Rate of perfusion modulates colloidal carbon leakage from rat intestinal microvessels in vitro

In order to investigate the effects of varying the rate of flow on endothelial integrity the rat isolated small intestinal vasculature was perfused at 1, 5, 10 or 20 ml/min with a gelatin-containing physiological salt solution (GPSS), followed by an injection of colloidal carbon suspension (CC). Significantly greater microvascular CC leakage occurred at 1 or 5 ml/min than at 10 or 20 ml/ mitt. CC leakage at the two slower rates of flow was reduced by adding red blood cells to the GPSS, suggesting that the microvascular endothelium became hypoxic when perfused with GPSS at 1 or 5 ml/min. After perfusion at 20 ml/min with GPSS containing resiniferatoxin (1 muM) or 5-hydroxytryptamine (100 muM), CC leakage was significantly lower than after similar perfusion at 10 ml/min. Two nitric oxide (NO) synthesis blockers, N-nitro-L-arginine methyl ester (L-NAME, 100 muM) and methylene blue (20 muM), and an NO scavenger CPTIO (100 muM) each increased CC leakage. This suggests that NO was being produced at perfusion rates of 10 or 20 ml/min. Sodium nitroprusside (10 muM), 8-bromo-cGMP (100 muM) and BN52021 (10 muM) each significantly reduced CC leakage in the presence of L-NAME.