Maintenance of gut mass in bypassed bowel of orally vs parenterally nourished rats

Abstract

Twenty-six male rats (experimental) underwent bypass of more than 70% of their small bowel, and nine rats underwent small bowel transection and reanastomosis. Rats were fed standard laboratory chow for the initial 18 postoperative days and then were switched to an elemental nutrient solution consisting of amino acids, glucose, vitamins, and minerals, either orally or parenterally (TPN) for the next 10 to 13 days. At the end of the experiment, in continuity and bypassed segments from both parenterally and orally fed animals were compared to each other and to similar segments of bowel from control rats. Our data indicate that oral intake and/or digestion and absorption of nutrients by the in continuity alimentary tract provides a stimulus to hyperplasia in the in continuity small bowel and a systemic stimulus that permits maintenance of gut mass in large bypassed segments of small bowel. Such a systemic stimulus is absent when the rat is provided TPN. Bypassed rats, remaining on oral nutrition throughout the 28- to 31-day postoperative period, had bypassed segments that maintained bowel weight, mucosal protein and RNA and DNA content similar to comparable segments of control bowel, while bypassed bowel from the TPN group underwent atrophy. The systemic stimulus does not appear to be gastrin since serum and antral gastrin levels were similar in bypassed and control rats and serum levels were consistent with previously determined fasting gastrin levels.