How laboratory dogs accommodate meals of different size but similar composition.

Healthy laboratory dogs appear to absorb a mixed meal from the gut at a constant rate. This rate is apparently not affected by meal size. If this is the case, then duration of absorption should depend on total or integrated meal size, whereas metabolite and hormonal levels would be independent of the number of feedings. To explore these hypotheses further, we compared the metabolite and hormonal responses with a single mixed meal and one divided in two halves, provided in two feedings 4 h apart. We detected no effect of the second meal in the metabolic response levels of glucose, lactate, pyruvate, alanine, free fatty acids, or 3-hydroxybutyrate or the hormonal responses of insulin, pancretic glucagon, gastrin, or secretin. Only minor differences were detectable in the hormonal response levels of pancreatic polypeptide, gastric inhibitory peptide, and enteroglucagon, consistent with a response to a second meal. We conclude that the observed change in circulating metabolite or hormone concentration is independent of the size of meal eaten, but the duration of the excursion depends on meal size. Thus, during the bulk phase of nutrient uptake, the absorption mechanism of the laboratory dog appears to be saturated.