Background: The mechanism of isoflurane-induced cerebral hyperemia is poorly understood. Data from studies in vitro suggest that volatile anesthetics release a vasodilator prostanold. We hypothesized that prostanoids and nitric oxide (NO) are mediators of this response in vivo. If true, inhibition of cyclooxygenase by indomethacln (5 mg/kg intravenously) or of nitric oxide synthase by N(R)-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg intravenously) should attenuate isoflurane-induced hyperemia. Any response to L-NAME occurring via nitric oxide should be competitively reversed by L-arginine.
Methods: The cerebral blood flow (microsphere) response to 1 MAC isofiurane was tested at three time points (0, 90, and 180 min) in pentobarbltal-anesthetized pigs. Isofiurane challenges were separated by 60-min periods of continuous intravenous pentobarbital alone. Control animals (n = 7) received no additional pharmacologlc intervention. Experimental animals were randomized to receive L-NAME before the second and indomethacin before the third isofiurane challenge (n = 7); L-NAME before the second and L-arginine (400 mg/kg intravenously) before the third isofiurane challenge (n = 9); or indomethacin before the second and L-NAME before the third isofiurane challenge (n = 8).
Results: In control animals, isofiurane reproducibly increased cerebral blood flow (whole brain; 113 +/- 18%, 120 +/- 18%, and 103 +/- 19% increase above baseline at each time point, respectively). Both indomethacin and L-NAME attenuated (10 +/- 10% and 52 +/- 11% increase, respectively) the hyperemic response to isofiurane. The effect of L-NAME was reversed by L-arginine.
Conclusions: We conclude that both prostanoids and nitric oxide contribute to isoflurane-induced hyperemia. We are unable to determine from our data what, if any, interaction exists between these two mechanisms.
(C) 1994 American Society of Anesthesiologists, Inc.