Control of intestinal epithelial replacement: lack of evidence for a tissue-specific blood-borne factor

The small intestine of rats was cut across in 2 places, about 14 and 50% of the length of the small intestine from the pylorus, and continuity was reestablished by suturing the proximal and distal ends. The resulting sac of small intestine, averaging 36% of the total length of the small intestine, had its upper end closed off, and its lower end anastomosed, either to the intestine in continuity (an 'intestine sac'), or to the skin of the abdominal wall (a 'skin sac'). On the 9th post operative day, the cell production rate in squashes of microdissected whole crypts of Lieberkuhn was measured by mitotic blockade with Colcemid. The rate of cell production in unoperated and sham operated rats was 30 cells/crypt/hr, throughout the length of the small intestine. In the intestine in continuity, the rate increased to an average of 46 cells/crypt/hr above the anastomosis, and to 54 cells/crypt/hr below it. At the lower end of the 'intestine sac', which drained into the intestine in continuity, the rate was 39 cells/crypt/hr, while in the lower end of the sac which drained to skin the rate of cell production was only 16 cells/crypt/hr. This significantly lower cell production rate in intestine which was not in contact with ingesta is taken to be evidence of the importance of local, rather than blood borne factors in the control of epithelial replacement.