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The study of enzyme activi ty of epi thel tocytes in macrocolon ies of the smal l intest ine developing f rom a single stern cel l has shown the i r s t r i c t ly individual functional differentiat ion, with predominance of one pa r t i cu la r enzyme in mos t colonies [1]. The dimensions of the colonies studied also var ied considerably . It was accordingly suggested that co r re la t ion may exis t between enzyme activity of the epithelium of the m a c r o colonies and the i r s ize . To tes t this hypothesis it was decided to compare the weight of t e s t colonies of epi thel iocytes and the act ivi ty of ce r ta in enzymes concerned with contact digestion of the cel ls of these colonies, in o rde r to identify any possible re la t ionship between the degree of enzyme different iat ion of the rnacrocolonies and the i r s ize .

The effectiveness of different sulfur-containing compounds in supplying inorganic sulfate for sulfate conjugation was studied in isolated cells from rat small intestine, kidney and lung. With cells isolated from the small intestine and kidney, inorganic sulfate was by far the most effective source for intracellular active sulfate as judged by the ability to support sulfate conjugation of 7-hydroxycoumarin. Kidney cells could also use cysteine, N-acetylcysteine and glutathione as a sulfate source, whereas isolated small intestinal cells did not seem to break down and use these sulfur-containing compounds. With isolated lung cells cysteine was the most efficient sulfate precursor. Of the other precursors N-acetylcysteine and inorganic sulfate were used for sulfate conjugation to some extent.

The effects of feeding single doses of β-sitosterol, campesterol and stigmasterol on cholesterol concentration in the rat small intestine was studied to clarify their roles in cholesterol absorption. The different plant sterols affected free and ester cholesterol concentrations differently in the different intestinal segments suggesting that they have different effects on such intestinal processes as uptake, esterification and possibly synthesis of cholesterol and transport of cholesterol esters out of the mucosal cells into the lymphatics.

Chronic administration of alcohol to well-nourished rats led to striking changes in the small intestinal cell population. The present experiments corroborate the view that alcohol is directly toxic to the small intestine.

The carcinogenic potency of methyl methanesulfonate (MMS) and its combination effect with methylazoxymethanol (MAM) acetate were evaluated in rats. MMS was suggested to be weakly carcinogenic for the small intestine. Syncarcinogenic effects of MMS and MAM acetate which could be due to summation of their genotoxic influences were obtained in the small intestine and liver.

Rats fed a zinc-adequate diet exhibited a nonuniform distribution of zinc in the small intestine. The zinc content of zinc-deficient rat small intestine was reduced, particularly in the duodenum and distal ileum. It is possible that the difference in the intestinal zinc content may reflect the rate of zinc absorption in the tissue. Uptake of 65-Zn by intestinal segments in vitro showed that the pattern of absorption obtained is dependent upon the parameters used for quantitation. This observation could account for the variation between the results obtained by different experimental methods of determining the site and rate of absorption of the nutrient.

Folate binding proteins in milk were tested for their effect on folate absorption. The uptake of bound folate by isolated mucosal cells from the rat small intestine was twice that of free folate and differed from it in being more effective with progression down the small intestine, in not being affected by glucose or Dilantin, in having a higher pH optimum, and in being affected by calcium concentration. This milk factor may enhance folate absorption in infants, whose risk of folate deficiency is high.

We have suggested previously that the histamine-diamine oxidase system is involved in cell proliferation. Therefore, the diamine oxidase activity and the histamine content were studied during mucosal proliferation induced by 70% resection of the small intestine of the rat with and without aminoguanidine (AG), a specific inhibitor of diamine oxidase (DAO). The DAO activity underwent a marked alteration during the period of mucosal proliferation, probably as an expression of an antiproliferative regulation mechanism. The histamine content decreased in the proliferating mucosa. No influence of AG on mucosal proliferation could be found, which might be due to a compensatory activity of the interconversion pathway.

We demonstrated the possibility of a successful transplant of foetal rat small intestine into the peritoneal cavity of adult rats. Several combinations of rat strains with defined genetic differences were chosen. On the whole, in more than 66 percent of the performed transplantations a successful adequate growth of the transplants was noted. Oral application of Cyclosporin A (20 mg/kg/d) as immunosuppressive to prevent allograft rejection was necessary only in the combination across major genetic barriers. The preoperative insertion of a 7-0 non-absorbable thread into the lumen of the transplant helped to develop a tubular segment of small intestine which can be anastomosed to the intestinal continuity of the host in a second stage operation.

SummaryUsing an in vivo, acute loop technic it has been shown in the rat that absorptive activity for conjugated cholate increases nearly 4-fold as the small intestine is descended from duodenum to terminal ileum.

SummaryVitamin B12 bound to rat intrinsic factor concentrate was made dialyzable by the supernate of the homogenate of only the proximal 10% of the rat small intestine. Since the major site of absorption of vit. B12 in the rat is the midileum, the present finding throws doubt upon, but does not exclude, the possible physiologic role of such “releasing factor” in absorption of vit. B12 by the rat.

The effects of phenformin on glucose and water absorption from isolated perfused rat small intestine were studied. Luminal phenformin inhibited glocose and water absorption progressively as its concentration was increased from 0-1-1-0 mg.ml-1. At 0-5 mg phenformin ml-1, inhibition increased with time of exposure to phenformin up to 15 min and thereafter remained constant. Arterial infusion of phenformin (1-0 mg-ml-1) produced less inhibition of glucose and water absorption. The site of phenformin's action appeared to be intracellular. Phenformin absorption from a luminal perfusate (0-5 mg-ml-1) was measured. Although it was rapidly absorbed (22 microgram.cm intestine-1.h-1) from the lumen, less than 2 microgram.cm-1.h-1 appeared at the serosal surface of the intestine. In subsequent phenformin-free perfusion, only 25% of the absorbed phenformin was recovered in the luminal and serosal effluents.

The small intestines of adult rats were examined by light and scanning-electron microscopy after sublethal doses of methotrexate were injected at 5, 3 and 1 mg, respectively, per rat per day, for three days. Methotrexate inhibited mitosis and thereby disrupted the steady state system of the epithelium. Villi and crypts progressively diminished up to about four and one-half days after the initial injection. Thereafter, recovery began and, by day 7, relatively normal morphology was restored. In the degenerative phase, the loss of crypt-villus continuum was frequently observed, the former crypts forming cyst-like structures. The columnar cells became flat and pleomorphic but epithelial continuity was maintained. Goblet cells apparently decreased in number. Paneth cells, especially in the ileum, appreciably increased in size and number. During the recovery phase, the cystic crypts apparently re-established continuity with the villus epithelium. Size and proportion of all epithelial cell types returned to normal. Scanning electron microscopy showed villus fusion and the cellular pleo-morphism and loss of microvilli during the degenerative phase. During recovery of the villi some alteration in orientation and shape remained as shown by scanning electron microscopy.

The properties of thiamine diphosphatase (TDPase) and p-nitrophenylphosphatase (p-NPPase) in rat small intestine were investi gated. TDPase activity, like p-NPPase activity, was high in the mucosa and in the proximal region. Both activities were high in the membrane associated fractions of the duodenal mucosa. Furthermore, TDPase had the same properties as intestinal alkaline phosphatase (al-Pase). These results suggest that thiamine diphosphate (TDP) and p-nitrophenyl phosphate (p-NPP) are hydrolyzed by a single enzyme, al-Pase, in the intestine.

Fucosyltransferase activity of rat small intestine microsomes is solubilized by 0.5% Triton X-100. The solubilized activity can be purified up to 8,300-fold using DEAE-cellulose and affinity chromatography on GDP-Sepharose. At this step, chromatography on Sephadex G15 separates different specificities: N-acetylglucosaminide-alpha-(1,3)-fucosyltransferase acting on asialoserotransferrin, and galactoside-alpha-(1,2)-fucosyltransferase acting on O-glycans of asialofetuin. The use of small saccharidic acceptors also indicates the presence of a N-acetylglucosaminide-alpha-(1,4)-fucosyltransferase and of a very weak glucose-alpha-(1,3)-fucosyltransferase activity. These activities are tightly bound to concanavalin A-Sepharose, suggesting that they are supported by N-glycosylproteins.

Research in recent years has shown that under certain conditions digitalis has a strong vasoconstrictive effect in the splanchnic region. This may imply that in cases of mesenteric ischaemia, digitalization may inhibit a collateral circulation necessary for restoration of the intestinal function. In this investigation the effect of digitoxin on the exchange circulation of the small bowel mucosa was studied in rats with induced regional ischaemia of the intestine. On analysis 30 min after establishment of the ischaemia a statistically significant negative effect of digitoxin was observed.

The absorption of inorganic, trivalent chromium (Cr) by the rat small intestine was investigated by quantifying three components of the absorptive process: 1) Cr uptake from a test meal, 2) Cr transport into the circulation and 3) Cr retention by the intestine. An in vitro, in situ double-perfusion technique was used in which the intestinal vasculature, from the superior mesenteric artery to the portal vein, and the intestinal lumen, from the duodenum to the ileum, were perfused simultaneously. The vasculature was perfused with a synthetic "plasma" (vascular perfusate) while the lumen was perfused with a nutrient-rich solution (intestinal perfusate) at concentrations of trivalent Cr of 0.2-20 mumol/l (10-1000 ppb). Dose-response curves, in which Cr transport, retention and uptake were plotted against the luminal Cr concentration, revealed that Cr absorption is a nonsaturable process. Regardless of the Cr concentration of the intestinal perfusate, 5.90 +/- 0.33% (mean +/- SEM) of the test dose was taken up from the meal, 5.52 +/- 0.33% was transported into the vascular perfusate and 0.38 +/- 0.03% was retained by the small intestine. Based on the criterion of saturability, it was concluded that inorganic, trivalent Cr is absorbed by the nonmediated process of passive diffusion in the small intestine of rats fed a Cr-adequate diet (1.44 micrograms Cr/g diet).

A system for quality control of the determination of arylhydrocarbonhydroxylase (benzpyrenhydroxylase), ethoxycoumarin-O-deethylase, NADPH-cytochrom-c-reductase, epoxidehydrase and uridindiphosphoglucouronyltransferase was developed. We used lyophilized and frozen samples of postmitochondrial supernatant of rat and guinea pig small intestinal mucosa, which was prepared using a 1:5 ratio of mucosa to K-phosphate buffer. For NADPH-cytochrome-c-reductase, the microsomal suspension from rat small intestine was used. The samples were stored at -30 degrees C. The coefficient of variation within run was about 5% (15 samples), the coefficient of variation between run (15 days) about 10%. The control specimens were stable for 6 months.

Smooth musculature occurs in hollow organs whose contents have to be transported by rhythmic contractions of the walls.

Publisher Summary There is a growing awareness that the small intestine may be an important site for the metabolism of drugs and other foreign compounds. Because of the lack of adequate methods, however, the quantitative importance of the intestine's role in whole body drug metabolism in vivo has been more difficult to assess. Vascular perfusion techniques are well suited for providing such information. They permit study of the intact organ under nearly normal physiological conditions while allowing access to the lumen, the arterial and venous circulation, and the lymphatic drainage. In one technique, the entire small intestine of a rat can be removed en bloc and vascularly perfused in a recycling system with heparinized or defibrinated blood. A second approach, simpler and more normal physiologically, is the vascular autoperfusion of a segment of the small intestine in situ. In this approach, the arterial, neural, and lymphatic connections of the segment remain intact while the venous effluent is totally collected. The collected blood is replaced by a continuous transfusion, into a saphenous vein, of heparinized blood obtained from other donor rats. With appropriate adaptations, this technique allows for nearly the entire range of experimentation possible with the isolated preparation.

The oxidation of palmityl-coenzyme A and acetate to CO2 by mitochondria isolated from rat small intestine increases 10-fold at the time of weaning (18-21 days of age). Carnitine palmitoyltransferase (EC 2.3.1.21) activity is 2-fold greater in mitochondria of suckling rat intestine compared to postweaned intestine. These data indicate that carnitine palmitoyltransferase does not control the increase in intestinal fatty acid oxidation during weaning. We have previously reported that the estimated intramitochondrial [NADH]/[NAD+] as determined by the ratio of tissue levels of 3-hydroxybutyrate and acetoacetate is fivefold greater in suckling rat intestine compared to postwean animals. High intramitochondrial [NADH]/[NAD+] which is present in suckling rat small intestine is associated with a decrease in citric acid cycle activity and beta oxidation. The addition of acetoacetate causes a decrease in intramitochondrial [NADH]/[NAD+]. The oxidation of acetate and glucose to CO2 by suckling rat intestine mitochondria was stimulated by the addition of 1 mM acetoacetate. These data suggest that the lower rate of fatty acid oxidation by suckling rat small intestine is controlled by elevated intramitochondrial [NADH]/[NAD+].

A recently established epithelioid cell line derived from rat small intestinal crypt cells was tested for the effects on growth of rat serum obtained from normal, vitamin D-deficient and 25-(OH)D 3 repleted animals as compared to the growth curves established with fetal calf serum. The results suggest that there is a heat-labile growth-inhibiting factor(s) present in normal and 25-(OH)D 3 repleted animals which is not present in vitamin D deficient animals.

Leucine absorption across the mechanically obstructed rat intestine was studied by in vivo and in vitro techniques. It varied between the early (after 2 h) and late (after 18 h) phases of the obstruction. During the early phase there was a reduction in mucosal uptake and in net absorption of the amino acid. At 18 h the inhibition in mucosal uptake was more prominent both above and below the occlusion site but net absorption was only reduced below the obstruction and was relatively unaffected above it. Mannitol and nonmediated leucine absorption were also increased above the obstruction. The findings during the late phase suggest the presence of an increase in leucine permeability across the intestine above the occlusion site. The observed normal rate of net leucine absorption across this segment is thought to be due to enhancement in intestinal diffusion which could be masking the depression in mucosal uptake.

Acid lipase was identified in the rat small intestine by using esters of 4-methylumbelliferone as substrates. Maximum activity towards the oleate ester was found at pH 4.0. In adult animals, the activity of acid lipase exhibited both latency and sedimentability, indicating a lyosomal localization. The activity of acid lipase was practically the same along the height of the villus, thus paralleling the distribution of acid beta-galactosidase. In adult rats, the activity of acid lipase in proximal (jejunum) and middle (mid-jejunum) sections of the small intestine was practically the same and exceeded the activity in the distal (ileum) section by a factor of 2. In suckling rats, the activity of the enzyme in the mid-jejunum exceeded that in the jejunum and ileum by 2.5- and 1.5-fold respectively. During postnatal development, the acid lipase activity of the mid-jejunum showed a peak between days 10 and 15, at which time it exceeded the adult mid-jejunum activity by 5–6-fold.

The vasculature of an intestinal villus in the cat consists of one arterial limb and several venous limbs connected hairpin-like. The distance between the arterial and venous limbs (length about 1 mm) amounts to 10–20 μm so that the basic requirements for an extravascular shunt and a counter current exchange (CCE) are fulfilled. Equations are derived which describe the influence of a CCE in the intestinal villi on intestinal absorption and elimination, respectively. A CCE retards the absorption or elimination, diminishes the absorption or elimination rate, and builds up a gradient from tip to base during absorption or basis to tip during elimination. The efficiency of the CCE is increased with decreasing villous blood flow (especially with decreasing linear flow rate) and increasing permeability of the substances. The hitherto published experimental data obtained in the cat correspond with the theoretical predictions. The lack of experimental evidence for CCE in the rabbit and rat small intestine may be due to the different structure of their villous vasculature.

Pylorus and bile-duct restrictions did not prevent the anteriad migration of Hymenolepis diminuta in rat small intestine after food feeding. However, migration was inhibited when the common bile-duct was occluded. The results indicate that pancreatic secretion is the migratory cue for Hymenolepis diminuta in rats.

This study was designed to determine the effect of epidermal growth factor (EGF) in the lumen on the pH of the intestinal surface in the rat jejunum, which is referred to as "microclimate-pH". In the control experiment, a significant pH gradient was observed between the mucosal surface (approximately pH 6.8) and the bulk phase (approximately pH 7.3). The microclimate-pH was decreased by 0.2-0.6 pH units after addition of higher concentrations of EGF (3-100 nM) to the lumen. The microclimate-pH thus decreased recovers to the control value by replacing EGF with TES buffer, suggesting that the EGF effect is reversible. Considering that the Na+-H+ exchanger exists on the luminal membrane of the intestinal cells, the decrease in the microclimate-pH which was induced by EGF added to the luminal side may be due to the activation of Na+-H+ exchanger.

Effects of protein deprivation and excessive administration of L-histidine on the accumulation of L-histidine in rat small intestine in vitro were investigated using tissue strips and rings. Compared with a 20% casein diet, a non-protein diet and a 5% casein + 5% L-histidine diet significantly enhanced the accumulation of L-histidine per unit wet weight of the tissue strips. The amount of endogenous L-histidine in the intestine of the animals fed on the excess L-histidine diet was extremely larger than that of animals fed on 20% casein and non-protein diets. Net accumulation per unit wet weight of the strips, calculated by taking into account the endogenous levels of L-histidine, was still significantly higher for rats fed on non-protein and excess L-histidine diets. However, the accumulations expressed in terms of the whole animal were identical irrespective of the dietary regimens. Also, with the intestinal rings no such significant difference as with the intestinal strips was observed among rats with different dietary regimens. It is speculated that dietary conditions affect intestinal absorption by modifying intestinal thickness rather than by influencing the mucosal function to accumulate amino acid.

The activities of soluble (S-COMT) and membrane-bound (MB-COMT) forms of catechol-O-methyltransferase in different regions of human and rat small intestine were determined. S-COMT was the predominant form both in the mucous membrane and in the muscle layers. The activity of S-COMT was more than twice as high in the mucous membrane as in the muscle layer. The activity of MB-COMT was almost equal in the different regions of the gut as well as in the mucous membrane and muscle layers. However, the ratio of the soluble form to the membrane-bound form was close to one in the human muscle layers of the jejunum and ileum.

Microradiographs were made of the vasculature of the ileum of rats following an injection of micropaque. The radius of vessels entering the mesenteric margin of the rat small intestine decreases significantly during its course toward the antimesenteric margin. The relative lack of vascular supply in the antimesenteric region of bowel was associated with a significant reduction ( P P

The lining of the gastro-intestinal tract is protected by a visco-elastic mucus layer. To understand the functions of this layer its components must be studied. We have prepared mucin molecules from rat small intestine using a procedure that avoids proteolysis, reduction of disulphide bonds and high shear.

The cytosol peptidase activities hydrolyzing glycl-L-leucine and L-leucyl-glycine as well as the activities of the brush border peptidases (oligoaminopeptidase, aminopeptidase A, gamma-glutamyl-transpeptidase, dipeptidyl-aminopeptidase IV, and carboxypeptidase) are present in rat fetuses during the early differentiation of the intestine (17th to 19th days of fetal life); they increase then at a different rate, reaching a maximum at various times, in the second and third wk after birth, and then decrease to the adult values during the first month of postnatal life. Only the oligoaminopeptidase activity increases steadily after birth, reaching maximal activity in the last decade of the first month. In human fetuses aged between 8 and 22 wk, the gamma-glutamyltranspeptidase was the only brush border peptidase found to be higher than in adults and children. On the other hand, the aminopeptidase A is remarkably reduced. The dipeptidylaminopeptidase IV and the carboxypeptidase are already at adult level in the youngest fetuses, and the oligoaminopeptidase increases during the period of fetal life studied; at the end of this period, the enzyme activity does not differ from the values found in children and adults. The small intestine of the term and preterm newborn should, therefore be able, with some possible exceptions, to efficiently digest peptides.

1. Transfer and tissue content of125I-radioactivity was measured after administration of125I-(ipodate-sodium) to everted rat jejunal segments. 2. After having administered 10−5M125I-(ipodatesodium) on both sides of the everted sacs the S/M ratio of the concentration of125I-radioactivity was 1.5 in jejunal segments and 2.3 in ileal segments. The tissue content was nearly equal for both segments. According to the apparent partition coefficient for ipodate-sodium at pH7, the125I-radioactivity is accumulated in the tissue about 10-fold. 3. Lowering of the temperature of the incubation medium from 37°C to 15°C prevents the building up of a concentration gradient between the serosal and the mucosal side on either jejunal and ileal segments whereas the tissue content of125I-radioactivity was nearly unchanged. 4. With increasing concentrations (1.6·10−6–9.6·10−4 M) of125I-(ipodate-sodium) administered on the mucosal side the transfer and the tissue content of125I-radioactivity were decreased. This appears to be a toxic effect since in jejunal segments also the S/M ratio for the concentration of glucose decreases. 5. The analysis of the125I-radioactivity in the serosal fluid of jejunal segments showed that the bulk of the125I-radioactivity was present in the aqueous phase and only 33% as the unchanged ipodate-sodium in the organic phase. 10% of the125I-radioactivity must be attributed to inorganic iodine. The concentration of125I-(ipodate-sodium) administered in the mucosal fluid only was 3.2·10−6 M. At lower temperature (7°C) the bulk of the125I-radioactivity in the serosal fluid was found in the organic phase, i.e. as unchanged ipodate-sodium. 6. After the incubation of the aqueous phase with β-glucuronidase or NaOH about 97% of the125I-radioactivity could be extracted into the organic phase. This means that the bulk of the125I-radioactivity in the aqueous phase is present as a conjugate, e.g. ester glucuronide of the unchanged ipodate. 7. Apparently, the process of the conjugation of ipodate-sodium in the mucosal cells is involved in the transfer of the125I-radioactivity across the mucosal epithelium.

The inducibility of the mucosal drug-metabolizing enzymes of rat small intestine was studied by administering 3-methylcholanthrene either intragastrically or intraperitoneally. The aryl hydrocarbon hydroxylase activity was 4.1 times higher after intragastric than after intraperitoneal administration of methylcholanthrene. The ethoxycoumarin-O-diethylase activity was 11 times and UDP-glucuronosyltransferase (with p-nitrophenol as substrate) activity was 3 times higher after intragastric administration than after intraperitoneal administration. The epoxide hydratase activity was, on the other hand, 38% lower after intragastric administration of 3-methylcholanthrene than after intraperitoneal administration. The results suggest that compounds entering the body intragastrically, e.e. in the diet, might have profound enzyme-specific effects on the intestinal metabolic rates of drugs.

The effects of thermal injury (72 h post-injury), 72 h-partial (20% less food) or full starvation on the regulation of phosphofructokinase in the mucosa of rat small intestine were studied. Thermal injury and 72 h-partial or full starvation decreased the activity ratio ν 0.5 / V , but the ratios obtained for thermally injured or fully starved rats were significantly lower than those of controls or partially starved rats. The susceptibility of phosphofructokinase to ATP inhibition was increased after thermal injury and 72 h-partial or full starvation compared to that of normal controls. However, these changes that occurred in the enzyme activities of the rat small intestine were mainly specific to injury per se but do not exclude the contribution of partial starvation during the same period of time.