Immune-enhancing enteral diet selectively augments ileal blood flow in the rat

Clinical studies show that immune-enhancing enteral diets (IED; with L-arginine, fish oil, and RNA fragments) decrease the rate of sepsis and shorten the length of hospital stay after the start of enteral feeding. These beneficial effects are dependent on the route of administration (enteral vs parenteral) and on the nutrient composition (IED vs standard diets). Gut exposure to an IED seems to preserve and/or augment intestinal mucosal immunity. However, nutrient absorption stimulates gut blood flow in a nutrient-specific manner (i.e., postprandial hyperemia). We hypothesized that an IED would initiate a different pattern of whole organ blood flow compared to a standard diet. This suggests that a mechanism for the protective effect of IED might be the preferential augmentation of gut blood flow to gut-associated lymphoid tissue (GALT) or mucosa-associated lymphoid tissue (MALT).

Male Sprague-Dawley rats (200-225 g) were anesthetized and cannulated for colorimetric microsphere determination of blood flow distribution (with the phantom organ technique). Animals received gastric gavage (2 ml) of an IED (Impact; Novartis) or an isocaloric, isonitrogenous control diet (Boost; Mead-Johnson). Blood flow to the antrum, duodenum, jejunum, ileum, colon, liver, kidneys, and spleen was determined at baseline and 30, 60, 90, and 120 min after gavage.

Baseline blood flows to the left and right kidneys were within 10%, indicating the technical integrity of the microsphere technique and assay. Control diet augmented blood flow compared to IED in the antrum, duodenum, jejunum, and spleen. Conversely, IED gavage stimulated a delayed and sustained hyperemic response in the ileum. IED also increased hepatic blood flow early (30 min). IED increased blood glucose levels compared to control diet at 30, 60, and 90 min, suggesting enhanced nutrient absorption.

These data show that blood flow distribution depends on nutrient composition and that IED preferentially augments blood flow to the ileum. Since the terminal jejunum and ileum contain much of the GALT, our data suggest that a mechanism for enterally stimulated mucosal immunity involves selective perfusion of the terminal ileum during IED nutrient absorption.