Figure 4. (A) Percentage relaxation of the U46619-preconstricted vessel in response to changes in pressure gradients (Delta P) across the vessel in the presence of different concentrations of isoflurane. Isoflurane attenuated Delta P-produced, flow-induced dilation in a concentration-dependent manner (P < 0.001). *P < 0.05 versus control. +P < 0.05 versus 1 minimum alveolar concentration (MAC) isoflurane. (B) Even after pretreatment of vessels with N (^{G-nitro-L-arginine})(L-NNA), 2 MAC isoflurane attenuated flow-induced dilation even further (P < 0.01), indicating that isoflurane attenuated dilation as a result of an L-NNA-insensitive agent, most likely a prostanoid. *P < 0.05 between vessels pretreated with L-NNA, whose flow-induced dilation was measured in the presence or absence of 2 MAC isoflurane. (C) Even after pretreatment of vessels with indomethacin, 2 MAC isoflurane attenuated flow-induced dilation even further (P < 0.05), indicating that isoflurane attenuated dilation because of an indomethacin-insensitive agent, most likely nitric oxide. *P < 0.05 between vessels pretreated with indomethacin. The flow-induced dilation of indomethacin was measured in the presence or absence of 2 MAC isoflurane.