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Background: Ingested peanut agglutinin stimulates colonic proliferation in humans. In rats, ingested peanut agglutinin stimulates hormone release and proliferation in the small and large intestines. Peanut agglutinin is absorbed into the circulation but little is known about the systemic effect of this lectin. Therefore, we studied the effect of intravenous peanut agglutinin on hormone release and intestinal growth., Method: Six rats per group received peanut agglutinin infusion at 0, 2, 20 or 200 microg/rat/day for 6 days via the right jugular vein. Organ weights were measured, pancreatic enzymes, DNA, RNA and protein levels were analysed. Plasma hormones were measured by radioimmunoassay. All tissues were examined histologically. Small intestinal and colonic proliferation rates were estimated by metaphase arrest., Results: High-dose peanut agglutinin significantly reduced the wet weight of the stomach by 7% (P < 0.05) and large intestine by 10% (P < 0.05). Peanut agglutinin dose-dependently released enteroglucagon; low-, medium- and high-dose by 64%, 126% (P < 0.01) and 180% (P < 0.01), respectively, and glucagon-like peptide-1 by 127% (P < 0.01), 169% (P < 0.01) and 315% (P < 0.001), respectively. Peanut agglutinin had no effect on cholesystokinin, gastrin or insulin levels. Peanut agglutinin, low-, medium- and high-dose stimulated proliferation in the mid colon by 42% (P < 0.01), 30% and 38%, respectively. Only high-dose peanut agglutinin stimulated proliferation in the distal colon by 54% (P < 0.01). No histological changes were evident in any tissue., Conclusion: Intravenous peanut agglutinin released hormones and stimulated colonic proliferation. Proliferation of the small intestine seen after ingestion of peanut agglutinin in previous studies appears to require luminal contact between enterocytes and the lectin. Possible clinical applications include reversal of atrophy during total parenteral nutrition, anastomotic healing after surgery and restoration of mucosa integrity in colitis.

In an attempt to demonstrate the relationship between aberrant crypt foci (ACF) and subsequent colonic neoplasms, we investigated the distribution of ACF in the dimethylhydrazine (DMH) model of colonic carcinogenesis in the rat. DMH was given to male Wistar rats by s.c. injection in a dosage of 15 mg/kg body weight once a week for 19 weeks. As a result, eight poorly differentiated, mucin-secreting carcinomas, two well-differentiated tubular adenocarcinomas, and four adenomas developed in 35 rats autopsied at 24 weeks after the first injection of DMH. The location of each type of tumor was site specific. Poorly differentiated, mucin-secreting carcinomas of signet-ring type occurred only in the proximal colon; the mean location of these lesions was 17.6 +/- 3.8% (SE; range, 0-39%) of the length of the colon. Well-differentiated tubular adenocarcinomas and adenomas developed in the distal colon; the mean location of these lesions was 76.7% +/- 4.9 (SE; range, 60-90%) of the length of the colon. There was a mean number of 276 +/- 29 (SE) ACF per colon; these were present at between 40 and 90% of the colonic length, peaking at 70%. We conclude that ACF are marker lesions for colonic neoplasms, but only in the distal colon where tumors follow the adenoma-carcinoma sequence; this is not so for the proximal colon, where poorly differentiated, mucin-secreting carcinomas are found. These findings suggest that these latter tumors well may arise de novo and indicate that studies that attempt to correlate ACF with subsequent tumor formation must take cognizance, not only of the site, but also of the tumor type.

Crypt fission is now established as an important mechanism of intestinal growth and regeneration. It has been proposed that increased crypt size is the stimulus for crypt fission, because crypts preparing for fission are generally larger. Consequently, we investigated the effects of epidermal growth factor (EGF) and dimethylhydrazine, which are both known to stimulate crypt cell proliferation, on crypt fission in the rat intestine. We also examined whether the effects of EGF on both proliferation and crypt fission are modified by the pretreatment with dimethylhydrazine for 16 weeks, dimethylhydrazine was then discontinued for 8 weeks, followed by intravenous infusion of EGF for 1 week. There were four groups: vehicle alone, EGF alone, dimethylhydrazine alone, and dimethylhydrazine followed by EGF infusion. The rats were killed at 25 weeks and rates of intestinal crypt cell production, crypt size, and crypt fission were determined. Intravenously infused EGF significantly increased crypt cell production rate, but the magnitude of the effect decreased from the proximal to the distal colon. EGF caused an increase in crypt area, possibly reflecting an increase in crypt size. Importantly dimethylhydrazine had no significant effect on crypt cell production rate nor on crypt area in the distal colon, but it did cause an increase in crypt area in the mid-colon. The crypt fission index was significantly decreased by EGF and increased by dimethylhydrazine. There was no qualitative interaction between EGF and dimethylhydrazine. These results demonstrate the marked proliferative effect of intravenously infused EGF in the colon of orally fed rats, with significant site effects (P = 0.0007); the effect was greatest in the proximal colon and disappeared in the distal colon. The observation that EGF reduced crypt fission indicates that increased cell proliferation, per se, is not a stimulus for crypt fission. This is further supported by the observation that dimethylhydrazine increases crypt fission in crypts of normal size in the distal colon without significantly increasing cell proliferation. These results suggest that increasing crypt cellularity by proliferation is not sufficient to induce crypt fission, and factors other than increased crypt size by proliferation can control crypt fission. It is also probable that cell proliferation and crypt fission are independently regulated. Crypt fission appears to play a considerable role in the intestinal response to carcinogens.

In the small intestine and colon, administration of mutagens leads to the emergence of crypts populated by cells with a different, mutated phenotype. This is preceded by a transient rise in the frequency of crypts with a partially mutated phenotype, and the disappearance of these partially mutated crypts occurs contemporaneously with the attainment of a plateau value of the wholly mutated crypts. Here, using the mutagen ethyl nitrosourea and loss of glucose-6-phosphate dehydrogenase staining as a marker, we show that the plateau is reached at between 4.6 and 7 weeks in the colon and at 12 weeks in the small intestine of the same mice. Explanations for this difference have included differences in the stem cell cycle time of a single "master" stem cell or multiple stem cells occupying a stem cell "niche" with random loss after stem cell division. However, we demonstrate that the crypt fission index, or the incidence of crypts in fission, is some four times higher in the colon than in the small intestine at the time of ethyl nitrosourea injection, and propose an alternative hypothesis based on crypt fission as the mechanism for the more rapid evolution of wholly mutated crypts in the colon. The hypothesis should enable us to predict the results of future experiments, namely that the emergence of wholly mutated crypts is proportional to the crypt fission index.

While the proliferative effects of gastrin in the gastric fundus are well established, there is a considerable degree of confusion regarding the role of gastrin on the growth of the small intestine and colon. The hypothesis that gastrin is trophic throughout the gut was tested by giving three doses of pentagastrin and one of gastrin 17 to rats maintained by total parenteral nutrition (TPN). The rats were fed intravenously for one week, with the various peptides added to the TPN diet. The number of vincristine arrested metaphases per gland or crypt was then scored to determine the proliferative state. Both gastrin 17 and pentagastrin were found to be trophic in the gastric fundus, but not to the gastric antrum. A proliferative response was also seen in the duodenum, but with little evidence of a dose response element. No effect on small bowel weight was seen, and no proliferative effect was noted in the mid small bowel, thus the duodenal effect could be attributed to a local action of increased acid output on the duodenum, not a general role throughout the small intestine. No proliferative effects of pentagastrin or gastrin were seen in the colon. It is therefore concluded that the trophic role of gastrin is restricted to the gastric fundus and the proximal duodenum.

There is marked intestinal hypoplasia in the intestine of intravenously fed (TPN) rats. Recombinant urogastrone-epidermal growth factor (URO-EGF) reversed these changes by significantly increasing the length of the intestinal crypts. Crypt diameter, however, was not affected to the same extent. Few differences in labelling indices were seen between the orally fed and TPN groups, however, this was the consequence of the concomitant changes in crypt population. The number of mitoses and labelled cells per crypt, and thus the crypt cell production rates, were significantly decreased in the TPN group when compared to the orally fed. URO-EGF significantly increased both proliferative indices and the number of dividing cells per crypt. Crypt cell production in the small intestine was restored to those levels seen in the orally fed rats, moreover, labelling per crypt in the colon was increased to more than twice that of orally fed rats. The location of the mean labelling position and the half maximum labelling position followed the changes in crypt length in the small intestine, but to a lesser extent; thus the growth fraction was significantly increased in the TPN rats in comparison with the orally fed and the URO-EGF treated groups. Similar changes in these positions were seen in the colon, but the growth fraction was much reduced in the URO-EGF treated rats, as a consequence of the large increase in crypt length without a concomitant alteration in label distribution.

Colonic epithelial proliferation was investigated in three groups of rats, aged 3, 60 and 121 weeks. As reported in previous work, the crypts were markedly longer in the young rats, and the number of labelled cells per crypt was significantly greater. There was an upward movement of the marker positions derived from the distribution of labelled cells within the crypt of the young rats. This was a consequence of the increased crypt length, so that the growth fraction, as expressed as a percentage of crypt length, was the same. The proliferative changes between the young rats and the other aged rats were therefore effected by altering the size of the crypts, while maintaining the kinetic organisation. There was no evidence of any proliferative changes or changes in the growth fraction when the colons of the old rats were compared with those of the 60 week old rats.

Colonic epithelial cell division, cell migration, and cell transit were investigated in dogs given 300 micrograms.kg-1.day-1 of the prostaglandin E1 analogue, misoprostol, for 11 weeks. The animals were then injected with [3H]thymidine and killed at timed intervals. The distribution of labeled and mitotic cells within the crypts was determined by scoring autoradiographs. There were no significant differences in mitotic index or labeling index between the two groups. The data were pooled and converted to give crypt cell production rates of 51.1 +/- 11.1 (control) and 58.24 +/- 8.6 cells per crypt per hour (test). However, the crypt length and cell population were slightly, but significantly, greater in the misoprostol-treated group (P less than 0.01). The movement of the wave of labeled cells with time after injection was used to calculate the median cell migration rates, which were 23.50 +/- 3.03 cell positions per day (control) and 18.30 +/- 2.56 (test). Thus, misoprostol had no significant effect on either the cell migration rate or the transit rates.

Four groups of intravenously maintained rats were infused with 0, 5, 20 or 80 micrograms/rat/day of peptide tyrosine tyrosine (PYY) for 3 days. After 3 days the rats were injected with 1 mg/kg of vincristine in order to arrest cells entering metaphase and were killed 2 h later. The gastrointestinal tract was removed, weighed and fixed. Samples of small intestine and colon were stained, microdissected and the mean number of metaphases per crypt determined. No significant effect on intestinal tissue mass or the 2-hour collection of metaphases was observed. It is concluded that PYY is not trophic to the gastrointestinal tract.

Refeeding starved rats with a fibre free 'elemental' diet increased crypt cell production rate (CCPR) in the proximal small intestine but not in the distal regions of the gut. Little effect on CCPR was seen when inert bulk (kaolin) was added to the 'elemental' diet. Addition of a poorly fermentable dietary 'fibre' (purified wood cellulose) had little effect on intestinal epithelial cell proliferation except in the distal colon where it significantly increased CCPR. A more readily fermentable 'fibre' (purified wheat bran) caused a large proliferative response in the proximal, mid and distal colon and in the distal small intestine. A gel forming 'fibre' also stimulated proliferation in the distal colon. There was no significant correlation between CCPR and plasma gastrin concentrations, but plasma enteroglucagon concentrations were significantly correlated with CCPR in almost all the sites studied. Plasma PYY concentrations also showed some correlation with CCPR, especially in the colon. Thus, whilst inert bulk cannot stimulate colonic epithelial cell proliferation, fermentable 'fibre' is capable of stimulating proliferation in the colon, and especially in the distal colon: it can also stimulate proliferation in the distal small intestine and it is likely that plasma enteroglucagon may have a role to play in this process.

The aim of the present experiment was to investigate the role of hind gut fermentation in the proliferative response of the intestinal epithelium to dietary fibre. We have previously shown that refeeding starved rats with an elemental diet supplemented with fermentable dietary fibre (but not inert bulk) is capable of stimulating intestinal epithelial cell proliferation throughout the gastrointestinal tract. Three groups of 10 germ free (GF) rats and three groups of 10 conventional (CV) rats, were used. All groups were starved for three days and then refed for two days with either an elemental diet (Flexical); Flexical plus 30% kaolin; or Flexical plus 30% of a fibre mixture. Cell production was determined by the accumulation of vincristine arrested metaphases in microdissected crypts. There was no significant difference between refeeding the rats with an elemental diet alone or with kaolin supplementation, however, the addition of fibre in CV rats was associated with a significant increase in intestinal crypt cell production rate in both the small intestine (p less than 0.01) and the colon (p less than 0.001). This marked proliferative effects of fibre was abolished in the GF rats. It can be concluded that it is the products of hind gut fermentation, not fibre per se that stimulate intestinal epithelial cell proliferation in the colon and small intestine.