Enteral glutamine supplementation impairs intestinal blood flow in rats

Background: Clinical studies have shown that enteral immune-enhancing diets (IEDs) containing l-glutamine decrease septic complications and length of stay in some patient populations. Animal studies suggest IED benefits might include augmented gut blood flow. We hypothesized that enteral glutamine supplementation modulates gastrointestinal blood flow. Methods: Blood flow was measured in male Sprague-Dawley rats via the colorimetric microsphere technique at baseline, 60, and 120 minutes. Four groups were studied: (1) control diet (CD) + enteral glutamine; (2) CD + enteral glycine; (3) CD + enteral saline; and (4) CD + intravenous glutamine. Results: There were no differences in blood pressure or heart rate in any group. Group 1 blood flow was decreased at 120 minutes compared with controls (groups 2 and 3) in small intestine, colon, spleen, and pancreas, whereas the intravenous glutamine group (group 4) had no effect on blood flow. Conclusions: Enteral glutamine supplementation (as in IEDs) appears to impair gastrointestinal blood flow. Because glutamine provides energy directly to active enterocytes, enteral glutamine availability might diminish metabolic stimuli of absorptive hyperemia. This finding might partially explain the benefits observed with parenteral versus enteral glutamine supplementation in clinical studies (such as bone-marrow-transplant patients).