Adaptation of intestinal muscle in bypassed loops after jejunoileal bypass in rat

The function and structure of intestinal smooth muscle in the bypassed intestine of rats with 70% intestinal bypass were compared with the function and structure of muscle from equivalent areas of intestine from transected and nontransected controls. Muscle function was assessed by evaluating changes in intestinal transit. At all times studied after operation, transit in transected controls was identical to that seen in nontransected controls. In the bypassed intestine at 3 days after operation, transit in fasted animals was significantly slower than intestinal transit in either control group. Over a period of 14-35 days, transit in the bypassed intestine of fasted animals returned toward control values. In fed animals, on the other hand, transit was delayed when measured at both 3 and 35 days after bypass operation. These findings demonstrate a persistent change in muscle function in bypassed intestine in response to the ingestion of a meal. No changes in intestinal structure were found when bypassed intestine was compared with tissue from transected controls. Thus there were no indications of mucosal or muscular atrophy in the bypassed intestine. The weights of the combined submucosal, muscular, and serosal layers in the study segments were increased at 35 days after either bypass or transection compared with tissue from nontransected controls. These changes appear to be a nonspecific result of operation.