Chronic ursodeoxycholic acid- and chenodeoxycholic acid-feeding-induced changes of colon mucosal cell proliferation in rats.

Hyperproliferation has been suggested to play a major role in bile acid-dependent colorectal tumor promotion. Effects of chronic feeding of chenodeoxycholic acid (CDC) and ursodeoxycholic acid (UDC) were tested on cell proliferation in the colon of male noninbred Wistar rats. By use of a dynamic method measuring actual rates of cell production, proliferation was modulated by both bile acids only in the proximal part of the colon. UDC feeding produced mild hyperproliferation of basal crypt cells (cell position 5-8: 7.6 +/- 2.0 vs. 3.5 +/- 1.3 cells/1,000 cells/hr--P less than .05; cell position 9-12: 18.1 +/- 10.7 vs. 10.3 +/- 2.9--P less than .05; cell position 13-16: 18.1 +/- 8.9 vs. 9.1 +/- 2.3--P less than .05). This finding reflected a characteristic compensatory response to superficial cell damage. However, CDC application did not effect cell regeneration in this crypt area but led to a striking drop of cell renewal in higher crypt cell positions (positions greater than or equal to 17), where no proliferation was detectable. These data suggest that CDC exerts its tumor-promoting effect by other means than hyperproliferation.