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Background & Aims: The DNA mismatch repair gene human MSH2 shows a germline mutation in certain family members with hereditary nonpolyposis colorectal cancer. There is an increased risk of colorectal cancer in patients with ulcerative colitis (UC) with extensive disease of > 8 years' duration; however, specific constitutional predisposing genetic abnormalities have not yet been identified., Methods: A germline human MSH2 abnormality was sought in patients with UC with high-grade dysplasia or carcinoma., Results: After direct sequencing of exon 13 and flanking regions of human MSH2, a germline T to C substitution was shown at the -6 intronic splice acceptor site of exon 13. This substitution was found in 14 of 53 patients with UC with high-grade dysplasia or carcinoma (26%) compared with 4 of 36 high-risk patients with UC without dysplasia or cancer (11%) (P < or = 0.04) and in 7 of 80 healthy adult blood donors (9%) (P < or = 0.003). The patients with UC who had the substitution were three times more likely to develop neoplasia than patients with UC who did not carry it., Conclusions: An intronic splice-site substitution in the human MSH2 gene is present in the general population but may predispose to cancer in the setting of UC.

Background/aims: In long-term extensive ulcerative colitis, aneuploidy occurs earlier and loss of heterozygosity for p53 (p53 LOH) later during histological progression towards carcinoma. This study determined the time of onset of p53 mutation in this progression., Methods: We developed a rapid, sensitive screening assay for p53 mutations at codon 248. The geographic distribution of this p53 mutation was mapped in two fresh colectomy specimens with mutations of codon 248 (1 cancer, 1 dysplasia) and correlated with patterns of clonal expansion, histological progression, and allelic loss. Numerous samples from throughout both colons were analyzed (216 for histology, 142 for DNA content, 104 for mutation, and 41 for p53 LOH)., Results: p53 mutation correlated highly with histological grade and was distributed more extensively than p53 LOH. Mutation, but not LOH, was also found in diploid, nondysplastic colonic mucosa adjacent to dysplastic areas., Conclusions: These findings suggest that p53 mutation appears to be an early genetic event that precedes p53 LOH. The very close correlation of p53 mutation with aneuploidy (P > 0.0001) emphasizes the role of normal p53 at the G1 checkpoint to help prevent entry of genetically damaged cells into the cell cycle.

The objective of the present study was to determine whether abnormal epithelial DNA content (aneuploidy) in colonic biopsy specimens from ulcerative colitis (UC) patients correlated with and predicted histological progression to dysplasia. Aneuploidy was absent in 20 low-cancer risk patients. In 81 high-cancer risk patients aneuploidy correlated significantly with the severity of histological abnormality (negative, indefinite, dysplasia, or cancer). Statistically our data suggest that many more biopsy specimens than are usually taken are needed to detect focal dysplastic lesions. Prospective study of 25 high risk patients without dysplasia revealed 5 with aneuploidy, all of whom progressed to dysplasia in 1-2.5 years, whereas 19 patients without aneuploidy did not progress to either aneuploidy or dysplasia within 2-9 years. Our data indicate that aneuploidy in mucosal biopsy specimens correlates with histological grade and identifies a subset of patients without dysplasia who are more likely to develop it. It was concluded that more frequent and extensive colonoscopic surveillance of this minority subset of high risk patients and less frequent surveillance in the remaining majority may reduce cost and detect more curable lesions.

Neoplastic progression in patients with chronic ulcerative colitis (UC) is characterized by the development of epithelial dysplasia, which is accompanied by genetic abnormalities that can be detected by flow cytometric and molecular biologic methods. Distribution of and correlation between histologic abnormalities, DNA content, and loss of heterozygosity for a p53 allele (p53 LOH) in the colons of nine UC patients were analyzed. Loss of a p53 allele was found in 85% (22/26) of biopsy specimens classified histologically as carcinoma, 63% (25/40) of biopsy specimens with high grade dysplasia, and 33% (7/21) of biopsy specimens with low grade dysplasia. Loss of heterozygosity for p53 was also found in 9% (5/57) of biopsy specimens indefinite for dysplasia and in 1/18 biopsy specimens negative for dysplasia, showing that this genetic change may occur early in the histological progression towards carcinoma. Aneuploid DNA contents were more common than p53 LOH in regions with negative, indefinite or low grade dysplastic histology; moreover, p53 LOH was detected only in aneuploid cells and not in diploid epithelium. Aneuploidy alone was not as specific a marker for the concomitant presence of dysplasia or carcinoma in a biopsy sample as aneuploidy combined with p53 LOH. These findings show that aneuploidy may precede both p53 LOH and epithelial dysplasia. Two UC patients' colons contained geographically separated clones of cells with different aneuploidies that also showed loss of different p53 alleles, suggesting that neoplasia may arise within different populations of cells in separate areas of the same colon.

Flow cytometry was used to detect the presence and assess the distribution of aneuploid cell populations in eight proctocolectomy specimens from patients with ulcerative colitis. Mucosal samples were taken according to a systematic protocol for flow cytometry, the surrounding tissue was examined histologically, and the distributions of flow cytometric and histologic abnormalities were "mapped" within each resected colon. Two resection specimens that were negative for dysplasia lacked aneuploid cell populations. Four resection specimens with final case diagnoses of dysplasia or Dukes' stage A carcinoma had 1-5 regions of aneuploidy or increased 4N (G2/tetraploid) cell populations located in discrete areas of the colon. Two specimens with dysplasia or Dukes' stage C carcinoma each had 14-15 different, often overlapping, regions of aneuploidy or increased 4N (G2/tetraploid) cell populations involving large portions of the colonic mucosa. Analysis of the DNA content of the invasive portion of the tumor from the specimen with a Dukes' stage C carcinoma showed a single aneuploid cell population. The results show that single or multiple aneuploid cell populations are often present in colons resected for ulcerative colitis with dysplasia or early cancer. The distribution of these aneuploid cell populations suggests that each represents a clone of cells that has expanded to occupy a discrete region of colonic mucosa. Additional genetic errors may result in multiple aneuploid cell populations that may be associated with an increased risk of developing cancer. These data, therefore, are consistent with the hypothesis that genomic instability and clonal evolution are associated with the progression to dysplasia and carcinoma in ulcerative colitis. Because flow cytometry can measure aneuploid cell populations in colonoscopic mucosal biopsies, it may prove to be complementary to histology for detecting patients with ulcerative colitis who are at risk for neoplastic progression.

Mutations in the first exon of the c-Ki-ras protooncogene were analyzed in carcinomas and dysplasias from patients with sporadic colon cancer and chronic ulcerative colitis by a combination of histological enrichment, cell sorting, polymerase catalyzed chain reaction, and direct sequencing. In contrast to sporadic colon carcinomas, where 52% (11 of 21) contained mutations in codon 12, only 1 of 28 samples of ulcerative colitis associated carcinoma or dysplasia contained a c-Ki-ras mutation, despite the presence of aneuploid cell populations. These results suggest that a different genetic pathway for tumor progression may exist between sporadic colon carcinoma and carcinomas arising in chronic ulcerative colitis.

A neodymium YAG (Nd:YAG) laser was evaluated in a dog ulcer model used in the same manner as is recommended for bleeding patients (power 55 W, divergence angle 4 degrees, with CO2 gas-jet assistance). The experiments were performed during sterile laparotomy in heparinized dogs. Bleeding gastric ulcers were photocoagulated until bleeding stopped and then examined histologically 7 days later when depth of tissue injury was maximal. In the first series of experiments, the Nd:YAG laser was compared with the 7-W argon laser in the same dogs. Both lasers stopped bleeding from all experimental ulcers. The 55-W Nd:YAG laser caused full-thickness injury to the gastric wall beneath 11 of the 14 treated ulcers, whereas the 7-W argon laser caused no full-thickness injury beneath 14 treated ulcers. In a second series of experiments, we tried to determine whether varying exposure times with the 55-W Nd:YAG laser would make it less injurious; it did not. In a third series of experiments, the 55-W Nd:YAG laser was tested with and without CO2 gas-jet assistance in order to determine if this would affect the depth of injury; it did not. In the final series of experiments, the wattage of the Nd:YAG laser was varied to see if this would reduce depth of injury; lower wattage did not stop bleeding, and intermediate and higher wattages did stop bleeding but did not reduce depth of injury. We conclude that the 55-W Nd:YAG laser as it is currently used clinically produces deeper tissue damage than the argon laser in our animal model. This damage is not reduced by changes in power, duration of exposure, or the presence of gas-jet assistance.

To determine whether laxatives alter the proctoscopic and morphological appearances of the human rectum, 10 normal subjects were studied prospectively, and the following manipulations were assessed in a randomized, blinded manner: no treatment; oral mannitol to induce diarrhea; isotonic saline enema; Fleet's Phospho-Soda enema; and bisacodyl (Dulcolax), 10 mg, by enema or suppository. The rectal mucosa after mannitol-induced diarrhea, or after saline enema could not be distinguished from untreated rectum by proctoscopy, light microscopy, or scanning electron microscopy. Fleet's enema, and bisacodyl invariably changed proctoscopic appearances, and frequently altered light and scanning microscopic aspects. Both Fleet's enema and bisacodyl caused sloughing of surface epithelium. In addition, bisacodyl decreased the uptake of hematoxylin and eosin by crypt epithelial cells so that the affected cells had a partially erased appearance (16 of 25 biopsies examined by light microscopy). The lamina propria of 3 of these 25 biopsies contained polymorphonuclear cells. Transmission electron microscopy revealed that the abnormal crypt epithelial cells contained fewer cytoplasmic organelles and less nuclear chromatin. All lesions resolved within 7 days. Fleet's enema and bisacodyl by rectum may mislead the proctologist and the pathologist by altering normal rectal mucosa.

Desferrioxamine (DFO) is an iron chelating agent that, when administered orally, interferes with gut absorption of inorganic iron and, when administered parenterally, binds body iron and is excreted as ferrioxamine in bile and urine. Studies were carried out in normal and iron-deficient male rats and in normal, iron-replete male volunteers to investigate the blocking action of parenteral DFO on the absorption of radioiron. Radiolabeled ferrous ammonium sulfate, transferrin iron, or hemoglobin iron was injected directly into the jejunum of rats with or without intramuscular injections of DFO. Radioiron administered as ferrous sulfate or as transferrin iron was given to the volunteers by mouth or by direct duodenal infusion, respectively, with or without intravenous infusions of DFO. In iron-deficient rats, intramuscular DFO injections commencing 1 h before direct jejunal injection of radioiron significantly blocked absorption of inorganic iron (26% with DFO, 64% without DFO), transferrin iron (4% with DFO, 69% without DFO), and hemoglobin iron (3% with DFO, 19% without DFO). In normal rats, DFO injections also significantly blocked absorption of inorganic iron and transferrin iron. In normal volunteers, intravenous DFO infusions commencing 1 h before administration of radioiron significantly blocked absorption of physiologic doses of inorganic iron (3% with DFO, 21% without DFO) and transferrin iron (1% with DFO, 20% without DFO). The quantity of radioiron excreted in urine by both rats and humans with administration of DFO did not account for the observed decrement in absorption of radioiron. Biochemical analysis of rat intestinal mucosal scrapings after injection of DFO and administration of radioiron demonstrated the accumulation of a small molecular weight fraction containing iron that was ferrioxamine (iron-chelate) complex. We conclude that parenterally administered DFO can enter the small intestinal mucosa, bind intracellular iron, and block iron absorption. Parenteral DFO blocks the absorption of inorganic iron, transferrin iron, and hemoglobin iron, suggesting that all three iron species enter a common chelatable pool within the small intestinal mucosa and may share a common pathway of absorption.

Morphologic and physiologic experiments in rodents have demonstrated differences between jejunal and ileal fat absorption. Compared with the rat jejunum, absorbed lipid particles within rat ileal absorptive cells are larger and exit at a slower rate. To evaluate the relevance of these observations to humans, we studied jejunal and ileal ultrastructure in 3 volunteers, each of whom had an intact small intestine and an ileostomy postcolectomy for ulcerative colitis. Proximal jejunal biopsy specimens were obtained via a hydraulic tube after an overnight fast and again after a 20-min intrajejunal lipid infusion. On a separate day, terminal ileal biopsy specimens were taken via the stoma with a small steerable suction biopsy tube after an overnight fast and again after a 20-min intraileal infusion of the same lipid mixture. One volunteer underwent biopsy after a 60-min ileal infusion of a digested meal of higher lipid content. Electron microscopy of fasting human jejunal absorptive cells revealed obvious smooth endoplasmic reticulum in the extreme apical region beneath the terminal web; very low density lipoprotein particles were observed within smooth endoplasmic reticulum and Golgi cisternae. In contrast, fasting human ileal absorptive cells contained less apical smooth endoplasmic reticulum and fewer or no very low density lipoprotein particles. After the 20-min infusion of lower-lipid content, human jejunal and ileal absorptive cells were indistinguishable because they contained fat particles of the same size and number within smooth endoplasmic reticulum, Golgi cisternae, and extracellular spaces. After the 60-min ileal infusion of higher-lipid content, human ileal absorptive cells appeared to be the same as those of the human jejunum after similar lipid infusions. Our observations of the ultrastructural similarity in human jejunal and ileal absorptive cells after lipid infusions contrasts with those in rodents and may reflect species-specific differences in mechanisms of fat absorption.

There is uncertainty regarding the value of endoscopic biopsy surveillance in Barrett's esophagus because, in retrospective studies, some patients with high-grade dysplasia in endoscopic biopsy specimens have had unexpected advanced adenocarcinoma discovered at the time of esophageal resection. We compared the accuracy of preoperative endoscopic biopsy diagnoses with the final pathologic diagnoses in esophagectomy specimens in 4 patients who had both high-grade dysplasia and intramucosal carcinoma and 4 other patients who had only high-grade dysplasia preoperatively. The histologic lesions in all 8 patients were documented in intact mucosa with no gross evidence of neoplasia by endoscopy. The preoperative diagnoses were defined with an endoscopic biopsy protocol in which specimens were taken with large-channel biopsy forceps at least every 2 cm throughout the length of Barrett's epithelium. Final pathologic diagnoses derived from detailed analysis of the resected specimens confirmed high-grade dysplasia without carcinoma in 4 patients and intramucosal carcinoma in 2 patients. The remaining 2 patients with a preoperative diagnosis of intramucosal carcinoma had focal submucosal invasion by carcinoma in the resected specimens, but no involvement of the muscularis propria or adventitial lymph nodes. Because the natural history of high-grade dysplasia is not known, the decision to operate on patients with this lesion must be carefully weighed and individualized for each patient. Two of our patients who underwent esophageal resection for high-grade dysplasia without cancer died, one immediately postoperatively and the other 9 mo later after a postoperative stroke. Once intramucosal carcinoma is documented, surgery should be considered if the patient is an acceptable operative risk. We conclude that systematic preoperative endoscopic biopsy of intact mucosa in Barrett's esophagus can correctly detect high-grade dysplasia, either alone or in combination with early, treatable adenocarcinoma.

With minimal transmission loss a high power argon laser (10 w) was coupled to a waveguide consisting of a flexible, single, coated, quartz fiber encased in a protective polyethylene tube. This waveguide can be passed down the biopsy channel of any standard fiberoptic endoscope. An aiming light improves accuracy. Safety devices were developed to protect the subject and the operator. Each of 8 heparinized mongrel dogs had three superficial erosions created endoscopically in the fundal gland mucosa by a jet of warm 0.1 N HC1. In each animal two lesions were photocoagulated with the laser and the third was left as a control. The animals were killed at 0, 4, 7, 10, and 14 days, and the erosions were examined histologically. By 14 days all lesions were covered by normal surface epithelium. Parietal and chief cells had returned to untreated erosions at 14 days but not to all lasered lesions. Only rarely did the lasered lesions penetrate through the muscularis mucosae into the submucosa. High power argon laser photocoagulation is now feasible through standard endoscopes. These data are sufficiently promising to encourage further evaluation of laser photocoagulation in a variety of animal models.

Barrett's esophagus develops as a complication of chronic gastroesophageal reflux and predisposes patients to the development of dysplasia and adenocarcinoma of the esophagus. Because light microscopy of dysplasia in Barrett's esophagus shows diminished or absent mucus, we used transmission electron microscopy to compare cytoplasmic organelles required for mucus production in dysplastic and nondysplastic esophageal columnar epithelium. These observations of the rough endoplasmic reticulum, Golgi apparatus, and secretory granules were correlated with histologic interpretations and flow cytometric measurements of abnormalities of DNA content. Ultrastructural abnormalities included depletion and alteration of organelles required for mucus biosynthesis. These abnormalities often were accompanied by cells with markedly distended rough endoplasmic reticulum and massive accumulation of cytoplasmic glycogen aggregates. All 9 patients who had Barrett's dysplasia with or without early adenocarcinoma had ultrastructural abnormalities, as did 3 of 8 patients whose biopsy histology was indefinite for dysplasia. Abnormalities measured by flow cytometry correlated well with the presence of these ultrastructural aberrations. All 9 patients with Barrett's dysplasia with or without early adenocarcinoma had abnormalities observed by electron microscopy and aneuploidy or increased G2/tetraploid fractions measured by flow cytometry. Two of the 3 patients whose biopsies were indefinite for dysplasia and who had ultrastructural abnormalities also had aneuploidy or increased G2/tetraploid fractions. Neither ultrastructural nor flow cytometric abnormalities were found in the remaining 5 patients whose biopsies were indefinite for dysplasia, in 19 of 22 patients with Barrett's specialized metaplasia, or in any of the 7 patients with gastroesophageal reflux disease without Barrett's specialized metaplasia. Two of the 22 patients with Barrett's specialized metaplasia had distended rough endoplasmic reticulum in rare cells, and one other had an aneuploid cell population. We conclude that neoplastic progression in Barrett's esophagus is associated with abnormalities of cytoplasmic organelles required for mucus production. With few exceptions, these ultrastructural aberrations correspond to the presence of dysplasia or of aneuploidy or increased G2/tetraploid fractions. Electron microscopy and flow cytometery detect abnormalities associated with the development of dysplasia and cancer in Barrett's esophagus that may be biologically significant.

The coagulative efficacy of a "high power" argon laser which delivers 6.5 +/- 1.0 w was compared to that of a "low power" argon laser which delivers 1.0 +/- 0.1 w. The wave-guide angle of divergence was 8 degrees. For the high power laser, the distance between the wave-guide tip and the mucosa varied from 1.0 to 1.5 cm with a delivered power density range of 160 to 487 w per cm2. For the low power laser, the distance between the tip and mucosa varied from 0.7 to 1.3 cm with a power density of 35 to 146 w per cm2. Group A consisted of acute experiments in 6 heparinized dogs in which 51 standard-sized acute gastric ulcers extending into the submucosa were made at laparotomy via a large gastrotomy. Ulcer bleeding rates were quantified into three categories of severity. Within each category, ulcers were randomized to high power, low power, or untreated control. All 19 low power-treated ulcers and 16 untreated controls continued bleeding; 13 of 16 high power-treated ulcers stopped bleeding completely. Representative ulcers were examined histologically. Group B consisted of chronic experiments on 31 ulcers in 7 unheparinized dogs. These ulcers were either treated with high power or left as untreated controls. Dogs were killed and the ulcers were examined histologically at 7, 14, and 28 days. Only rarely did the laser injury penetrate into the muscularis externa. There were no perforations. By 14 days, all lesions were covered with normal surface epithelium. These data encourage further development of congruent to 7.0 w argon laser photocoagulation for eventual clinical use in man.

A previously healthy 67-yr-old man presented with progressive dementia over an 11-mo period. Evaluation revealed evidence of malabsorption. Jejunal biopsy established the diagnosis of Whipple's disease. No other etiology for the patient's dementia was uncovered. Treatment with trimethoprim-sulfamethoxazole resulted in rapid elimination of Whipple's bacilli from the jejunum and complete reversal of the patient's dementia over a 6-mo period. Significant levels of trimethoprim and sulfamethoxazole were easily quantitated in the cerebrospinal fluid during therapy. There is increasing recognition of progressive neurologic disease in patients with Whipple's disease who were treated with tetracycline. The reversal of presumed central nervous system disease in this case suggests that drugs that penetrate the blood-brain barrier might be preferable for the initial treatment of Whipple's disease.

By correlating morphological observations with quantitative measurements of net water transport, we determined whether bile salts altered colonic absorptive cells. Epithelial alteration was equivocal and water absorption was uninhibited during infusions of 1 mM deoxycholate or of concentrations of taurocholate less than 10 mM. In contrast, 3 mM deoxycholate and greater than 10 mM taurocholate caused severe altertion of colonic epithelium and inhibited water absorption. These studies suggest that bile salts in the low concentrations normally found within the colon have little effect on colonic structure or water absorption. On the other hand, abnormally high concentrations of bile salts do alter colonic mucosal structure and function.

An instrument has been developed which creates an experimental model of an acute bleeding gastric ulcer. The diameter and depth of these gastric ulcers are reproducible. The instrument can be used endoscopically or at laparotomy. Using this ulcer model nonsurgical modalities for the treatment of upper gastrointestinal bleeding can be compared in a controlled manner. This standard experimental model may also facilitate comparison of results among different research groups.

We performed a retrospective evaluation of 243 rectal biopsies from 90 patients who eventually had Crohn's disease proven clinically or by surgery. A portion of each rectal biopsy was serially sectioned. Twenty-five of the 90 patients (28%) had epithelioid granulomas. Half of these patients had an epithelioid granuloma in only one of two or more biopsies. Sixteen percent of these granulomas were so small as to be seen in only six or less successive serial 4-microM sections. This high yield of granulomas is probably attributable to the examination of at least 90 serial sections, usually from each of two rectal biopsies per patient. Using partial serial sectioning, epithelioid granulomas were found almost as frequently in grossly normal as in grossly abnormal appearing mucosa. No granulomas were seen in suitable controls including normals and patients with ulcerative colitis or other diseases. When the differential diagnosis between idiopathic ulcerative colitis and Crohn's disease is uncertain, we recommend taking two rectal biopsies and serially sectioning part of each.

The value of endoscopic surveillance biopsy for dysplasia and carcinoma in patients with Barrett's esophagus is controversial. One reason is that the available histologic criteria are not adequate to separate patients with lesser degrees of dysplasia or predysplastic changes who are at increased risk for carcinoma and therefore require more frequent surveillance from those patients who are not at increased risk. We used flow cytometry and histology to evaluate 317 biopsy specimens from 64 consecutive patients who were in a cancer surveillance program for Barrett's esophagus and 3 additional patients with adenocarcinoma in Barrett's esophagus. Specimens from 10 patients had aneuploid cells; 9 of these had dysplasia or carcinoma, or both, but 1 patient had only specialized metaplastic epithelium. Twenty specimens ahd G2/tetraploid fractions greater than 6%; all 20 came from patients who had cancer or dysplasia, or were indefinite for dysplasia. All patients with dysplasia or adenocarcinoma had evidence of genomic instability (aneuploidy) or abnormalities of mucosal proliferation by flow cytometry, even when the dysplasia was focal or difficult to recognize histologically. In a small subset of patients with specialized metaplastic epithelium whose specimens were histologically negative or indefinite for dysplasia, the mucosa had aneuploid cell populations or proliferative abnormalities that were otherwise found only in dysplasia or carcinoma. Additional study may prove that this subset of patients merits more frequent endoscopic biopsy surveillance because of an increased risk for developing carcinoma. Because the abnormalities we have detected by flow cytometry correlate well with the conventional histologic diagnoses of dysplasia and carcinoma, they may prove to be a valuable objective adjunct in the diagnosis of dysplasia and carcinoma in Barrett's esophagus.

A 39-year-old man with severe bullous pemphigoid developed overwhelming diarrhea after 5 weeks' treatment with 150 mg of cyclophosphamide and 60 mg of prednisolone daily. Jejunal and ileal biopsies showed severe mucosal injury and tiny 2- to 4-mu organisms on the epithelial surfaces. Similar organisms were seen in smears of jejunal fluid. Electron microscopic examination of jejunal biopsies showed these spherical bodies to be trophozoites, schizonts, microgametocytes, and macrogametocytes typical of the genus Cryptosporidium. Diarrhea resolved 2 weeks after discontinuation of cyclophosphamide and coincided with disappearance of Cryptosporidia from the jejunal biopsies. Immunosuppression may have predisposed this patient to cryptosporidial diarrhea. Cryptosporidiosis is another infection which can be diagnosed by small bowel biopsy. When immunosuppressed patients develop severe diarrhea, opportunistic infection with this and other organisms should be considered as the possible cause.

The effect of bisacodyl on intestinal structure and function was investigated. Net water transport was measured under steady state conditions in vivo during single pass infusions of rodent and of human intestinal segments. Each segment served as its own control. Bisacodyl inhibited water absorption in rat jejunum, ileum, and colon. The degree of inhibition was linearly related to the logarithm of the bisacodyl concentration over the range of 0.05 to 2.0 mg per 100 ml. In human jejunal segments, bisacodyl, 1 mg per 100 ml, caused net water secretion. Bisacodyl, 5 mg every 6 hr, increased ileostomy output by 15% when it was fed to 5 patients with established ileostomies. By light microscopy, bisacodyl, 2 mg per 100 ml, erased cytoplasmic and nuclear detail within surface absorptive cells of rat intestine. By electron microscopy, the involved cells contained sparse and abnormal cytoplasmic organelles and nuclei which were deficient in chromatin. These results suggest that the laxative effect of bisacodyl is related to its ability to inhibit intestinal water absorption. Reduced absorption may be secondary to changes in surface absorptive cells.