Detection of early neoplastic changes in experimentally induced colorectal cancer using scanning electron microscopy and cell kinetic studies.

Abstract

SUMMARY Colonic tumours were induced in Wistar rats using 12 consecutive subcutaneous injections of azoxymethane at a dose of 10 mg/kg/week. Pairs of rats were killed at five weekly intervals after initial injection until 25 weeks. Colonic mucosa was sampled from five standard areas along the length of the colon and examined by both scanning electron microscopy and conventional light microscopy. The crypt cell production rate was measured by stathmokinetic techniques. Scanning electron microscopy showed microadenomas as early as five weeks and consistently after 15 weeks. They were found predominantly in the distal colon and increased in size with time. The lesions showed a progressive increase in the number of crypts per adenoma and increasingly disorganised slit shaped crypt orifices. The presence of epithelial dysplasia in the microadenomas and of invasion of the colonic wall by carcinoma was confirmed histologically, although fewer lesions were identified in tissue sections than by scanning electron microscopy. Crypt cell production rate increased with time, particularly in the distal colon. This increase was significant between five and 25 weeks. The results of these observations suggest that there is an adenoma-carcinoma sequence in this animal model. The value of scanning electron microscopy in identifying and quantifying the mucosal changes during carcinogenesis is emphasised.

The effects of intracolonic EGF on mucosal growth and experimental carcinogenesis

“…In our study, the colonic CCPRs of the groups treated with rectally administered saline were similar to previously reported values in both the carcinogen treated and control animals (Cooke et al, 1984). The stimulatory effect of the carcinogen was not seen at the 10 cm position in this study; indeed, azoxymethane is known to produce a range of responses throughout the colon (Cooke et al, 1984).…”

“…The stimulatory effect of the carcinogen was not seen at the 10 cm position in this study; indeed, azoxymethane is known to produce a range of responses throughout the colon (Cooke et al, 1984). The higher dose of EGF caused a significant stimulation of mucosal growth at the 5 cm sampling site in the control animals when compared to the animals receiving the lower dose.…”

Changes in crypt cell DNA content during experimental colonic carcinogenesis

“…Using the same animal model, we have found that during carcinogenesis there is an increase in the crypt cell production rate in the descending colon (Cooke et al, 1984). This leads to an increase in the size of the proliferative compartment and to an increase in the mean cellular DNA content in the middle of the crypts.…”

“…In adenomas, which in this model are believed to be premalignant lesions (Cooke et al, 1984), the mean cellular DNA levels are the same throughout the length of the crypts indicating that all of these cells have the same reproductive capacity. It is also possible that some of these polyps are composed of clones of aneuploid cells.…”

“…Colonic crypts have an orderly kinetic organisation, changes in which can be detected using stathmokinetic or thymidine labelling techniques (Cooke et al, 1984;Wright & Allison, 1984). An alteration of the kinetic organisation of the crypts is seen in patients with polyposis coli and ulcerative colitis with an increase in the size of the proliferative compartment (Bleiberg et al, 1972;Eastwood & Trier, 1973;Lipkin, 1977).…”