Specific Inhibition of Cell Proliferation In the Mouse Intestine By an Aqueous Extract of Rabbit Colon

Aqueous extracts from rabbit colon, kidney, testis and small intestinal mucosa were prepared by homogenization and centrifugation at 105,000 g. After precipitation with ammonium sulphate. the 0–50 fraction (F₁) and the supernatant (F₂) were collected, dialysed against a phosphate buffer and tested on mice in vivo. 1 hr after a single injection of F₁ (15 mg content) from colon, the uptake of tritiated thymidine was decreased in jejunal and colonic DNA in mice. This effect, maximal after 3 hr and totally reversible after 7 hr, was found in neither the kidney nor the testis. the F₁ fractions of non-digestive organs (kidney, testis) were also found to exert a significant inhibition on thymidine incorporation into intestinal DNA in vivo. F₁ fractions of intestinal contents, prepared under the same conditions, exerted no significant effects on DNA synthesis in mouse intestine. Conversely, the colon F₂ fraction did not inhibit the synthesis of jejunal and colonic DNA in vivo. A slowing of cellular migration was also noticed in the jejunum and colon of mice injected with colon or small intestine F₁, as ascertained radioautographically by determining the position of the leading edge of the labelled cells in jejunal or colonic F₁-injected mice. Our results suggest that the F₁ fraction of the aqueous extract of rabbit colon contains one or more substances, which may act either on intestinal DNA synthesis or on the G₁-S transition of the cellular cycle in the mouse intestine. This reversible and tissue-specific intestinal action appears to inhibit cell proliferation and presents several of the characteristics defining a chalone, as does the action of small intestinal F₁ previously reported (Sassier & Bergeron, 1977). However, because of a relative lack of origin specificity of this effect, the physiological significance of our data remains to be ascertained.     

EXISTENCE OF AN ENDOGENOUS INHIBITOR OF DNA SYNTHESIS IN RABBIT SMALL INTESTINE SPECIFICALLY EFFECTIVE ON CELL PROLIFERATION IN ADULT MOUSE INTESTINE

Aqueous extracts from rabbit organs were prepared by homogenization and centrifugation at 105,000 g . After precipitation with ammonium sulphate, the 0–50 fraction was separated by ultrafiltration through Amicon XM 100 and XM 300 membranes yielding two filtrate fractions (U₁ and U₂) and one retentate fraction (U₃). Only U₁ and U₃ inhibited thymidine incorporation into DNA. After a single injection of U₁ from rabbit small intestine, the uptake of tritiated thymidine was decreased in mouse jejunal and colonic DNA. This effect, totally reversible after 7 hr, was found in neither the kidney nor the testis. The U₁ fractions of colon and non-digestive organs (kidney, testis) were found not to exert a significant inhibition on thymidine incorporation into intestinal DNA in vivo. The U₃ fraction from rabbit small intestine also decreased the uptake of tritiated thymidine in mouse jejunal and colonic DNA in vivo. However, this inhibition was irreversible and not tissue-specific. Slowing of cell migration was also noticed in the jejunum of mice injected with U₁ or U₃, as ascertained radioautographically by determining the position of the leading edge of the labelled cells in U₁- or U₃-injected mice compared with controls. A decrease of mitotic activity in U₁- and U₃-injected mice was recorded 8·5 hr after a single injection of small intestinal fractions. Our results suggest that U₁ and U₃ from rabbit small intestine contain one or more substances which may act on the G₁—S transition of the cell cycle in the mouse intestine. However, only the effect of U₁ is reversible and tissue specific. Our data suggest the existence of a factor, having a low molecular weight, which regulates intestinal cell proliferation.     

THE EFFECT OF INTESTINAL RESECTION ON THIRY-VELLA FISTULAE OF JEJUNAL AND ILEAL ORIGIN IN THE RAT: EVIDENCE FOR A SYSTEMIC CONTROL MECHANISM OF CELL RENEWAL

Local and systemic control mechanisms have been postulated to explain the maintenance of steady state cell renewal in intestinal epithelium. Permanent alterations of cell renewal resulting in a new steady state imply alterations in control. Intestinal resection appears to cause such alterations resulting in hyper-plasia of the residual intestine. To test the hypothesis of a systemic control, the effect of 60% mid-intestinal resection on Thiry-Vella fistulae of both jejunal and ileal origin was observed in rats. Results showed that hypoplasia occurred in fistulae without resection of the remaining intestine in continuity. Cell counts of crypt and villus columns and tritiated thymidine uptake in isolated whole crypts were reduced. Scanning electron microscopy showed marked hypoplastic alterations in villi. However, when 60% of the intestine in continuity was resected, hyperplasia occurred not only in the residual intestine but in the fistulae of both jejunal and ileal origin. Cell counts of villus and crypt columns were increased along with increased tritiated thymidine uptake per crypt. Neutral cc-glucosidase and non-specific esterase activities did not change as a result of resection but the activities of both enzymes were greater in ileal fistulae than in ileum in situ. Observations on the different resection response of the jejunal versus ileal fistulae lead to a distinction between inherent and induced differences within the small intestine. This study suggests a systemic control of cell renewal. A possible mechanism involving intestinal vascular physiology is discussed.     

EFFECT OF AN INHIBITING FACTOR ISOLATED FROM RAT LIVER ON DNA POLYMERASES IN REGENERATING RAT LIVER

We partially purified an inhibitory factor (LIF), isolated from 105,000 g supernatant of a saline adult rat liver homogenate. LIF stopped in vitro cell multiplication by blocking the G₁—S transition, and reduced in vivo [³H]thymidine incorporation into liver DNA in two-thirds hepatectomized rats. This reduction in DNA synthesis was observed at 24 hr after hepatectomy, even when the LIF was injected before the beginning of the S phase, 10 hr after hepatectomy, i.e. when DNA polymerase activity had not yet increased. Under these experimental conditions, LIF in vivo treatment prevented α DNA polymerase activity from increasing after partial hepatectomy, so that enzyme activity at 24 hr in LIF-treated rats decreased compared to the controls. No direct inhibitory effect of LIF on α DNA polymerase was detected. LIF did not affect β DNA polymerase. These results suggest that LIF plays a part in controlling liver growth.     

ANALYSIS OF THE PROLIFERATION KINETICS OF BURKITT'S LYMPHOMA CELLS

The in vitro proliferation kinetics of a cell line derived from a patient with American Burkitt's lymphoma were investigated at three different growth phases: lag (day 1), exponential (day 3) and plateau (day 5). The growth curve, labeling and mitotic indices, percentage labeled mitosis (PLM) curves and DNA content distributions were determined. The data obtained have been analysed by the previously developed discrete-time kinetic (DTK) model by which a time course of DNA distributions during a 10-day growth period was characterized in terms of other cell kinetic parameters. The mean cell cycle times, initially estimated from PLM curves on days 1, 3 and 5, were further analysed by the DTK model of DNA distributions and subsequently the mean cell cycle times with respect to DNA distributions during the entire growth period were determined. The doubling times were 39·6, 31·2 and 67·2 hr, respectively, at days 1, 3 and 5. The mean cell cycle time increased from 23·0 to 37·7 hr from day 3 to day 5 mainly due to an elongation of the G₁ and G₂ phases. A slight increase in the cell loss rate from 0·0077 to 0·0081 fraction/hr was accompanied by a decrease in the cell production rate from 0·0299 to 0·0184 fraction/hr. This calculated cell loss rate correlated significantly with the number of dead cells determined by trypan blue exclusion. Analysis of the number of dead cells in relation to the cell cycle stage revealed that a majority of cell death occurred in G₁ (r= 0·908; P < 0·0001). There was a good correlation between the in vitro proliferation kinetics at plateau phase of this Burkitt's lymphoma derived cell line and the in vivo proliferation kinetics of African Burkitt's lymphoma (Iversen et al., 1974), suggesting the potential utility of information obtained by in vitro kinetic studies.     

COMPARATIVE PROLIFERATIVE KINETICS OF CELLS FROM NORMAL HUMAN EPIDERMIS AND BENIGN EPIDERMAL HYPERPLASIA (PSORIASIS) IN VITRO

Proliferation kinetics of epidermal cells from normal human skin and lesions of psoriasis (benign epidermal hyperplasia) were studied in vitro. Epithelial out-growths were obtained from skin explants and the cell cycle studied using the conventional method of following two successive curves of labeled mitoses after an initial pulse with ³H thymidine. The length of T_c was 59 hr and 53.5 hr respectively for normal and psoriatic cells. The shorter T_c for psoriasis was due to a shorter duration of S. The growth fraction was 66% and 74% for normal and psoriatic cells respectively as determined by continuous labeling with ³H thymidine. Under the conditions of the present experiments, therefore, normal and psoriatic epidermal cells showed no significant difference in proliferative capacity.     

DNA synthesis in developing two-cell mouse embryos

Mated CF1 (Carworth) female mice were sacrificed at 2 hr intervals between 29 and 43 hr after human chorionic gonadotrophin (HCG) administration. One- and two-cell eggs were incubated in [³H]thymidine for 1 hr. Labeled two-cell embryos were first observed at 31 hr and reached a maximum number at 35 hr. The S period is approximately 6 hr in duration. Although both blastomeres were labeled in most cases, embryos with only one labeled blastomere were more numerous at later times. In vitro labeling was corroborated by injecting [³H]thymidine directly into the isthmic portion of the oviduct. Embryos usually complete the second cleavage division 18–20 hr after onset of DNA synthesis. The cell cycle at the two-cell stage is thus characterized by a G₁ of close to 1 hr, a 6 hr S, and a G₂ of about 12 hr.Embryos developing in vitro frequently fail to progress beyond the two-cell stage. The block is not due to absence of DNA synthesis since these embryos were found to incorporate [³H]thymidine.     

Synchronization of the Human Promyelocytic Cell Line HL 60 By Thymidine

Cultures of the promyelocytic cell line HL 60 were synchronized with thymidine. A concentration of 0.05 mM thymidine and an exposure time of 24 hr was found optimal for blocking about 90% of the cells in S phase. Following release from the thymidine block the cell cultures were followed intermittently over 40 hr for fluctuation in cell numbers, labelling with radioactive thymidine and nuclear DNA distributions. Mathematical evaluation of the results revealed a cycling time of 18.6 hr and a duration of specific cell phases of 8.6 hr, 7.1 hr and 2.9 hr for G₁, S and G₂+ M, respectively. the doubling time was 26 hr and the growth fraction was estimated as 1.     

THE EFFECT OF CYTOSINE ARABINOSIDE IN VITRO ON AGAR COLONY FORMING CELLS AND SPLEEN COLONY FORMING CELLS OF C57BL MOUSE BONE MARROW

This study reports the effect of cytosine arabinoside in culture on two classes of bone marrow progenitor cells in C57BL mice, agar colony forming cells (ACU) and spleen colony forming cells (CFU). Both normal cells and rapidly proliferating cells were studied. The results show that in normal mice, 23 % of ACU but only 7 % of CFU are killed following 1 hr incubation with the drug. With longer periods of incubation, the survival of ACU in the controls is poor, and the results for the drug-treated cultures suggest that the cells are held up in cycle. In continuously irradiated mice, the proportion of ACU and CFU killed after 1 hr incubation with drug is increased to 43–54%, confirming previous results that these cells are proliferating more rapidly than in normal mice. In mice treated with myerlan, 54 % of ACU are killed by 1 hr in vitro exposure to cytosine arabinoside, again confirming that ACU are rapidly proliferating. However, the proportion of CFU killed is lower (23 %). These results are compared with other studies of the effect of cytosine arabinoside in vivo and also with thymidine suicide in the same strain of mice. The results show that cytosine arabinoside has the same effect as tritiated thymidine, and also that the proportion of CFU killed by these agents in vitro is lower than when the agents are injected in vivo. It is suggested that the conditions in culture have an adverse effect on CFU, which cease DNA synthesis, and are protected from the killing effect of cytosine arabinoside and tritiated thymidine. Since cytosine arabinoside in vitro has an effect similar to tritiated thymidine in vitro on bone marrow progenitor cells in C57BL mice, in vitro incubation with cytosine arabinoside could be an alternative method to thymidine suicide for measuring differences in cell proliferation rate.     

THE ABSORPTION OF FAT BY INTESTINE OF GOLDEN HAMSTER IN VITRO

Everted sacs of intestine from golden hamsters were incubated at 37°C for at least 1 hour in vitro with emulsified lipid after removal of both pancreatic lipase and bile salts. The fine structure of intestinal epithelium is well preserved under these conditions. Absorption of fat by the intestinal mucosa in vitro closely resembles lipid absorption in vivo, as observed by both light and electron microscopy. The physiological significance of these observations is discussed. Tubular elements of the agranular endoplasmic reticulum are often strikingly abundant in the apical cytoplasm of intestinal absorptive cells. These have a role in the intracellular transport of fat since they frequently contain droplets of lipid derived from the incubation medium. The rate of fat accumulation in the epithelium appears to be proportional to the concentration in the medium.     

STUDIES ON THE POPULATION KINETICS OF THE WALKER CARCINOMA BY AUTORADIOGRAPHY AND PULSE CYTOPHOTOMETRY

The proliferation parameters of the Walker carcinoma were estimated from both in vivo and in vitro measurements. The transplantable Walker carcinoma 256 was grown in male inbred BD1 rats. During exponential growth, 5-6 days after transplantation, a PLM curve was performed, yielding estimates of Tc ? 18.0 hr, Ts ? 6.4 hr, T_G2+M? 4.1 hr. With the double labelling technique in vitro under 2.2 atm oxygen we obtained: Tc ? 18.2hr, Ts ? 8.2 hr, T_G2+M? 2.0hr. From pulse cyto-photometry DNA content histograms the fractions of cells in the cell cycle phases were calculated using a computer program: f_G1? (47.6 ± 1.1)%, f_s? (34.1 ± 1.0)%, f_G2+M? (18.3 ± 1.5)%. These fractions remained constant between the fifth and the twelfth day after transplantation. At that time the tumour growth had already slowed down appreciably. The growth fraction determined by repetitive labelling was 0.96 on the fifth and 0.93 on the seventh and eleventh day. The cell loss factor was φ? 17% during exponential tumor growth and increased to about 100% between the tenth and twelfth day. The agreement of the cell kinetic data determined by autoradiography from solid tumours in vivo (PLM, continuous labelling) and autoradiography as well as pulse cytophotometry from in vitro experiments (excised material) was satisfactory.     

A COMPARATIVE STUDY OF THE ULTRASTRUCTURE OF MICROVILLI IN THE EPITHELIUM OF SMALL AND LARGE INTESTINE OF MICE

A comparative analysis of the fine structure of the microvilli on jejunal and colonic epithelial cells of the mouse intestine has been made. The microvilli in these two locations demonstrate a remarkably similar fine structure with respect to the thickness of the plasma membrane, the extent of the filament-free zone, and the characteristics of the microfilaments situated within the microvillous core. Some of the core microfilaments appear to continue across the plasma membrane limiting the tip of the microvillus. The main difference between the microvilli of small intestine and colon is in the extent and organization of the surface coat. In the small intestine, in addition to the commonly observed thin surface "fuzz," occasional areas of the jejunal villus show a more conspicuous surface coat covering the tips of the microvilli. Evidence has been put forward which indicates that the surface coat is an integral part of the epithelial cells. In contrast to the jejunal epithelium, the colonic epithelium is endowed with a thicker surface coat. Variations in the organization of the surface coat at different levels of the colonic crypts have also been noted. The functional significance of these variations in the surface coat is discussed.     

Physiological Concentration of Exogenous Lactate Reduces Antimycin A Triggered Oxidative Stress in Intestinal Epithelial Cell Line IPEC-1 and IPEC-J2 In Vitro

Weaning triggers an adaptation of the gut function including luminal lactate generation by lactobacilli, depending on gastrointestinal site. We hypothesized that both lactobacilli and lactate influence porcine intestinal epithelial cells. In vivo experiments showed that concentration of lactate was significantly higher in gastric, duodenal and jejunal chyme of suckling piglets compared to their weaned counterparts. In an in vitro study we investigated the impact of physiological lactate concentration as derived from the in vivo study on the porcine intestinal epithelial cells IPEC-1 and IPEC-J2. We detected direct adherence of lactobacilli on the apical epithelial surface and a modulated F-actin structure. Application of lactobacilli culture supernatant alone or lactate (25 mM) at low pH (pH 4) changed the F-actin structure in a similar manner. Treatment of IPEC cultures with lactate at near neutral pH resulted in a significantly reduced superoxide-generation in Antimycin A-challenged cells. This protective effect was nearly completely reversed by inhibition of cellular lactate uptake via monocarboxylate transporter. Lactate treatment enhanced NADH autofluorescence ratio (F_cytosol/F_nucleus) in non-challenged cells, indicating an increased availability of reduced nucleotides, but did not change the overall ATP content of the cells. Lactobacilli-derived physiological lactate concentration in intestine is relevant for alleviation of redox stress in intestinal epithelial cells.     

LIMITATIONS IN THE USE OF [3H]THYMIDINE INCORPORATION INTO DNA AS AN INDICATOR OF EPIDERMAL KERATINOCYTE PROLIFERATION IN VITRO

The validity of using the incorporation of [³H]thymidine into DNA as an indicator of epidermal keratinocyte proliferation in vitro has been investigated. Other parameters of cell proliferation, direct count of cell number and measurement of DNA content, consistently fail to correlate with changes in [³H]thymidine incorporation into DNA in primary and first passage cultures of rabbit and human epidermal keratinocytes. Maximum incorporation of [³H]thymidine precedes the active growth period by three days. Incorporation declines markedly during the proliferative period. Thymidine kinase activity decreases during the proliferative growth phase. Incorporation of another pyrimidine nucleotide precursor, [¹⁴C]aspartic acid, suggests that in epidermal keratinocytes in vitro the extent of utilization of the salvage and the de novo pathways may be inversely related. In such cases [³H]thymidine incorporation into TCA precipitable material fails to reflect accurately cell proliferation.     

The effect of gastric inhibitory polypeptide on intestinal glucose absorption and intestinal motility in mice

Gastric inhibitory polypeptide (GIP) is released from the small intestine upon meal ingestion and increases insulin secretion from pancreatic β cells. Although the GIP receptor is known to be expressed in small intestine, the effects of GIP in small intestine are not fully understood. This study was designed to clarify the effect of GIP on intestinal glucose absorption and intestinal motility. Intestinal glucose absorption in vivo was measured by single-pass perfusion method. Incorporation of [¹⁴C]-glucose into everted jejunal rings in vitro was used to evaluate the effect of GIP on sodium-glucose co-transporter (SGLT). Motility of small intestine was measured by intestinal transit after oral administration of a non-absorbed marker. Intraperitoneal administration of GIP inhibited glucose absorption in wild-type mice in a concentration-dependent manner, showing maximum decrease at the dosage of 50 nmol/kg body weight. In glucagon-like-peptide-1 (GLP-1) receptor-deficient mice, GIP inhibited glucose absorption as in wild-type mice. In vitro examination of [¹⁴C]-glucose uptake revealed that 100 nM GIP did not change SGLT-dependent glucose uptake in wild-type mice. After intraperitoneal administration of GIP (50 nmol/kg body weight), small intestinal transit was inhibited to 40% in both wild-type and GLP-1 receptor-deficient mice. Furthermore, a somatostatin receptor antagonist, cyclosomatostatin, reduced the inhibitory effect of GIP on both intestinal transit and glucose absorption in wild-type mice. These results demonstrate that exogenous GIP inhibits intestinal glucose absorption by reducing intestinal motility through a somatostatin-mediated pathway rather than through a GLP-1-mediated pathway.     

Research of anin vitro model to study the expression of fatty acid-binding proteins in the small intestine

In order to find anin vitro model for studying the regulation of the biosynthesis of the cytoplasmic Fatty Acid-Binding Proteins (FABPc) expressed in the small intestine, Intestinal- and Liver-(I- and L-) FABPc expressions were tested by Northern blotting in 8 normal or cancerous intestinal cell lines from man, mouse and rat and in organ culture of mouse jejunal explants. Neither I- nor L-FABPc mRNA was detected in any cell strains tested except in the highly differentiated human enterocyte-like intestinal cell line Caco-2. In this line, Northern blot analysis revealed a single messenger of about 0.7 kb corresponding to the L-FABPc. A two-fold increase in mRNA L-FABPc occurred in differentiated Caco-2 cells treated for 7 days with 0.05 mM bezafibrate, a peroxisome-proliferating hypolipidemic drug. The lack of I-FABPc messengers in this strain led us to seek anotherin vitro model. I- and L-FABPc messengers were found using an organ culture of mouse jejunal explants. A clear rise in I- and, especially, L-FABPc mRNA levels occurred 6 and 24 hr after the addition of 0.05 mM bezafibrate in the culture medium. Our results demonstrate, to our knowledge for the first time, that: 1) organ culture of intestinal explants provides a useful model for studyingin vitro the simultaneous regulation of I- and L-FABPc expressions, 2) biosynthesis of L-FABPc may be exploredin vitro using the Caco-2 cell line, 3) fibrate peroxisome-proliferators exert a direct effect on I- and L-FABPc expression in the small intestine, 4) L-FABPc expression seems to be more sensitive to fibrate action than is I-FABPc expression.Abbreviations I-FABPc cytosolic Intestinal Fatty Acid-Binding Protein - L-FABPc cytosolic Liver Fatty Acid-Binding Protein - bp base pair - EDTA Ethylenediamine Tetraacetic Acid - DMSO Dimethyl Sulfoxide - BSA Bovine Serum Albumin - DMEM Dulbecco's Modified Eagle's Medium - HBSS Hanks Balanced Salt Solution     

Lipopolysaccharide of Escherichia coli, polyamines, and acetic acid stimulate cell proliferation in intestinal epithelial cells

Summary Our aim was to examine whether lipopolysaccharide of Escherichia coli, polyamines of dietetic and/or bacterial origin, and products of the bacterial metabolism influence cell proliferation in epithelial cells from the colon and small intestine. Lipopolysaccharide of Escherichia coli 0111:B4 was incubated with cultures from human colonic mucosa. The mitoses were arrested with Vincristine and the total number of metaphases per crypt was counted. In addition, lipopolysaccharide was incubated with a human colonic epithelial cell line from adenocarcinoma (LS-123 cells) and with a nontransformed small intestinal cell line from germ-free rats (IEC-6 cells) for 24 h. In the last 4 h, the cells were labeled with tritiated thymidine. The cells were incubated with putrescine, cadaverine, and spermidine at 10⁻¹¹–10⁻³ M and with acetic acid (10⁻⁵–10⁻¹ M), acetaldehyde (10⁻¹⁰–10⁻⁴ M) and ammonium chloride (1–20 mM). Lipopolysaccharide of Escherichia coli increased the number of arrested metaphases in human colonic crypts and DNA synthesis in L-123 and IEC-6 cells (P<0.001). All polyamines increased DNA synthesis in the colonic and small intestinal cell lines, the effects being more marked for putrescine (P<0.001). The higher concentrations of acetic acid increased DNA synthesis in both epithelial cell lines (P<0.001). Acetaldehyde slightly decreased DNA synthesis in LS-123 cells at cytotoxic concentrations. Ammonium chloride did not significantly affect DNA synthesis. The final concentration of nonionized ammonia was less than 3%. It is concluded that lipopolysaccharides of Escherichia coli and intraluminal factors derived from microorganisms increase cell proliferation in human colonic crypts and intestinal epithelial cell lines.     

The Circadian Variations In the Eithelial Growth of the Hamster Cheek Pouch: Quantitative Analysis of Dna Distributions*

The pronounced diurnal rhythm in DNA distribution of the hamster check pouch epithelium both in the S fraction and in the (G₂+ M) fraction was compared with previous studies of the changes in tritiated thymidine labelling index and mitotic activity. the DNA distributions were obtained by flow cytometry after ultrasonic disaggregation of the isolated epithelium into a suspension of single nuclei. the DNA distributions were analysed with the computer program of J. Fried (1976) and by planimetry. the S fraction was higher than the autoradiographic labelling index during the whole 24 hr period. Only the computer fitted S fraction and the labelling index had the same difference between maximal and minimal values, and maxima at the same time of day. the DNA distributions showed a diurnal release of G₁ cells into S phase proceeding through (G₂+ M) phase and returning to G₁ phase within a 24 hr period.     

An autoradiographic study of the origin of intestinal blastemal cells in the newt, Notophthalmus viridescens.

Fifty adult newts were used in this investigation; in 44 animals, the intestine was transected perpendicular to its longitudinal axis approximately midway between pylorus and rectum. The free ends of the intestine were held in apposition with a single suture and replaced into the coelom. The animals were injected intraperitoneally with [³H]thymidine from 0 to 35 days after transection of the intestine and killed 6 hr later. In nontransected, control intestines, the only tissue that incorporated [³H]thymidine was the mucosal epithelium. In transected intestines, only the mucosal epithelium labeled in animals which had been injected with [³H]thymidine from 0 to 4 days after the intestine was incised. Later on, serosal cells and smooth muscle cells of the intestinal stump underwent morphological alteration, initiated the incorporation of [³H]thymidine into DNA, and began replication. At 6 days after transection, serosal cells adjacent to the plane of transection were incorporating [³H]thymidine and, at 12 days, smooth muscle cells at the transected surface were labeling. It seems probable that they both furnished cells to the intestinal blastema; the lining epithelium of the mucosa, however, did not appear to contribute to the blastema proper.     

Permeation of Four Oral Drugs Through Human Intestinal Mucosa

The pharmaceutical industry is in need of rapid and accurate methods to screen new drug leads for intestinal permeability potential in the early stages of drug discovery. Excised human jejunal mucosa was used to investigate the permeability of the small intestine to four oral drugs, using a flow-through diffusion system. The four drugs were selected as representative model compounds of drug classes 1 and 3 according to the biopharmaceutics classification system (BCS). The drugs selected were zidovudine, propranolol HCl, didanosine, and enalapril maleate. Permeability values from our in vitro diffusion model were compared with the BCS permeability classification and in vivo and in vitro gastrointestinal drug permeability. The flux rates of the four drugs were influenced by the length of the experiment. Both class 1 drugs showed a significantly higher mean flux rate between 2 and 6 h across the jejunal mucosa compared to the class 3 drugs. The results are therefore in line with the drugs’ BCS classification. The results of this study show that the permeability values of jejunal mucosa obtained with the flow-through diffusion system are good predictors of the selected BCS class 1 and 3 drugs’ permeation, and it concurred with other in vitro and in vivo studies.