The ingestion of proteins and colloidal materials by columnar absorptive cells of the small intestine in suckling rats and mice

Sugar absorption by foetal and neonatal rat intestine in vitro

1. Sugar absorption by foetal and neonatal rat intestine has been examined using an in vitro accumulation technique. 2. The capacity for active sugar absorption is present in the rat intestine by the 17th day of gestation. Considerable variation in uptake occurs during the first month post partum; the greatest uptake place during the first week. 3. The absorption of sugars by the developing gut resembles in several respects that by the mature intestine. However, the adult pattern of functional localization along the intestine is not fully established until after the 3rd week post partum. 4. Kinetic studies indicate that variations with age in the distribution of sugar "carriers' along the intestine, rather than changes in the "carriers' themselves, account for the observed variations in absorption.

Fetal monkey absorption of 55Fe from amniotic fluid

A single dose of 0.5 mCi radioiron (55Fe) was injected directly into the amniotic cavity of each of four pregnant monkeys near term. At 6 or 24 hours after 55Fe adminstration, samples of fetal jejunum, ileum, blood, spleen, liver, lung and fetal membranes were taken for radioautography and scintillation counts. Counts were also made on corresponding maternal tissues. Intestinal radioiron levels and localization indicated that fetuses swallowed and absorbed 55Fe within 6 to 24 hours after injection. Silver grains over the meconium bodies of fetal ileum suggested that intestinal epithelium retained at least some of the absorbed radioiron. However, elevated 55Fe levels in fetal blood and hematopoietic organs indicated that transport of radioiron to the circulation had occurred, presumably through fetal intestine, extraembryonic membranes and/or fetal lungs. Transfer of 55Fe across the placenta from fetus to mother occurred at a slow rate, i.e., samples of maternal organs obtained at 24 hours gave low counts.

The transmission of -125-I-labelled immunoglobulin G by proximal and distal regions of the small intestine of 16-day-old rats

1. Standard doses of -125-I-labelled rat IgG were injected into the intestinal lumen of rats aged 16 days, and their sera were sampled 2 and 3 hr later. High concentration quotients were obtained after injection into the proximal small intestime, whereas very little immunoglobulin was transmitted from doses injected into the terminal 20 cm of the small intestine. 2. The villi of the terminal 18--20 cm of the small intestine of 16-day-old rats, the region from which very little transmission of IgG occurred, were lined by tall columnar absorptive cells with very larg supra-nuclear vacuoles. The extent of the terminal intestine, in which this cell type predominated in the absorptive epithelium, varied with age. The importance of defining the precise location of the region of the intestine under examination is stressed. 3. The experimental results and the histological observations are discussed in relation to (a) the results which have been obtained using PVP, which is unsuitable as an indicator of immunoglobulin transport in the rat and (b) the histological composition of the absorptive epithelium and the maturation changes which affect the epithelium between 18 and 21 days.

Soluble neutral and acid maltases in the suckling-rat intestine. The effect of cortisol and development

The 100000g supernatants from 13-day-old suckling-rat intestinal homogenates contained 43.5% of the total intestinal maltase activity, compared with 7.1% in weaned adult rats aged 40 days. The soluble maltase activity was separated on Sepharose 4B into two quantitatively equal fractions at pH6.0, one containing a maltase with a neutral pH optimum and the other a maltase with an acid pH optimum. The neutral maltase was shown to be a maltase-glucoamylase identical with membrane-bound maltase-glucoamylase in molecular weight, heat-sensitivity, substrate specificity, K(m) for maltose and K(i) for Tris. The soluble enzyme was induced by cortisol, but the ratio of the soluble to bound enzyme fell during induction. Solubility of the neutral maltase was not accounted for by the action of endogenous proteinases under the preparative conditions used. It is postulated that the soluble neutral maltase is a membrane-dissociated form of the bound enzyme and that the relationship between these two forms is modulated by cortisol. The acid maltase generally resembled acid maltase of liver, muscle and kidney. It was shown to be a maltase-glucoamylase with optimal activity at pH3.0, and molecular weight of 136000 by density-gradient centrifugation. At pH3.0 its K(m) for maltose was 1.5mm. It was inhibited by turanose (K(i)=7.5mm) and Tris (K(i)=5.5mm) but not by p-chloromercuribenzoate or EDTA. Some 55% of its activity was destroyed by heating at 50 degrees C for 10min. The acid maltase closely resembled beta-glucuronidase and acid beta-galactosidase in its distribution in the intestine, response to tissue homogenization in various media, and decrease in activity with cortisol treatment and weaning, indicating that it was a typical lysosomal enzyme concentrated in the ileum.

Isolation of microvillus plasma membranes from suckling-rat intestine. The influence of premature induction of digestive enzymes by injection of cortisol acetate

1. Cortisone administration to suckling rats leads prematurely to induction of enzymes of the intestinal microvillus plasma membrane and lengthening of the intestinal microvilli. To investigate the membrane changes that might be involved, a method for the isolation of a fraction enriched with microvillus plasma membrane was developed in suckling rats. Plasma-membrane fractions were compared from 13-day-old control rats and from 13-day-old rats given cortisol acetate by subcutaneous injection for 3 days. 2. After cortisol injection, the activity of maltase, trehalase, sucrase and leucyl beta-naphthylamidase increased markedly, and to the same extent, in intestinal homogenates and plasma-membrane preparations. Purification, and recovery of five marker enzymes with respect to homogenate activity, and recovery of protein, were similar for both membrane preparations, particularly after correction for non-membrane activity, which was high in suckling rats and affected by cortisol. 3. In material released from the plasma membrane by digestion with papain, maltase protein was increased after cortisol injection at least as much as maltase activity. Sucrase activity increased at least 200-fold, and this increase was associated with the appearance of a new sucrase band on polyacrylamide-gel electrophoresis. 4. Sodium dodecyl sulphate electrophoresis of plasma-membrane proteins revealed at least four additional macromolecules after cortisol injection. Concurrently several proteins disappeared from the plasma membrane. The added proteins appeared in the main to be removed from the plasma membrane by papain, whereas the deleted proteins were in the papain-resistant fraction. 5. Enzymic stimulation induced by cortisol acetate in the suckling-rat plasma membrane therefore appears to involve the addition of new proteins, rather than activation of proteins in situ. Deletion of proteins from the membrane during induction of hydrolytic enzymes may reflect other phenomena such as protein reorganization associated with the change in microvillus shape.

The absorption of 125I-labelled immunoglobulin G by different regions of the gut in young rats

1. (125)I-labelled homologous IgG was injected into different regions of the small intestine of rats aged 12, 16, 18, 20 and 22 days. At 12 days the proximal and middle regions of the intestine readily absorbed globulin and transmitted it to the circulation. The distal region of the intestine transmitted little to the circulation at all ages tested.2. The intestine loses its ability to transmit globulin to the circulation in a distal-proximal direction. At 16 and 18 days the ability of the middle region had declined significantly, and this decline continued so that little globulin was transmitted from this region at 20 and 22 days.3. The proximal intestine retained the ability to transmit globulin to the circulation in significant amounts up to 20 days.4. There is a close negative correlation between body weight and total radioactivity of the sera of rats which had received doses of labelled globulin into the proximal and middle regions of the intestine. There was no such correlation after injection into the distal intestine - suggesting a restricted throughput of radioactive material by the absorptive cells of this region.5. These results are discussed in the context of the termination of antibody absorption, and in relation to the results obtained using polyvinyl pyrrolidone.

The effects of cortisone acetate on stomach evacuation and the absorption of 125I-labelled globulins in young rats

1. After short exposure (3-5 hr) to I.P. cortisone acetate (5 mg), the reduced transmission of labelled globulin to the circulation in 14-day-old rats is due to the slow release of the oral dose from the stomach. The ability of the small intestine to absorb and transmit globulin to the circulation is comparable in control and experimental animals.2. About 26 hr after cortisone acetate treatment (5 mg), the greatly reduced absorption of labelled globulin from oral doses administered to rats aged 15 days is due to the combined effects of the slower release of the dose from the stomach and to changes which have occurred in the small intestine.3. About 50 hr after the administration of 5 mg cortisone acetate the effect on the rate of stomach evacuation is minimal in rats aged 16 days. When labelled globulin is introduced directly into the duodenum of these animals virtually no absorption occurs.4. The results obtained from the experiments in which labelled globulin was injected into the duodenum support the contention that the proximal half of the small intestine is an important site for macromolecular transport.

Intestinal transport of antibodies in the newborn rat

Evidence has been reported that the proximal small intestine of the neonatal rat selectively transports antibodies into the circulation. This study describes the morphology of the absorptive epithelial cells in this region of the intestine and their transport of several immunoglobulin tracers: ferritin-conjugated immunoglobulins (IgG-Ft) and antiperoxidase antibodies. Cells exposed to rat IgG-Ft bound the tracer on the membrane of tubular invaginations of the apical cell surface. Tubular and coated vesicles within the cell also contained the tracer, as did the intercellular spaces. Uptake of tracer was highly selective and occurred only with rat or cow IgG-Ft; when cells were exposed to chicken IgG-Ft, ferritin-conjugated bovine serum albumin, or free ferritin, tracer did not enter the cell or appear in the intercellular spaces. Experiments with rat and chicken antiperoxidase showed a similar selective uptake and transport of only the homologous antibody. When cells from the distal small intestine were exposed to the tracers, all tracers were absorbed nonselectively but none were released from the cells. Cells from the proximal small intestine of the 22-day-old rat failed to absorb even rat IgG-Ft. A model is presented for selective antibody transport in proximal cells of the neonatal rat in which antibodies are selectively absorbed at the apical cell surface by pinocytosis within tubular vesicles. The antibodies are then transferred to the intercellular space within coated vesicles. Distal cells function only to digest proteins nonselectively.

The influence of exogenous steroids on macromolecule uptake by the small intestine of the new-born rat

1. Plasma concentrations of cortisol and corticosterone measured by competitive protein binding in rats between 5 and 28 days after birth have been related to the intestinal uptake of [(125)I]polyvinyl pyrrolidone (PVP).2. Plasma cortisol concentration was consistently low throughout the period studied, but there was an increase in plasma corticosterone concentration at the time (18-21 days) when PVP uptake declined to zero (closure).3. Injection of a large dose of cortisone acetate 5 days after birth resulted in precocious closure; PVP uptake declined progressively to zero during the 6 days following the injection. Injection of this steroid at 12 days of age caused closure within 4 days.4. Precocious closure induced by cortisone acetate was closely comparable histologically with natural closure; the decline in PVP uptake was associated with the progressive displacement of vacuolated cells from the villi of the terminal intestine.5. Injection of corticosterone at either 5 or 12 days after birth also reduced PVP uptake. However, the reduction was transient and uptake returned to control levels some days after the injection.6. The temporary reduction in PVP uptake following corticosterone injection was not associated with any change in the histological appearance of the small intestine at the light microscope level.7. The injection of either cortisone acetate or corticosterone was followed by a period of impaired body growth and also a reduction of adrenal weight in animals injected at 12 days but not in animals injected at 5 days.

The effect of adrenalectomy or pharmacological inhibition of adrenocortical function on macromolecule uptake by the new-born rat intestine

1. Bilateral adrenalectomy in 18-day-old rats resulted in an extension by approximately 4 days of the period during which the villous epithelial cells of the small intestine took up polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000.2. The eventual termination of PVP uptake (;closure') closely resembled normal closure in control animals: the time course of the decline in uptake and the histological changes indicated that more mature ;PVP-impermeable' cells progressively ascended the villi.3. Injection of Metopirone was ineffective in animals 10 days after birth, but when injected after day 13 caused closure within 3 days.4. Metopirone injection significantly reduced the plasma concentration of corticosterone and caused a marked rise in the plasma concentration of deoxycorticosterone.5. Aminoglutethimide injection also produced precocious closure and had an effect similar to Metopirone on the plasma concentrations of corticosterone and deoxycorticosterone.6. Injection of Metopirone or aminoglutethimide increased the relative adrenal weight compared with control animals. Aminoglutethimide was more effective and caused approximately a 100% increase in adrenal weight.

Ultrastructural changes suggestive of immune reactions in the jejunal mucosa of coeliac children following gluten challenge

The jejunal mucosa of eight coeliac children on a gluten-free diet and two non-coeliac children was studied by light and electron microscopy two to 98 hours after a single challenge dose of gluten. In all coeliac patients the early cytopathological reactions were principally confined to the structures within the subepithelial connective tissue. Changes were observed in the connective tissue fibrils, the basement membranes of epithelial and endothelial cells, the endothelium of small blood vessels, and the type and degree of inflammatory cell infiltration. The timing of these reactions was compatible with the concept that gluten acts as an antigen and combines with antibody in the form of immune complexes in the connective tissue close to the epithelium and to small blood vessels. These changes appeared to precede epithelial cell damage. No subepithelial tissue changes were seen in the non-coeliac patients after gluten challenge.

The mechanism of intestinal uptake and transcellular transport of IgG in the neonatal rat

The transport of immunoglobulins across the intestinal mucosa of neonatal rats provides an excellent model for the study of transcellular protein transport. The mechanism of intestinal uptake and transcellular transport of plasma proteins has been studied in 12-14-day old rats using intraduodenally administered radioiodinated proteins. Appreciable quantities of rat IgG, mouse IgG, rabbit IgG, and all four subclasses of human IgG were taken up by the intestinal wall (19-54% of administered dose at 4 hr) and transported to the animal (10-35% of administered dose at 4 hr). In contrast there was little or no uptake of human IgM, IgA, and IgE and little or no transport of human IgM, IgA, IgD, IgE, albumin, transferrin, and ceruloplasmin. Both the uptake and transport of labeled IgG were significantly inhibited by unlabeled IgG. Further insight into the transport process was obtained from the observation that an appreciable proportion of the label of IgG in intestinal wall homogenates, but not in plasma or intestinal washings, migrated in a sucrose ultracentrifugation gradient much more rapidly than did the administered 7S molecules. This pattern was not observed with other proteins studied. This apparent binding of labeled IgG was also markedly inhibited by unlabeled IgG. In subcellular fractionation studies of intestinal homogenates the complexed labeled IgG was shown to be associated predominantly with cell membrane rather than cell sap fractions. In addition IgG could be shown to bind to purified enterocyte microvillous membranes in vitro. IT IS CONCLUDED THAT IN THE NEONATAL RAT: (a) the major processes involved in both intestinal uptake and transport of IgG are specific and saturable; (b) intestinal transport is associated with complexing of IgG molecules with membranes, most probably with enterocyte microvillous membranes; and (c) the part of the IgG structure involved in this process is probably similar to that involved in the concentration-catabolism effect but is not identical to that mediating other non-antigen combining functions of IgG. Our data are consistent with the existence of specific receptors for IgG on enterocyte microvillous membranes of the neonatal rat. Such receptors would be necessary for the specific uptake and transport of these molecules.

Protein absorption by the intestine of the fetal rat in utero

Horseradish peroxidase (molecular weight, about 40,000) injected into the amniotic sacs in pregnant rats has been identified ultrastructurally, 6 to 18 hours later, within the fetal intestine in the absorptive cells and the underlying vascular endothelium. This indicates that macromolecular protein within amniotic fluid swallowed by the fetus can be absorbed and transported by fetal intestine, and may indicate that physiological compounds can be transported by this enteric route to contribute to fetal development.

Structural features of the epithelio-mesenchymal interface of rat duodenal mucosa during development

In fetal rats 5-7 days before birth, the duodenal epithelium is separated from mesenchymal cells by a well-defined basal lamina. By 3-4 days before birth, when small rudimentary villi are first seen, direct contact between epithelial and mesenchymal cells occurs by means of epithelial cell cytoplasmic processes which project through gaps in the basal lamina into the lamina propria. At contact sites, the epithelial and mesenchymal cell plasma membranes were less than 100 A apart but membrane fusion was not seen. In number and size these epithelial cell processes increase strikingly during the last 2 days of gestation, and they persist in large numbers until 7-10 days after birth. Thereafter, they decrease gradually in both number and size until 3-4 wk after birth, when the morphology of the epithelio-mesenchymal interface resembles that seen in adult rats, i.e., there are only rare epithelial cell processes which penetrate deeply into the lamina propria. The presence of a large number of epithelio-mesenchymal contact sites during the period of rapid growth and differentiation of duodenal mucosa may reflect epithelio-mesenchymal cell interactions which may facilitate the maturation of the duodenal mucosa.

Cell migration and cortisone induction of sucrase activity in jejunum and ileum

The increase of sucrase activity in homogenates of jejunum and ileum of suckling rats after cortisone administration has been investigated. Serial tissue sections of villi and crypts were also assayed for sucrase activity and these results were compared with the migration of cells labelled with [(3)H]thymidine along the villus. By using a low dose of cortisone (0.5mg/day per 100g body wt.) it was found that the sensitivity of the small intestine producing system to cortisone stimulation increased during the suckling period. On the other hand, 5mg of cortisone/day per 100g body wt. produced practically the same increase of sucrase during the entire suckling period. Sucrase activity in homogenates of the entire small-intestinal wall was first detected 24h after the first injection of cortisone (5mg/day per 100g body weight) to 9-day-old animals and maximum activity both in the jejunum and ileum was reached by 120h. Jejunal activity was greater than ileal activity, but the rate of the increase was similar. The half-time of the increase was 23-27h, whereas enterocytes migrate from the base to the tip of the villi in approximately 72h. Comparison of sucrase activity in serial tissue sections of villi and crypts at various times after cortisone treatment showed that the leading edge of sucrase activity proceeds toward the tip of the villi at the same rate as the advancing edge of newly formed cells. Sucrase activity increased in the newly induced cells as they migrated to the tip of the villi. It was concluded that the increase of sucrase activity in suckling rats after cortisone stimulation is due to at least three factors: (1) increase of activity in newly differentiating cells, (2) increased percentage of villus cells with sucrase activity and (3) continued production or activation of sucrase activity as the cells migrate along the villi.

Vacuolated villous epithelium of the small intestine of young pigs

The villous epithelium of the small intestine from healthy pigs, killed during their first month of life, was examined. There were occasional vacuolated epithelial cells throughout the small intestine in most pigs; however, the occurrence of vacuolated epithelium (vacuolated epithelial cells in a continous layer along at least the distal 10% of all villi on the mesenteric side of a histological section) was related to area in the intestine and age of the pig. Ileal epithelium was vacuolated in nearly all pigs examined during their first 2 weeks of life; however, the frequency of vacuolated ileal epithelium was less in pigs examined during their third and still less in those examined during their fourth week of life. Jejunal epithelium was vacuolated less frequently than ileal epithelium and was not seen in pigs more than 11 days old. Vacuolated duodenal epithelium was not seen. Vacuolated ileal epithelium, in suckling pigs during their second week of life, was morphologically similar to that associated with absorption of colostrum in the neonate and took up bovine colostral whey pinocytotically. In contrast to unvacuolated epithelium, vacuolated epithelium stained supravitally with Evans blue dye given orally. Vacuolated ileal epithelial cells examined by autoradiography after exposure to tritiated thymidine had synthesized DNA more than 3 days previously. These observations were compared with reports that considered vacuolated epithelium, in 2 to 3-week-old pigs, to be pathologic. A hypothesis relating vacuolation to age of ileal cells was proposed.

The transmissions of antibodies across the gut of pouch-young marsupials

The transmission of antibodies across the gut of suckling pouch-young was investigated in three species of marsupials (Setonix brachyurus, Macropus eugenii and Trichosurus vulpecula) from Australia.

Mother Setonix, immunized against Salmonella adelaide flagella and Bacteriophage Φ × 174, transmitted the antibodies in milk to their young. In sucrose density gradient runs, the antibody activity in milk whey and in serum of pouch-young, of Setonix and Macropus was found to be in the 7S region only; antibody in the 11S and 19S regions was not detected. Chromatographic preparations of IgM antibodies were fed to pouch-young Setonix which were later bled and their serum titrated for anti-S. adelaide agglutinins and antiphage Φ × 174 activity. The IgM antibodies were not transmitted across the gut in detectable amounts.

Antibodies were present in the blood of pouch-young Setonix within 15–60 minutes of gavage (feeding by stomach tube) of immune serum. In Setonix the capacity to absorb antibodies in the intestine was lost at an age between 170 and 200 days and in Trichosurus it was lost at an age between 98 and 145 days. At these ages the pouch-young were able to leave the marsupium for varying lengths of time. Antibodies did not traverse the rumen wall in a young Setonix whose rumen was isolated from the intestine with ligatures before immune serum was gavaged.

Factors influencing the uptake of [ 125 I]polyvinyl pyrrolidone by the intestine of the young rat

1. The uptake of orally administered [(125)I]polyvinyl pyrrolidone (PVP) of mean mol. wt. 160,000 (K. 60) by the small intestine of young rats was determined 4 hr after feeding by measurement of the radioactivity remaining in the wall after flushing out the intestinal contents.2. PVP uptake was proportional to the administered dose of PVP for doses of 1 mg and below. At higher doses, uptake was no longer in linear proportion, suggesting a degree of saturation of uptake.3. Litters were reared in one of three environmental temperatures: 13, 20 and 30 degrees C, and were tested to determine the age at which PVP uptake ceased (;closure'). The results were evaluated statistically (see Appendix).4. There was no significant difference between the time of closure in animals reared at 20 and 30 degrees C, but, relative to these groups, closure was significantly delayed, by approximately 48 hr, in animals reared at 13 degrees C.5. Once closure had begun, there were no significant differences in the rate of decline in PVP uptake with age between animals reared at different environmental temperatures.6. Separation of the young rats from their mother both before and after the test-feed of PVP caused a considerable reduction in PVP uptake. Provided that the body temperature of the young rats was maintained, the main factor contributing to the reduction in PVP uptake appeared to be the absence of milk, rather than separation from the mother.

Structural changes and the uptake of polyvinyl pyrrolidone in the small intestine of the young goat

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