Gastrointestinal response to oral versus gastric feeding of defined formula diets

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Abstract
The gastrointestinal response in rats nourished by continuous intragastric infusion of a variety of defined formula diets was compared with animals consuming the same diets orally. Two groups of rats were fed isocaloric amounts of DFD (73 kcal/day); group 1: sham-operated, orally-fed; group 2: operated, intragastrically-fed. Diets included; Vivonex (V), Flexical (F), Vital, Vivonex high nitrogen, and a control casein rat liquid formula diet (C). After 2 wk rats were killed and the liver, pancreas, and small bowel removed. The bowel was divided into eight equal segments. Mucosal weight, DNA, and protein concentration per cm segment were measured. Pancreatic amylase activity (units/g), and liver weight and lipid content were measured. Weight gain was comparable in all oral-fed groups, but was decreased in all gastric-fed animals compared to the oral-fed group. Nitrogen retention was not influenced by route of feeding but was significantly lower for Vivonex and Flexical animals (p < 0.01) in both oral-fed and gastric-fed groups. There was significant accumulation of lipid in the liver of both oral-fed and gastric-fed animals sustained on Vivonex and Vivonex high nitrogen (p < 0.01). Most proximal intestinal segment weight and mucosal weight, protein and DNA were decreased compared to the control diet in both oral-fed and gastric-fed animals. These studies demonstrate that while the gastrointestinal response to isocaloric defined formula diets was significantly influenced by the specific diet, fewer responses were modified by feeding defined formula diets orally versus gastrically.