Does halothane interfere with the release, action, or stability of endothelium-derived relaxing factor/nitric oxide?

Background: Halothane attenuates endothelium-dependent relaxation. To differentiate halothane's effect on endothelium-derived relaxing factor/nitric oxide (EDRF/NO) production from its effect on nitric oxide action on vascular smooth muscle, halothane's effect on endothelium-dependent relaxation was studied in a bioassay system.

Methods: Indomethacin-treated, bovine aortic endothelial cells (BAEC) grown on microcarrier beads, continuously perfused by oxygenated and carbonated (95% O2, 5% CO2) Krebs-Ringer solution served as nitric oxide donors while an isolated denuded rabbit aortic ring directly superfused by the effluent of the BAEC and precontracted with phenylephrine was used to detect EDRF/NO release. The effect of basal and bradykinin-stimulated EDRF release on the tension of the vascular ring was measured. In the bioassay, it was possible to treat either the vascular denuded ring alone or the vascular ring plus the BAEC with halothane by adding it to the perfusate either upstream or downstream from the BAEC. Halothane (final concentration 2.2%) was added to the perfusate at these two positions, and its effect on the relaxation induced by EDRF/NO was determined. In some experiments, the preparations were treated with hemoglobin or L-monomethyl-L-arginine to attenuate the relaxation induced by the EDRF/NO pathway. Finally, halothane's effect on vascular relaxation induced by an increasing concentration of sodium nitroprusside was measured. Halothane's concentration in the perfusate was determined by gas chromatography using electron capture for anesthetic measurement.

Results: EDRF/NO released by the BAEC was responsible for the relaxation of the vascular ring. Halothane added to the perfusate potentiated the tension induced by phenylephrine (7.1 +/- 1.89%) and attenuated the relaxation induced by the release of EDRF/NO. This effect was reversible after discontinuation of halothane. Halothane's effect was present even when the anesthetic was added to the perfusate downstream to the perfusion of the endothelial cells. Halothane had no effect on the vascular relaxation induced by sodium nitroprusside.

Conclusions: The authors' data demonstrate that halothane does not interfere with endothelial cell release of EDRF/NO and its smooth muscle cell relaxation but seems to modify either EDRF/NO half-life or its activated redox form.