Metabolic responses to enteral and parenteral nutrition

Seven pairs of rats were simultaneously infused with a chemically formulated nutritionally complete amino acid-glucose diet which was delivered, at the same rate, into a central vein or into a feeding gastrostomy. The intragastrically infused rats showed greater weight gain than did the intravenously infused rats. This could not be explained by fluid retention since intake and output were similar in the two groups of animals. There was a greater increase in serum immunoreactive insulin (IRI) at day 8 in the intragastrically infused animals, but a smaller increment in serum immunoreactive pancreatic glucagon (IRG) at that point. Levels of enteroglucagon or glucagon-like immunoreactivity (GLI) were maintained in the intragastrically infused rats but declined markedly in the intravenously infused rats. It is possible that the greater release of IRI seen with the intragastric amino acid-glucose feeding contributes to better disposal of nutrients and greater weight gain. The presence of nutrients in the intestinal lumen may have stimulated the release of GLI, which in turn is insulinotropic.