kDa in solubilized jejunal brush border. Immunohistochemistry identified the enzyme only on the brush-border surface of the jejunum, whereas an immunoblot of solubilized brush-border membranes identified brush-border PPH in the jejunum but not in the ileum. The parallel of the regional location of in vivo hydrolysis of PteGlu3 with the location of brush-border PPH activity and immunoreactivity demonstrates the functional specificity of this enzyme in folate digestion.

Chloroform bioactivation by microsomes from colonic and ileal mucosa of rat and man

The cytochrome P-450 system present in colonic and small-intestinal mucosal microsomes from control and beta-naphthoflavone pretreated rats is not able to catalyze the biotransformation of chloroform either oxidatively or reductively. Anoxic incubations of 14CHCl3 with mucosal microsomes obtained from human colon and ileum biopsies resulted in significant levels of covalent binding to lipids but not to protein; no covalent binding was measured after room-air-equilibrated incubations. The bioactivation of CHCl3 by human colonic mucosal microsomes can therefore occur in conditions which may be representative of the physiologically low oxygenation of the outer layers of this tissue. These results support the possibility of an association between colonic cancer and exposure to CHCl3, claimed in some epidemiological studies, but not evident from studies of laboratory animals.

Effect of pancreatic secretions upon ileal disaccharidase activities of neonatal miniature pigs

Mechanisms by which pancreatic secretions influence disaccharidase activities in the distal small intestine have been investigated in 1-week-old miniature pigs. Using a combination of biochemical, cytochemical and morphological techniques it has been found that the decrease in lactase specific activity is due solely to a reduction in villus surface area. By contrast, the increased sucrase-isomaltase activities, which occur despite the reduction in villus surface area, are due entirely to increased enzyme expression during enterocyte differentiation.

Immunohistochemical study on arachidonate 5-lipoxygenase in porcine leukocytes and other tissues

Arachidonate 5-lipoxygenase is an enzyme that catalyzes the oxygenation of arachidonic acid, producing 5-hydroperoxy acid. This enzymatic reaction initiates the biosynthesis of various bioactive leukotrienes. An antiserum was raised in a rabbit against the purified 5-lipoxygenase of porcine leukocytes, and various types of porcine leukocytes were immunostained by use of the antibody. As examined by light and electron microscopy, neutrophils and eosinophils were positively stained. The 5-lipoxygenase was localized in the cytoplasm but not in the plasma membrane and subcellular organelles of the positively stained cells. In contrast, lymphocytes were unstained. In porcine ileum, the majority of 5-lipoxygenase-positive cells were eosinophils and mast cells resident in the lamina propria mucosae, whereas parenchymal cells were not stained. In porcine lung, certain bronchiolar or bronchial epithelial cells were clearly immunostained, in addition to eosinophils and mast cells found in the interstitium.

Food restriction retards age-related biochemical changes in rat small intestine

Previous studies have demonstrated that the specific activities of several proximal small intestinal mucosal enzymes fall in the aging rat. This reduction was due to a delay in the full expression of activity of these enzymes during epithelial cell transit from the crypt onto the intestinal villus. We now show in the ad libitum fed Fischer 344 rat that jejunal sucrase, maltase, and alkaline phosphatase specific activities do not fall gradually throughout the life span, but are reduced during senescence. Caloric restriction to 60% of ad libitum intake (DR) abolishes or delays this fall in enzyme activity. Jejunal mucosal immunoprecipitable sucrase-isomaltase (S-I) content also falls with age, but sucrase specific activity per molecule of S-I is less in the older ad libitum fed (approximately 45) than in the DR rats (approximately 60). Jejunal lactase activity falls gradually throughout the life span of ad libitum and DR rats, but lactase activity consistently was higher in DR animals. These observations indicate that DR alters the age-related changes in the activity of several enzymes in the rapidly replicating gut mucosa.

Interaction of trimebutine and Jo-1196 (fedotozine) with opioid receptors in the canine ileum

Receptor binding of the opioid receptor antagonist, [3H]diprenorphine, which has a similar affinity to the various opioid receptor subtypes, was characterized in subcellular fractions derived from either longitudinal or circular smooth muscle of the canine small intestine with their plexuses (myenteric plexus and deep muscular plexus, respectively) attached. The distribution of opioid binding activity showed a good correlation in the different fractions with the binding of the neuronal marker [3H]saxitoxin but no correlation to the smooth muscle plasma membrane marker 5'-nucleotidase. The saturation data (Kd = 0.12 +/- 0.04 nM and maximum binding = 400 +/- 20 fmol/mg) and the data from kinetic experiments (Kd = 0.08 nmol) in the myenteric plexus were in good agreement with results obtained previously from the circular muscle/deep muscular plexus preparation. Competition experiments using selective drugs for mu [morphiceptin-analog (N-MePhe3-D-Pro4)-morphiceptin] ), delta (D-Pen2,5-enkephalin) and kappa (dynorphin 1-13, U50488-H) ligands showed the existence of all three receptor subtypes. The existence of kappa receptors was confirmed in saturation experiments using [3H] ethylketocycloazocine as labeled ligand. Two putative opioid agonists, with effects on gastrointestinal motility, trimebutine and JO-1196 (fedotozin), were also examined. Trimebutine (Ki = 0.18 microM), Des-Met-trimebutine (Ki = 0.72 microM) and Jo-1196 (Ki = 0.19 microM) displaced specific opiate binding. The relative affinity for the opioid receptor subtypes was mu = 0.44, delta = 0.30 and kappa = 0.26 for trimebutine and mu = 0.25, delta = 0.22 and kappa = 0.52 for Jo-1196. Thus, Jo-1196 had some selectivity for kappa receptors compared to trimebutine. We conclude that there are similar types of opioid receptors in the myenteric plexus and the deep muscular plexus and that specificity of function of opioid nerves must depend on differential location of receptor types on particular neurons. The action of trimebutine and related drugs could vary depending upon their interactions with various gut opioid receptors having different physiological roles.

Ileal compensation for age-dependent loss of jejunal function in rats

Adaptive responses of brush border hydrolases and crypt cell proliferation were measured in the jejunum and ileum of 4-mo-old adult and 28-mo-old senescent male Wistar rats. Responses were measured after rats were deprived of food and then refed with a normoprotein diet (17% protein) or an isoenergetic high protein diet (70% protein). The young rats deprived of food then refed for 18 h with the high protein diet showed better body weight recovery than did old animals. Withholding food for 48 h induced a more pronounced drop of sucrase activity in the intestine of the old rats relative to young rats. Refeeding the high protein diet caused a better recovery of sucrase activity in the jejunum of young rats relative to senescent rats. In the aged animals, sucrase activity in the jejunum remained significantly lower after refeeding both diets. Compared with nourished controls, aged rats showed enzyme activity to be completely restored in the ileum. The high protein diet increased aminopeptidase activity in the jejunum and ileum of young rats, in contrast to the senescent rats in which the increase of enzyme activity was restricted to the ileum. In the jejunum of aged rats, the cell migration rate from crypt base to villus tip was reduced after refeeding, but no age-related changes were observed in the ileum. Our results indicate that the jejunum of senescent rats exhibits reduced adaptive capacities that may be partly compensated by enhanced ileal functions.

Enkephalin-degrading aminopeptidase in the longitudinal muscle layer of guinea pig small intestine: its properties and action on neuropeptides

A membrane-bound enkephalin-degrading aminopeptidase was purified from the longitudinal muscle layer of the guinea pig small intestine by four steps of column chromatography using L-tyrosine beta-naphthylamide. The molecular weight of the enzyme was estimated to be 105,000 by gel filtration. The maximum activity was observed between pH 6.5 and 7.0. The Km value for leucine-enkephalin was 137 microM. The aminopeptidase activity toward aminoacyl beta-naphthylamide substrates was restricted to basic, neutral, and aromatic aminoacyl derivatives. No action was detected on acidic amino acid and proline derivatives. The enzyme was potently inhibited by the aminopeptidase inhibitors actinonin, amastatin, and bestatin, and bioactive peptides such as angiotensin III, substance P, and Met-Lys-bradykinin. The enzyme activity was also inhibited by the antibody against the purified serum enkephalin-degrading aminopeptidase of guinea pig at concentrations similar to those at which activity was observed toward serum enkephalin-degrading aminopeptidase and renal aminopeptidase M. The enzyme rapidly hydrolyzed Leu-enkephalin and Met-enkephalin with the sequential removal of the N-terminal amino acid residues. The enzyme also hydrolyzed two enkephalin derivatives, angiotensin III and neurokinin A. However, neurotensin, substance P, and bradykinin were not cleaved. These properties indicated that the membrane-bound enkephalin-degrading aminopeptidase in the longitudinal muscle layer of the small intestine is similar to the serum enkephalin-degrading aminopeptidase and resembles aminopeptidase M. It is therefore suggested to play an important role in the metabolism of some bioactive peptides including enkephalin in peripheral nervous systems in vivo.