Development of a chronic canine model for measurement of absorption by substrate appearance in portal venous blood.

Research in absorption physiology requires animal models which closely resemble the in vivo situation. The description of a new canine model satisfying these requirements is the objective of this report. Dogs were instrumented with indwelling portal vein and carotid artery catheters, a catheter jejunostomy and an electromagnetic flow measuring probe around the portal vein enabling continuous flow recordings. Following intrajejunal infusion of nutritive substrates in the conscious animal, absorption was measured as the product of porto-arterial substrate difference and portal venous flow. The model was validated in five mongrel dogs: (1) Catheters and flow measuring device function over several months. (2) The sensitivity of the method was evaluated following intrajejunal infusion of l-glycine-l-tyrosine and its constituent amino acids. A significant portoarterial concentration difference of both amino acids enabling quantitative measurement of absorption resulted when the peptide was infused at 4 mmoles/hour (20 mM solution, 200 ml/h). (3) Infusion of complete nutritive formulas caused a significant increase in portal venous flow whereas neither saline nor the amino acids or the peptides investigated had a comparable effect. (4) A validation experiment by implantation of a second flow probe distal to the chronically implanted device provided evidence that granulomatous tissue forming around the probe does not alter the accuracy of the flow recording. In summary, this method permits for the first time quantitative measurement of absorption by appearance rates in portal venous blood instead of by disappearance from the intestinal lumen.