Adaptation of intestinal muscle in continuity after jejunoileal bypass in the rat.

Functional and structural adaptations of the intestine that remained in continuity after jejunoileal bypass [the in-continuity (IC) segment] were characterized in the rat. Three days after bypass, transit was rapid in fed rats, but, by 35 days, transit had slowed to mimic that seen in the intact intestine of control animals. In fasted rats, transit was as rapid as in the fed animals at 3 days after bypass; however, in fasted rats, transit did not slow when tested up to 35 days after operation. Transit in animals at 3, 14, and 35 days after sham operation was not different from control. Mucosal weights in the proximal and distal portions of the IC segment were increased at 3, 14, and 35 days after bypass. The wet weights and protein contents of the muscle and serosal layers of both portions of the IC segment were increased at 35 days. These findings support the hypothesis that the adaptation seen in the IC segment after bypass involves changes in function and structure of the intestinal smooth muscle as well as the intestinal mucosa.