Iron Transport by Rat Small Intestine in Vitro: Effect of Body Iron Status

S ummary . Both mucosal uptake and serosal transfer of iron by everted sacs of rat small intestine were maximal in the duodenum and decreased progressively towards the ileum. Transport of iron against a concentration gradient did not occur in any part of the intestine. When the iron concentration in the bathing medium was varied over the range 10–500 μM a saturable transport process was revealed in the proximal small intestine. In iron-deficient rats mucosal uptake of iron was increased but in iron-loaded rats it remained normal. The results suggest that iron transport across the proximal small intestine of the rat in vitro involves a carrier mechanism which responds adaptively to iron deficiency but not to overload.     

Calcium-binding activity of rat intestinal mucosa after massive small bowel resection.

Male Sprague-Dawley rats underwent resection of 50 cm of either proximal or distal small intestine or sham-operation. 6-7 weeks after operation mucosal calcium-binding activity was measured in segments of duodenum ileum and remaining 'midgut'. Similar measurements were obtained from weight and age-matched unoperated rats. There was no difference in calcium-binding activity between unoperated and sham-operated animals. After proximal resection the binding activity increased significantly in duodenum and midgut but did not change in ileum. After distal resection the binding activity decreased in duodenum but was unchanged in midgut and ileum. These studies show that mucosal calcium-binding activity undergoes changes but alteration of the binding activity in remaining gut varies with the location of the small bowel resection.     

Effects of diabetes and vitamin D-depletion on duodenal and ileal calcium transport in the rat

Summary We compared effects of vitamin D depletion and alloxan-induced diabetes on intestinal calcium transport in growing rats. Transport of⁴⁵Ca was studied using everted sacs of duodenum and ileum. Diabetic rats were compared with matched controls (diabetes studies); vitamin D-depleted animals were compared with depleted animals repleted with vitamin D 48 hrs prior to study (vitamin D studies). Duodenal calcium transport was reduced by half or less in experimental groups (diabetic or vitamin D-depleted rats) when compared with corresponding controls (control rats matched with diabetics or vitamin D-repleted animals matched with depleted animals):a) for serosal-to-mucosal (S/M) concentration ratios; andb) per unit weight of mucosa as net transport into serosal medium or net disappearance from mucosal medium. Based on transport into the serosal medium per unit of mucosa, ileal calcium transport was decreased in the vitamin D-depleted group compared with the vitamin D-repleted group in vitamin D studies. In contrast, in diabetes studies ileal calcium transport into the serosal medium was the same in diabetic and control animals. The finding that diabetes and vitamin D depletion have the same effects on duodenal calcium transport agrees witha) lack of specific, vitamin D-dependent duodenal calcium-binding protein in diabetes, andb) restoration of duodenal calcium transport in diabetics by either 1.25-dihydroxycholecalciferol or 1α-hydroxycholecalciferol. Depression of ileal calcium transport by vitamin D-depletion but not by diabetes shows the specificity of intestinal site with respect to mechanisms and control of calcium transport. Diabetes complements vitamin D depletion as a means for studying intestinal calcium transport. Supported in part by Research Grant 16841 from the National Institute of Arthritis, Metabolic and Digestive Diseases, National Institutes of Health.     

Effect of chyme on mucosal enzyme levels in small intestine of the rat

Partial jejunectomies, gastrojejunostomies (with closed pylorus), and jejunal Thiry-Vella loops were made in order to elucidate the role of chyme in the control of mucosal mass and the activities of alkaline phosphatase, ATPase, and maltase in the small intestine of the rat. After partial jejunectomy, a partially reversible mucosal hyperplasia was seen in the small intestine with the exception of distal ileum. After gastrojejunostomy a similar hyperplasia took place in the jejunum and proximal ileum. In the jejunal Thiry-Vella loops a mucosal atrophy was found in 4 wk. After partial jejunectomy the activity of alkaline phosphatase decreased slowly in 4 wk in the remaining small intestine with the duodenum as an exception. ATPase activity decreased in the duodenum. Maltase activity remained unchanged during 8 postoperative wk. In gastrojejunostomized rats the activity of alkaline phosphatase and ATPase increased slowly during 12 wk in the jejunum aborally from the gastroenterostomy. A slight depression of maltase activity was observed in the operation area and a slight increase of enzyme activity was found in the middle of the small intestine. In jejunal Thiry-Vella loops the activity of alkaline phosphatase decreased, but no change of maltase activity could be observed during 4 wk. Perfusion of a loop with maltose solution did not cause any changes in the activity of alkaline phosphatase or maltase. The results indicate that after a change in chyme passage the adaptation takes place in the small intestine primarily by the change of mucosal mass, and at least some enzyme levels in the mucosal cells are remarkably stable.     

Morphological and functional adaptation of the small intestine after colectomy and ileal pouch-anal anastomosis in rats

BACKGROUND AND AIMS: This study investigated morphological and functional changes in the small bowel after colectomy and ileal pouch-anal anastomosis (IPAA). METHODS AND MATERIALS: In 15 rats electrolyte, glucose, and water absorption was determined by in vivo single-pass perfusion of the proximal and distal small intestine 15 weeks after IPAA. Afterwards the small intestine was resected for morphometric evaluation. Controls were 15 identically treated rats without operation. RESULTS: IPAA led to a significant increase in the small intestinal diameter and a significant increase in villus length and density, which was more apparent in ileum than in jejunum. Therefore the mucosal surface per unit serosa increased significantly by 59% in the jejunum and by 76% in the ileum. In the pouch there was a significant increase in goblet cell density, crypt depth, and diameter of the muscularis which was not detectable in the segments proximal from the pouch. Due to the increase in mucosal surface there was a significant increase in total glucose and electrolyte and sorption in the ileum while absorption rates per unit mucosa were unchanged, with the exception of an increase in mucosal sodium absorption. Jejunal absorption and ileal absorption of water remained unchanged. CONCLUSION: Adaptation of the small intestine after IPAA leads to colonic metaplasia in the pouch and intestinal hyperplasia proximal from the pouch. The loss of colonic absorption is compensated by the increase in ileal mucosal surface with subsequently elevated electrolyte and glucose absorption. Changes in intestinal permeability may be responsible for additional water depletion, which is compensated by the upregulation of enteric water and sodium absorption.     

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.     

Changes in serum and intestinal diamine oxidase (DAO) activity after proximal enterectomy in rats

To determine whether serum and mucosal DAO activity reflects quantitative changes in the small bowel mucosal mass, we have chosen an experimental model of mucosal hyperplasia which is known to occur in the rat after enterectomy. A 50% proximal enterectomy or a single transection was performed in 20 growing rats weighing 145–160 g. Ten days following surgery, we determined mucosal mass parameters (weight, protein, and DNA content), sucrase activity, and DAO activity in the duodenum (segment A), proximal ileum (segment B), and distal ileum (segment C) of the remaining small intestine. Mucosal hyperplasia was demonstrated by the finding that in each segment, mucosal weight, protein, and DNA content per centimeter of gut length were significantly (P<0.01) higher (+38 to+78%) in the resected group than in transected controls. In segments B and C of resected rats, the changes in DAO activity expressed per gram of mucosa paralleled the changes in mucosal mass, the activity being increased by +69% and +49% (P<0.05) compared to the values recorded in transected controls. Expressed per centimeter of gut length, total DAO activity was also enhanced by +141% in segment B (P<0.05 vs controls) and by +87% in segment C(P>0.01 vs controls) of resected rats. In the duodenum, the changes in DAO activity were small (+36%) and not significant. In the ileum (segment C), significant correlations were established between total DAO activity and either mucosal weight (r=0.75,N=20,P<0.01) or mucosal DNA concentration (r=0.78, N=20, P<0.01) per centimeter of gut length, but there was no correlation between DAO activity and sucrase activity. Compared to control rats with transection, proximal enterectomy produced marked changes in the serum activity of DAO. Ten days following surgery, the mean value of serum DAO was fivefold higher (P< it0.005) in the resected group than in the transected group. These data indicate that after jejunectomy (1) the intestinal activity of DAO reflects accurately quantitative changes of the mucosal mass in the remaining ileum but not in the duodenum, and (2) circulating levels of DAO could be used as a marker of ileal mucosal adaptation after proximal enterectomy.     

Distribution of the 10,000 molecular weight calcium binding protein along the small and large intestine of man.

The distribution of the 10,000 molecular weight calcium binding protein along the human small and large intestine was studied using an enzyme linked immunoadsorbent assay. Small intestinal mucosal samples were obtained from the duodenal bulb, the second and third part of the duodenum and at about 50 cm intervals from jejunum and ileum of five whole small intestines of necro-kidney donors. Mucosal samples of caecum, colon ascendens, and transversum were also investigated. The amount of calcium binding protein per milligram of cytosolic protein increased throughout duodenum to reach the maximum in the proximal segment of jejunum and then declined steadily to nearly undetectable levels in ileum. In the colon no 10,000 molecular weight CaBP was detectable. The distribution of CaBP along the small and large intestine of man is thus parallel to the efficiency of the active calcium absorption of human intestine.     

Initiation of anastomotic recurrence of Crohn's disease after ileocolic resection. Onset proximal to the junction and preceded by increased phospholipase A2 activity.

Colono-ileoscopy was performed on 11 patients after ileocolic resection for Crohn's disease, to observe development of recurrent anastomotic inflammation and its relationship to mucosal phospholipase A2 (EC 3.1.1.4) activity. Ileal inflammation appeared soon after surgery in eight cases but in none of nine controls with noninflammatory bowel disease. The ileal inflammation was more severe 1-3 cm above than greater than 5 cm above the ileocolic junction (p less than 0.05), whereas the postanastomotic colonic mucosa remained unchanged. Ileal phospholipase A2 activity in the mucosa was equally raised at the two ileal sites (p less than 0.01 and less than 0.02), irrespective of the presence or absence of inflammation. In colonic postanastomotic mucosa the phospholipase A2 activity was the same as in the controls. Further followup showed preanastomotic ileal inflammation at both investigated levels in all patients with Crohn's disease but still with greater severity close to the mucosal junction (p less than 0.05). The study indicates that recurrent inflammation in Crohn's disease is initiated in the terminal ileum close to the ileocolic junction. Progression of severity is accompanied by greater proximal involvement. The increase in mucosal phospholipase A2 activity, which precedes endoscopically detectable inflammation, implies a role for this enzyme in Crohn's disease.     

Effect of ranitidine on gastric and duodenal mucosal enzyme activities in duodenal ulcer patients

The activities of 11 marker enzymes from the gastric and duodenal mucosa were determined in 19 patients with active duodenal ulcer disease (DU) before therapy, after 4 weeks of therapy with ranitidine, 300 mg/day, and after another 4 weeks without treatment. The activities were measured in homogenized material obtained with forceps through an endoscope. The healing rate at 4 weeks was 68%. In the descending duodenum the activities of the membrane enzymes increased during the treatment period compared with pre-treatment activities. Although not as extensive as in the descending duodenum, an increase of membrane enzyme activities was also noted in the duodenal bulb during treatment. In the gastric mucosa only minor enzymic activity changes were seen. The altered enzyme activities in duodenum and stomach during treatment were independent of ulcer healing, smoking, antacids, and mucosal inflammation. Previously, significant differences in mucosal enzyme activities have been demonstrated between DU patients and controls. During ranitidine treatment the enzyme activities in the duodenal mucosa of the same DU patients tended to normalize, whereas they were mostly unchanged in the gastric mucosa. Four weeks after treatment the mucosal enzyme activities in the duodenum were as before treatment started, without occurrence of ulcer relapse. The altered enzymic activities of the duodenal mucosa in DU patients therefore seem to be largely independent of the presence of active ulcer.     

Distribution of neurotensin-like immunoreactivities in porcine and human gut

The distribution of neurotensin-like immunoreactivity (NTLI) in porcine and human intestine was studied by extraction of mucosal and muscular layers of esophagus, stomach, duodenum, jejunum, ileum, and colon. NTLI was quantitated and characterized by radioimmunoassays and gel filtration chromatography. Porcine tissue was obtained in anesthetized animals (n = 6) and human tissue during surgery (n = 28). Concentrations of NTLI increased gradually from the distal esophagus to the ileum. Highest concentrations were found in 2.0 M acetic acid extracts of proximal ileal mucosa (150 (131-223) and 525 (500-729) pmol/g wet tissue, respectively (medians and interquartile range]. After acid extraction, concentrations of intact NT and COOH-terminal and NH2-terminal NTLI were similar, but in water concentrations of NH2-terminal NTLI were high and intact NT and COOH-terminal NTLI low. The distribution of NTLI was similar in the two species. Gel chromatography of ileal, jejunal, and duodenal mucosa indicated that in these tissues NTLI consisted primarily of intact NT. In antral mucosa COOH-terminal immunoreactivity different from NT was detected. The chemical identity is unknown, but it may represent precursor forms of NT.     

Increase of active transport of conjugated bile salts in streptozotocin-diabetic rat small intestine

Active transport of conjugated bile salts, Na-tauro- and Na-glycocholate and D-galactose, was examined in the small intestine of streptozotocin-diabetic rats by an in-vitro technique.Tissue uptake and mucosal to serosal transport of conjugated bile salts and D-galactose was enhanced in diabetic rat ileum. The minimal transport capacity for conjugated bile salts in the jejunum did not differ between diabetic and control intestine. D-galactose transport and transport of 3-0-methyl-glucose were, however, enhanced in diabetic jejunum as well. Kinetic analysis of the initial uptake rates for conjugated bile salts revealed that the maximal transport capacity (Vmax) was enhanced in diabetic ileum.In accordance with earlier results on the effect of experimental diabetes mellitus on digestive-absorptive functions it is suggested that experimental diabetes mellitus increases the transport capacity of active, Na(+)-dependent intestinal transport processes in general.     

Morphometric and Biomechanical Intestinal Remodeling Induced by Fasting in Rats

The function of the small intestine is mechanical to a large degree. To understand the function it is necessary to know how the mechanical stresses and strains can be computed. Nutrition plays an important role in the maintenance of normal gut structure and function. The small intestine undergoes functional changes when food is withheld. To explore the morphological and biomechanical remodeling during starvation, intestinal segments from the fed and fasted rat duodenum, jejunum, and ileum were investigated. After seven days of fasting the animals lost 22% of the body weight and the intestinal mass per length decreased by nearly 40% in the duodenum. Fasting decreased the plasma levels of glucose, insulin, triglyceride, and cholesterol whereas the level of free fatty acids increased (P < 0.001). Fasting decreased the outer circumferential length, wall thickness, wall area, inner circumferential length, and luminal area at the three locations (P < 0.001). Histological examination showed that the mucosal and the submucosal thickness decreased during fasting (P < 0.001), whereas the muscle layers were unchanged. The residual strain on the mucosal surface was compressive. The serosal residual strain was tensile and increased with the highest values after four days of fasting in the duodenum and jejunum (P < 0.001). Fasting shifted the stress–strain curves to the right in both circumferential and longitudinal directions at the three locations (P < 0.04). In conclusion pronounced biomechanical and structural remodeling occurred in the small intestine during fasting for up to one week. Since the contractile properties depend on the passive properties (according to the well-known Hill's model), it can be predicted that the smooth muscle contractile function will also change.     

Augmentation of mucosal adaptation following massive small-bowel resection by 16,16-dimethyl-prostaglandin E2 in the rat

Survival following massive resection of the small intestine is often possible due to substantial hyperplasia of the mucosal surface in the remaining small intestine. While nutrients provide the major stimulus for hyperplasia in the clinical setting, the availability of drugs to augment this process would have obvious therapeutic implications. We evaluated the ability of 16,16-dimethyl-prostaglandin E2 (PGE2 to augment mucosal hyperplasia following massive small bowel resection in the rat. Three groups of 7 Sprague-Dawley rats, 160 g body weight, were subjected to 70% jejunoileal resection. One group was given 150 micrograms/kg of 16,16-dimethyl-PGE2 intragastrically twice daily, a second group 75 micrograms/kg subcutaneously, and a third group was untreated. After 17 days, segmental evaluation of mucosal mass in the remaining small intestine was determined by measuring mucosal protein, DNA, and disaccharidase levels. A significantly greater increase in mucosal mass was developed in the duodenum proximal to the anastomosis in both treatment groups, but neither the proximal nor distal ileum demonstrated significantly more adaptation. Histological examination in the duodenum confirmed the presence of a greater adaptive response in both the intragastrically and subcutaneously treated animals. 16,16-dimethyl-PGE2 appears to augment mucosal adaptation following massive small bowel resection in the rat, primarily in the very proximal small intestine.     

Age related increase of brush border enzyme activities along the small intestine.

Intestinal morphology and brush border hydrolase activities were determined along the small intestine of young adult (three months, n = 10), mature (12 months, n = 10), and senescent (29 months, n = 15) rats. The intestinal segments of the senescent rats contained higher mucosal mass and protein content (p less than 0.05) compared with the young and mature animals. A significant reduction of villus height and crypt depth (p less than 0.05) was found in the proximal intestine during aging. A 35% increase in villus height (p less than 0.05) without changes in crypt depth, was observed in the distal ileum in senescent rats. The activities of sucrase and isomaltase were significantly increased during aging in the duodenum and jejunum (p less than 0.05). Lactase and aminopeptidase activities which showed only minor changes between young and mature animals were significantly enhanced in senescent animals (p less than 0.05) with aminopeptidase exhibiting a three-fold increase in activity in the proximal ileum. The results when combined with those of previous studies suggest that in the aged animal, the increased level of intestinal hydrolase activities may be the consequence of prolonged cellular maturation along the villi in the proximal intestine, and of adaptation to increased concentrations of intraluminal substrates in the distal intestine.     

Effect of serotonin on water and electrolyte transport in the in vivo rabbit small intestine.

The influence of intravenously administered serotonin on water and electrolyte fluxes in the in vivo rabbit jejunum and ileum was examined. Animals were divided into four groups: (1) those receiving saline intravenously while a glucose-free isotonic saline solution perfused the jejunum and ileum; (2) serotonin given intravenously while glucose-free intestinal perfusate was used as in group 1; (3) intravenous saline given while a 10 mM glucose-isotonic saline solution perfused the jejunum and ileum; and (4) intravenous serotonin given while the intestinal perfusate was as in group 3. Serotonin administration resulted in highly significant net secretion of H2O and sodium in both jejunum and ileum in the groups with a glucose-free perfusate. In jejunum, serotonin evoked net water and sodium secretion, whereas controls absorbed water and sodium. In ileum, serotonin significantly enhanced secretion. The addition of glucose to the perfusate completely abolished the serotonin effect. Unidirectional 22Na flux analysis revealed a marked diminution in both mucosal to serosal and serosal to mucosal fluxes in serotonin-treated animals. The decrease in mucosal to serosal flux was greater than the decrease in serosal to mucosal flux, thus explaining the enhanced net secretion observed with serotonin in the groups receiving glucose-free perfusate. In spite of its pronounced effect on water and electrolyte transport, serotonin failed to produce any detectable histological alterations in small bowel mucosa, either by light or electron microscopy. We postulate that serotonin may be an important mediator of the diarrhea so frequently noted in the carcinoid syndrome by virtue of its effects on small intestinal H2O and electrolyte transport.     

Sugar alcohols enhance calcium transport from rat small and large intestine epithelium in vitro

We compared the effect of a variety of sugar alcohols on calcium absorption from the rat small and large intestine in vitro. An Ussing chamber technique was used to determine the net transport of Ca across the epithelium isolated from the jejunum, ileum, cecum, and colon of rats. The concentration of Ca in the serosal and mucosal Tris buffer solution was 1.25 mM and 10 mM, respectively. The Ca concentration in the serosal medium was determined after incubation for 30 min and the net Ca absorption was evaluated. The addition of 0.1–200 mM erythritol, xylitol, sorbitol, maltitol, palatinit, or lactitol to the mucosal medium affected net Ca absorption in the intestinal preparations. Differences in Ca transport were observed between portions of the intestine, but not between sugar alcohols tested. We concluded that sugar alcohols directly affect the epithelial tissue and promote Ca absorption from the small and large intestine in vitro.     

Cysteamine-induced inhibition of mucosal and pancreatic alkaline secretion in rat duodenum

To determine the effect of cysteamine on the alkaline secretion by the duodenal epithelium, pancreas, and Brunner's glands in relation to the pathogenesis of duodenal ulceration, the alkaline secretion by various types of duodenal loops was comparatively studied. The results obtained were as follows: (1) Cysteamine significantly reduced both mucosal and pancreatobiliary alkaline secretion in the proximal duodenum of rats. (2) The ratio of contribution of pancreatobiliary alkaline secretion to total neutralization of acid in the proximal duodenum was 55.9% under continuous perfusion. (3) There was no significant difference between the amounts of alkali per unit volume of the proximal and distal duodenal loops. (4) The alkaline substance secreted by the proximal duodenal mucosa was confirmed to be the bicarbonate. From these findings, it has been concluded that the impairment of bicarbonate secretion by the mucosal epithelium of proximal duodenum, not by Brunner's glands, plays a causative role in cysteamine-induced duodenal ulceration.     

弓形虫感染鼠小肠IgA分泌细胞数量与IgA水平动态变化

目的动态观察弓形虫速殖子经口感染小鼠诱导IgA分泌细胞(IgASCs)数量和抗体应答水平。方法BALB/c小鼠96只,随机选取12只以PBS灌胃(0.5ml/只),其余小鼠用RH株弓形虫速殖子灌胃(1×104个/只),分别于感染后2、4、6、8、10、12和14d各随机处死12只。免疫组化检测小鼠十二指肠、空肠和回肠黏膜中IgASCs数量,ELISA测定小肠液和血清IgA水平。结果IgASCs分布于小肠黏膜固有层中,不同肠段IgASCs数量的变化规律各异。随感染后时间的推移,十二指肠黏膜IgASCs数量呈上升趋势。感染后2～8d,空肠黏膜的IgASCs数量升高,随后下降,至14d降至感染前水平。回肠黏膜IgASCs数量在感染后2～6d升高,随后下降,12d降至低于感染前水平。感染后小肠液IgA水平持续增高,血清IgA无明显变化。十二指肠、空肠和回肠黏膜的IgASCs数量与小肠液IgA水平的相关性分别为r=0.732(P0.01)、r=0.116(P0.05)和r=-0.429(P0.01)。结论弓形虫速殖子经口感染小鼠可诱导十二指肠IgASCs高水平表达和小肠液IgA水平增高,两者呈正相关。小肠液中高水平的IgA主要由十二指肠黏膜IgASCs分泌。     

Bidirectional transfer and tissue accumulation of folic acid by rat intestine in vitro

The transfer and tissue content of 3H-pteroylmonoglutamate (PteGlu) from the mucosal to the serosal side (Jms, TCm) and in the reverse direction (Jsm, TCs) was studied using the everted sac technique. In the entire intestine, except for the colon, 3H-PteGlu was transferred preferentially into the serosal solution. When 3H-PteGlu was applied to the serosal side the final tissue concentration in either jejunal, duodenal, ileal or colonic segments was not significantly different from each other and about two-fold the serosal concentration. Apparently there exists a specific transfer process from the mucosal to the serosal side in the jejunum. The transfer of 3H-PteGlu shows saturation kinetics (S0.5 = 4.9 X 10(-5) mol/l). At low concentration (2 nmol/l) 3H-PteGlu was accumulated within the mucosal epithelium (tissue/mucosal fluid ratio = 3.8). Transfer and accumulation in the mucosal tissue of 3H-PteGlu apparently need high activation energy as indicated by the temperature dependency of these processes. Finally, transfer and accumulation in the tissue of 3H-PteGlu could be inhibited by salazosulfapyridine and phenobarbital.