Short term infusion of glycine-extended gastrin17 stimulates both proliferation and formation of aberrant crypt foci in rat colonic mucosa

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Abstract
Evidence is accumulating that gastrin precursors may act as growth factors for the colonic mucosa in vivo and for colorectal carcinoma cell lines in vitro. The effect of short term administration of synthetic gastrins on the colonic mucosa in vivo, however, has not been reported. The aim of our study was to determine whether continuous systemic infusion of glycine‐extended gastrin17 stimulated proliferation and accelerated carcinogenesis in the colorectal mucosa. A significant increase in colonic mucosal proliferation as assessed by metaphase index was seen in the caecum (23%, p < 0.02) and distal colon (27%, p < 0.001), but not the rectum, after treatment of intact rats with glycine‐extended gastrin17 for 1 week using implanted miniosmotic pumps. Defunctioning of the rectum reduced both the proliferative index and crypt height of the rectal mucosa of untreated rats. Treatment of rectally defunctioned animals with glycine‐extended gastrin17 for either 1 or 4 weeks resulted in a significant increase in both the proliferative index (40% and 93%, respectively) and crypt height (11% and 19%, respectively) of the rectal mucosa. The total number of aberrant crypt foci in intact rats treated with the procarcinogen azoxymethane plus glycine‐extended gastrin17 was increased by 48% compared to the value in controls treated with azoxymethane only (p = 0.01). We conclude that short term administration of glycine‐extended gastrin17 to mature rats not only has a proliferative effect upon colonic mucosa, but also increases the number of aberrant crypt foci formed in the colorectal mucosa after treatment with azoxymethane. Glycine‐extended gastrin17 could thus potentially act as a promoter of carcinogenesis.