Differential influence of butyrate concentration on proximal and distal colonic mucosa in rats born germ-free and associated with a strain of Clostridium paraputrificum.

In vivo influence of butyrate in colonic mucosa was studied using a model of gnotobiotic rats monoassociated with a Clostridium paraputrificum. Rats were fed a diet containing increasing amounts of non-digestible carbohydrates, the fermentation of which led to modulated amounts of butyrate in the large intestine. In the proximal colon, the increase in the butyrate concentration alters crypt depth and the number of mucus-containing cells; the increase in butyrate was highly correlated with the number of neutral-mucin-containing cells. Conversely, in the distal colon, no relation was found between the increase in butyrate concentration and crypt depth or number of mucin-containing cells. In both the proximal and distal colon, the mitotic index remained unchanged. In conclusion, in vivo production of physiological quantities of butyrate had a trophic effect on proximal colonic mucosa, but did not influence the distal epithelium.

Food supplementation with milk fermented by Lactobacillus casei DN-114 001 protects suckling rats from rotavirus-associated diarrhea.

Group A rotavirus is the leading cause of diarrhea among children aged 3-36 mo worldwide. Introducing fermented milk products into the infant diet has been proposed for the prevention or treatment of rotavirus diarrhea. The preventive effect of milk fermented by the Lactobacillus casei strain DN-114 001 was studied in a model of germfree suckling rats supplemented daily from d 2 of life and infected with SA11 rotavirus at d 5 (RF group). One group was supplemented with nonfermented milk (RM) and two uninfected groups (CM and CF) received either nonfermented or fermented milk. Frequency and severity of diarrhea were observed. Rats were killed at various times from 0 to 120 h postinfection (p.i.). Bacteria were measured in the intestine, and rotavirus antigens were detected by ELISA in fecal samples and in different parts of the intestine. Histologic observations were made, including vacuolation, morphology of intestinal villi and number of mucin cells. RM rats had diarrhea for 6 d; compared with the CM group, they had alterations of the intestinal mucosa characterized by cellular vacuolation 48 and 72 h p.i. and a lower number of sulfated mucin cells 72 and 96 h p.i. (P: < 0.05). Early supplementation with fermented milk significantly decreased the clinical signs of diarrhea from 24 to 144 h p.i. (P: < 0.05) and prevented rotavirus infection in all sections of the intestine. Histologic lesions of the small intestine were greatly reduced (P: < 0.05) and the number of mucin cells remained unchanged. The data are discussed with respect to the possibility of reducing rotavirus diarrhea in young children by consumption of fermented milk.

Variations in digestive physiology of rats after short duration flights aboard the US space shuttle.

The purpose of this work was to assess the influence of microgravity on several endogenous and microbial parameters of digestive physiology. On the occasion of two Spacelab Life Sciences missions, SLS-1 (a 9-day space flight) and SLS-2 (a 14-day space flight), Sprague-Dawley rats flown aboard the US space shuttle were compared to age-matched ground-based controls. In both flights, exposure to microgravity modified cecal fermentation: concentration and profile of short-chain fatty acids were altered, whereas urea and ammonia remained unchanged. Only in SLS-1 was there an induction of intestinal glutathione-S-transferase. Additional analyses in SLS-2 showed a decrease of hepatic CYP450 and of colonic goblet cells containing neutral mucin. After a postflight recovery period equal to the mission length, only modifications of the hepatic and intestinal xenobiotic metabolizing enzymes still persisted. These findings should help to predict the alterations of digestive physiology and detoxification potential likely to occur in astronauts. Their possible influence on health is discussed.

Variation of mucin distribution in the rat intestine, caecum and colon: effect of the bacterial flora.

The influence of the intestinal microflora on mucin types was studied in the small intestine, caecum and colon of conventional (CV) rats as compared to germ-free (GF) rats. A colorimetric method was used on purified water-soluble mucin extracted from mucosal scrapings and contents. Variations occurred between the three anatomical sites both in the mucosas and intestinal contents of GF rats. In CV rats, the presence of the bacterial flora led to different effects depending on the intestinal site: in the small intestinal mucosa, neutral and sulphomucins values were higher whereas sialomucin was much lower. Conversely, sialomucin was higher in the caecal and colonic mucosas and contents whereas sulphated mucins were decreased significantly in caecal contents and caecal and colonic mucosas. These variations in the contents may reflect the bacterial mucolytic activity and the effect of bacterial metabolites on the mucosa.

Regional cholesterol synthesis in the intestinal mucosa of the genetically hypercholesterolaemic RICO rat: kinetic study following whole-body gamma-irradiation.

PURPOSE: To investigate regional cholesterol synthesis and kinetics following whole-body gamma-irradiation in the genetically hypercholesterolaemic RICO rat. MATERIALS AND METHODS: Male RICO rats were fed a semi-purified diet for 1 month. At 10 weeks old they were exposed to gamma-irradiation (4 Gy, 1.5 Gy/min) together with controls. At intervals from 1-8 days after irradiation an intraperitoneal administration of [1-14C] acetate was given in order to estimate cholesterogenesis in mucosal cells located at different sites in the small intestine. The protein and DNA contents of the different enterocytes isolated along the crypt/villus axis in four equal parts of the intestine were also determined. RESULTS: A marked decrease of the mean quantities of cholesterol, DNA or protein in mucosa was seen 1 and 2 days after irradiation, showing the loss of 30-40% of the intestinal epithelium. An overshoot of the cell amount was observed after 4 days with a return to basal values by 8 days after irradiation. The kinetic and topological evolution of cholesterol radioactivity, which reflects in situ cholesterol synthesis, showed a typical gradient in controls and at 8 days after irradiation. Cholesterogenesis decreased from the first to the third quarter of the small intestine (duodenum to proximal ileum), and then increased in the fourth quarter (distal ileum). In all segments of the small intestine, cholesterogenesis decreased from crypt cells to villus tip. At days 1 and 2 the gradient of cholesterogenesis on the villus was abolished. A slow recovery was seen from day 4 with a strong overshoot of cholesterol synthesis in crypt cells in every part of the small intestine. CONCLUSIONS: The RICO rat is a useful model for studying the effect of irradiation on regional cholesterogenesis in intestinal mucosa. Cholesterol synthesis in crypt cells was lowered 1 and 2 days after irradiation, over-expressed after 4 days and subsequently returned to its normal level.

Development of a heterologous model in germfree suckling rats for studies of rotavirus diarrhea.

Germfree suckling rats were infected with an SA11 rotavirus strain. Infected pups developed diarrhea associated with histopathological changes. The virus was detected in feces and in the small intestine. Cellular vacuolation was observed in the villi of the jejunum. These results provide a new model for further investigations of group A rotavirus infection.

Selective in vitro degradation of the sialylated fraction of germ-free rat mucins by the caecal flora of the rat.

Mucins, which are synthesized throughout the gastrointestinal tract, may be degraded by the microflora of the large intestine. The present study was undertaken to determine the differential fate of the various types of mucins. Mucins from germ-free rats were incubated in vitro in the presence of whole caecal flora from the conventional rat. Neutral, acidic and acidic sulphated mucins were spectrophotometrically assayed over time upon anaerobic incubation. Sialylated mucins were more rapidly degraded (90%) than the other two types after 1 h and almost completely within 4 h. Neutral and acidic sulphated mucins, with a 10-fold and 30-fold lower content than the sialylated fraction in the original substrate, were more slowly degraded and to a lesser extent within 4 h, (55 and 40%, respectively). The method used in the present study made it possible to investigate the activity of gut bacteria towards the various types of mucins. The degradation of the three mucin types was not uniform, the highest rate and extent of degradation being observed for sialylated mucins.

Colonic mucin discharge by a cholinergic agonist, prostaglandins, and peptide YY in the isolated vascularly perfused rat colon.

UNLABELLED: The model of the isolated, vascularly perfused rat colon was assessed in the present study to investigate the nervous, hormonal, and local/paracrine pathways involved in colonic mucin secretion. A colonic loop was perfused via the superior mesenteric artery with a Krebs-Henseleit buffer containing 25% washed bovine erythrocytes at a rate of 2.5 ml/min. After a 10-min control period, each compound to be tested was infused intra-arterially for 30 min. Tissue samples from the proximal and midsegments of the perfused rat colon were then fixed and stained for mucus cell count. Intra-arterial administration of bethanechol evoked a concentration-dependent decrease in the number of stained mucus cells per crypt section over the range 2 x 10(-6) to 2 x 10(-4) M: 16.6 +/- 1.4 stained mucus cells per crypt in the midportion of the perfused rat colon (n = 5) with bethanechol 2 x 10(-4) M versus 28.8 +/- 1.5 for controls (n = 6). After infusion of 1.25 and 2.5 microM 16,16-dimethyl prostaglandin E2 (dmPGE2), the number of stained mucus cells per crypt section was significantly reduced: 21.6 +/- 0.6 (n = 6) and 20.6 +/- 1.4 (n = 7), respectively. An increase in the number of cavitated mucus cells was also observed (22.1 +/- 6.7 and 38.5 +/- 4.1% of cavitated mucus cells in the midsegment of the perfused rat colon with 1.25 and 2.5 microM dmPGE2, respectively, vs. 12.3 +/- 4.1% for controls). In contrast, prostaglandin F2alpha did not significantly affect mucus discharge from colonic cells. Peptide YY (10(-10), 10(-9) and 10(-8) M) induced a dose-dependent increase in the percentage of cavitated mucus cells (16.7 +/- 2.8, 23.1 +/- 4.2, and 31.2 +/- 3.4% of cavitated mucus cells in the midsegment, respectively). The proximal and midsegments of the perfused rat colon were equally sensitive to each secretagogue. CONCLUSION: In the isolated, vascularly perfused rat colon, mucus cells strongly respond to the well-known mucin secretagogues, bethanechol and dmPGE2. This approach has already led to the identification of a novel stimulant of mucin secretion: peptide YY. Our ex vivo model, in which goblet cells are submitted to well-defined luminal and blood-borne stimuli is, therefore, reliable to investigate the nervous, hormonal, and local/paracrine pathways involved in the colonic mucin secretion.

Intestinal mucin distribution in the germ-free rat and in the heteroxenic rat harbouring a human bacterial flora: effect of inulin in the diet.

A colorimetric method was used on water-soluble mucin extracted from mucosal scrapings and contents of the caecum and the colon of five germ-free (GF) rats and five heteroxenic (HE) rats harbouring a human flora (GF rats associated with a human flora). These rats were fed on a diet containing either 100 g sucrose/kg or 100 g inulin/kg. Histological stains, periodic acid-Schiff, alcian blue pH 2.5 and alcian blue pH 0.5 were used to discriminate between neutral, acidic and acidic sulphated mucins respectively. Spectrocolorimetric assays led to a calculated absorbance value for 1 mg of the initial mucin extract. Each mucin type was compared between treatments. The caecal contents of GF rats contained more acidic mucin than sulphomucin, which was present in the same proportion as neutral mucin. Their colonic contents contained more acidic mucins than sulphomucin, which in turn was more abundant than neutral mucin. Their caecal mucosa mucin distribution differed from that of the contents: very little acidic mucin was present and neutral and sulphomucin proportions were of the same order of magnitude. Inulin increased the amount of neutral mucin in the caecal contents and of sulphated mucins in the colonic contents and increased the amounts of neutral and acidic mucins in the caecal mucosa. Mucin distribution in the HE rats was very different from that in the GF rats: the caecal contents contained a high proportion of acidic mucins and very little sulphomucin. The same distribution of mucins was observed in the colonic contents. The caecal mucosa contained less acidic mucin and more sulphomucin than the caecal contents. Inulin decreased acidic mucins and increased sulphated mucins in the caecal contents and increased neutral and sulphated mucins in the colonic contents. Inulin increased sulphomucin in the caecal mucosa and decreased acidic mucin in the caecal and colonic mucosas. The very low amount of mucin that was recovered in the colonic mucosa suggests that, in the presence of the bacterial flora and associated with inulin in the diet, mucin was extensively released from the mucosa to the colonic lumen. This might be related to the bacterial metabolites produced.

Glucose, galactose, and glutamine metabolism in pig isolated enterocytes during development.

In the pig, the gastrointestinal tract grows rapidly after birth and undergoes a short postnatal maturation. The objective of the present work was to assess the metabolic characteristics of the small intestinal mucosa during this period by investigating glucose, galactose, and glutamine metabolism in pig isolated enterocytes. Piglets were used immediately after birth or at various stages during suckling or postweaning. Fed animals were taken in a postabsorptive state. The jejunoileum was excised and perfused with an EDTA (5 mM)-containing buffer. The epithelial cell layer was further dissociated in the presence of hyaluronidase (0.01%). The resulting cell suspension (95% absorbing enterocytes; viability greater than 90%) was incubated with 14C-labeled substrates to measure 14CO2 production in parallel with substrate disappearance. The capacity to utilize glutamine was high and remained steady during the suckling period. Glucose utilization capacity was limited at birth and increased more than 3-fold during the first week of suckling. Such an increase was not observed in piglets kept unsuckled since birth. Galactose utilization capacity remained steady during the first week but afterward gradually disappeared. Lactate and pyruvate production through glycolysis was the major pathway accounting for glucose or galactose disappearance. A capacity for a net glucose production from galactose was evidenced during the first week of suckling. Thus, isolated newborn pig enterocytes exhibit specific and transient metabolic characteristics during the first postnatal week.

[Selective determination of different types of gastrointestinal mucins:use of histochemical reagents]. / Mise au point d'un dosage sélectif des différents types de mucines gastro-intestinales: utilisation de réactifs histochimiques.

A method, transposed from the mucin histochemical stainings, was proposed to evaluate neutral, acidic and sulphated mucins by spectrocolorimetry. Stainings used were periodic acid/Schiff (PAS), Alcian blue (AB) pH 2.5, and Alcian blue (AB) pH 0.5. Mucin samples were extracted from mucosal scrapings, from intestinal contents of germ-free rats or from commercial pig gastric mucin. A mucin-enriched fraction was obtained and lyophilised and the protein content was determined. Each mucin type was spectrophotometrically analysed after staining and precipitation by slightly modified Carnoy fixative. The histochemical stainings used here, after modification by Carnoy fixative treatment, were, as shown by electrophoretic controls, specific for mucin types contained in these mucins without protein contaminant interference.

Effects of galacto-oligosaccharide and bacterial status on mucin distribution in mucosa and on large intestine fermentation in rats.

The purpose of the present paper was to study the effects of a dietary undigestible carbohydrate and intestinal microflora on mucin distribution (neutral, acid, sulphonated), glycolytic activities: beta-D-galactosidase (EC 3.2.1.23), N-acetyl-beta-D-galactosaminidase (EC 3.2.1.43), N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30), alpha-L-fucosidase (EC 3.2.1.51) and bacterial metabolism (gas production, short-chain fatty acids (SCFA) and lactic acid caecal concentration) in germ-free (GF), conventional (CV) and heteroxenic (HE) rats (GF rats associated with a human flora). Rats were fed on either a control diet or a diet containing 40 g trans-galactosylated oligosaccharide (TOS)/kg. In GF rats fed on the control diet caecal pH was almost neutral and glycolytic activities negligible. The number of mucus-containing cells increased from the caecum to the colon for the three types of mucin. TOS had no effect in the caecum but it modified mucin cell repartition in the colon. In CV and HE rats fed on the control diet caecal pH was similar (6.8), but caecal SCFA and lactic acid concentrations (mumol/g) and gas production (ml/24 h) were higher in CV (70, 5.9 and 2.3 respectively) than in HE rats (32, 4.6 and 0.4 respectively). In CV, as in HE rats, acid-mucin-containing cells increased from the caecum to the colon and glycolytic activities were similar. TOS reduced acid-mucin-containing cells in the caecum of CV rats by twofold but had no effect in either the caecum or the colon of HE rats. TOS strongly increased beta-galactosidase activity and slightly modified the other glycolytic activities. Its effect on bacterial metabolites depended on bacterial status. However, comparison between CV and HE rats showed no evident relationship between the number of mucus-containing cells and measured bacterial metabolites. Differences between CV and HE rats might be due to bacterial microflora specificity. TOS had an intrinsic effect on mucus cell distribution in the colon of GF rats. In CV and HE rats the presence of the flora abolished this effect.

Metabolic characteristics of pig colonocytes after adaptation to a high fiber diet.

The capacities of viable colonic epithelial cells to metabolize glucose, glutamine and n-butyrate were studied in 30-kg pigs adapted to a high fiber (12% sugar beet fiber) or a low fiber diet. Glucose and glutamine were extensively utilized but predominantly not oxidized, whereas n-butyrate oxidation accounted for 45% of n-butyrate metabolism and was not greatly affected by the presence of glucose or glutamine. With both diets, glycolysis was the major pathway accounting for glucose disappearance. There was a sparing effect of n-butyrate on both glycolysis and glucose oxidation. Moreover, the glycolytic capacity was 25% lower in pigs fed the high fiber diet. Data suggest that 6-phosphofructo-1-kinase could be the regulatory step in glycolysis. Nevertheless, its maximum activity was not affected by the diet or by the presence of n-butyrate. Glutamine metabolism was slightly affected by fiber in the diet and by the presence of n-butyrate. In addition to CO2, butyrate was converted into ketone bodies. Glucose and glutamine did not substantially alter n-butyrate metabolism. We conclude that some metabolic features of pig colonocytes, such as the capacity to oxidize n-butyrate, resemble those of rat and human colonocytes. Moreover, some characteristics, such as the glycolytic capacity, can be modulated by the level of fiber in the diet.

Intestinal mucosal morphometry and ileal epithelial renewal in conventional and germ-free rats fed an amylomaize starch diet.

Intestinal mucosal morphometry and ileal epithelial renewal were studied in conventional (CV) and germ-free (GF) rats fed either poorly digestible amylomaize or normal maize starch diets. Intestinal morphometry and position of labelled enterocytes were studied at various times after tritiated thymidine injection. With amylomaize starch diet, no difference was observed in the size of crypts (C), villi (V) and C + V between duodenum and jejunum both in CV and GF rats. In the ileum, however, values were significantly lower than those in the duodenum and jejunum. Furthermore, the presence of the microbial flora led to higher values when compared with GF values. Despite the morphological modifications in the ileum, no significant difference was detected in the labelled cell positions and epithelial renewal time between CV and GF values. This suggests that the resistant part of amylomaize starch was responsible for the modification in mucosal morphometry and the longer ileal epithelium renewal time in CV rats which then becomes similar to that in GF rats.

Changes in small intestinal mucosa morphology and cell renewal in suckling, prolonged-suckling, and weaned lambs.

No information concerning the effect of weaning on intestinal cell proliferation is currently available in large species with early intestinal morphogenesis, a group including most domestic animals and humans. Changes in intestinal morphology and epithelial cell renewal were investigated in 1-, 5-, and 8-wk-old suckling and 8-wk-old weaned lambs after injection of [3H]thymidine. In suckling lambs a gradual increase in crypt depth occurred with age, especially in the proximal intestine, whereas villus height was significantly reduced in the distal regions. At 8 wk of age weaned and prolonged-suckling lambs exhibited no significant differences in crypt depth throughout the intestine and in villus height proximally. However, weaned lambs had shorter villi in the jejunum and ileum. The highest enterocyte migration rates (4.4-9.7 microns/h) were observed in 1-wk-old lambs. In suckling animals, migration rates decreased with age by 60, 51, and 11% in the duodenum, jejunum, and ileum, respectively. Weaned and prolonged-suckling 8-wk-old lambs had a similar rate of enterocyte migration in the ileum. Furthermore, ruminating animals exhibited only slightly higher migration rates in the duodenum and the jejunum (53 and 15%, respectively). In suckling lambs, epithelial cell renewal required 2.1-4.0, 4.5-6.3, and 4.0-5.3 days at 1, 5, and 8 wk of age, respectively, whereas labeled cells reached the tips of the villi within 3.0-3.1 days in weaned animals. These data suggest that the suckling period corresponds to a gradual and important phase of postnatal intestinal adaptation in the sheep, a species with early patterns of intestinal cell replacement.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a low dietary linoleic acid level on intestinal morphology and enterocyte brush border membrane lipid composition.

The influence of low dietary linoleic acid level (an essential fatty acid deficiency) on the intestine mucosal morphology and the purified brush border membrane (BBM) lipid composition was investigated in the rat. Electron micrographs and morphometric measurements showed that villi and crypt sizes as well as the ultrastructure of epithelial cells were altered. Cholesterol (CHOL) and phospholipid (PL) levels, CHOL/PL ratio and PL class distribution were not changed by the low linoleate diet. However, the fatty acid composition of phospholipids was markedly modified in the enterocyte BBM, showing elevated amounts of palmitoleic (16:1n-7), oleic (18:1n-9) and 5,8,11-eicosatrienoic (20:3n-9) acids and, by contrast, depressed linoleic (18:2n-6) and arachidonic (20:4n-6) acid levels. Although the underlying mechanisms remain unknown the results obtained suggest that essential fatty acids (EFA) could be directly involved in the trigger action of the observed alterations, as regards both their dynamic (metabolic) and structural roles.

[Decrease of the intestinal microflora without consequences for the morphometry and topography of the distal ileum in the mouse treated with antibiotics]. / Diminution de la microflore intestinale sans conséquences sur la morphométrie et la topographie de l'iléon distal chez la souris traitée aux antibiotiques.

The aim of this study was to assess the possible modifications in the conventional intestine when deprived of its symbiotic microflora. The experiment was designed to study the effect of a heavy antibiotic dose on fecal microflora during the 33-d treatment period as well as its effects upon the intestinal wall. Conventional adult mice received either a casein-starch diet (conventional controls) or an antibiotic-supplemented (0.66% dry matter, DM) diet (treated conventionals); Furthermore, germ-free (axenic) mice taken from isolators to the open animal room received the same antibiotic-supplemented diet (treated axenics) Fecal microbial population remained around 10(8)/g in the conventional mice while it decreased to 10(3)/g in the treated conventional mice. Fecal microbial population of the treated axenic mice dropped to 10(2)/g. At the end of the 33-d treatment period, no significant difference in ileal villus height between the treated or control groups no difference either was seen in the aspects of the villus and cell surface as shown by scanning electron microscopy. In the control group, however, development of bacterial colonies exhibiting various shapes were observed on the intestinal mucus. Although it was found that antibiotic treatment was followed by significant changes in microbial population and biochemical composition of digestive contents, this study concluded that the structure of the distal ileal epithelium was not impaired.

Histamine and mast cell distribution in the intestinal wall of the germ free and conventional rats. Influence of the mode of sterilization of the diet.

The influence of the mode of sterilization of the diet (gamma-irradiation vs. autoclaving) on the histamine and mast cells distribution in the intestinal mucosa, was studied in germ free (GF) and conventional (CV) rats. Interactions between the diet and the digestive microflora were observed. Histamine concentration and mast cells counts are higher in CV rats small intestine than in GF's. The differences are increased with the irradiated diet. At the opposite in the hindgut, these values are higher in GF than in CV rats, especially in the rats fed the steam sterilized diet. The variations in the wall histamine contents and in the mucosal mast cells counts due to the diet and/or the microflora do not appear to be always correlated.

Evolution of the caecal epithelial barrier during Clostridium difficile infection in the mouse.

The most striking effect of Clostridium difficile infection is its degrading of the intestinal barrier. The aim of this study is to establish whether the cellular or paracellular constituent of the barrier is the initial target of the toxins produced by C difficile. Accordingly, the caecal epithelium of C3H/He mice was challenged under three experimental conditions with the C difficile strain VPI 10463: (1) by in vivo inoculation of axenic mice, (2) by adding the toxins to ligated caeca in vivo, and (3) by adding them to the mucosal side of isolated caeca in Ussing chambers. Under all three conditions, the epithelial barrier was tested in caeca mounted in these chambers. The transepithelial potential difference (PD), electrical conductance (G), and intact and degraded Horseradish peroxidase (HRP) fluxes were used as indexes of permeability. Results were as follows: (1) In axenic mice, C difficile caused severe infection, produced toxins A and B, reduced PD, and enhanced G and intact HRP fluxes without changing degraded HRP fluxes, (2) four hours after the toxins were added to ligated caeca in vivo, PD was relatively unaltered, but G, and intact and degraded HRP fluxes increased, and (3) when toxins were added to caeca during two hours in the Ussing chambers, the only modification observed was an increase in degraded-HRP fluxes. These results indicate that the C difficile toxins gradually cause intestinal lesions. After an apparent resistance, they stimulate the endocytotic process and then increase paracellular permeability and finally cause loss of cell viability.

Epithelial cell migration on small intestinal villi in the neonatal rat. Comparison between [3H] thymidine and cytoplasmic labelling after Pu-citrate ingestion.

This study compares, in 2-d-old rats, the migration rates of epithelial cells on villi of the small intestine, using two labelling methods: a single [3H] thymidine injection; and cytoplasmic labelling by a single ingestion of Pu-citrate. Histoautoradiography showed negligible diffusion of Pu after the initial retention, which was mostly confined to the epithelial cells of the villi. However, after sloughing of labelled cells in the intestinal lumen, Pu was reabsorbed by the distal epithelial cells. In segments in which Pu reabsorption was negligible, the migration rates of Pu- and 3H-labelled cells were very close. These rates, expressed in micrometers, were almost constant along the length of the villus, and the Pu and 3H labelling edges reached the top of the villi in about 5 and 7 d, respectively. Once Pu retention had reached its maximum in 9 equal segments cut along the small intestine, tissue counting showed an exponential Pu release of 30-40%/d from each segment until the end of the experiment at d16. This constant release might reflect a constant cell migration rate during the period from Pu ingestion until d16.