DO ENFLURANE AND ISOFLURANE INTERFERE WITH THE RELEASE, ACTION, OR STABILITY OF ENDOTHELIUM-DERIVED RELAXING FACTORS

Purpose: The volatile anaesthetics enflurane and isoflurane inhibit th e endothelium dependent-relaxation in some in vitro preparations, To d etermine their site of action on the endothelium-derived relaxing fact or/nitric oxide (EDRF/NO) pathway, experiments were conducted in a bio assay system. Method: Continuously perfused cultured bovine aortic end othelial cells (BAEC) were the source of EDRF/NO while a phenylephrine -precontracted denuded rabbit aortic ring, directly superfused by the BAEC effluent served to detect EDRF/NO. The effect of basal and bradyk inin(Bk)-stimulated EDRF/NO release on vascular tension was measured. The effect of 4% enflurane or 2% isoflurane on EDRF/NO-induced relaxat ion was determined. Results: Enflurane added to the perfusate either u pstream or downstream in relation to BAEC attenuated the relaxation in duced by Bk at low concentrations. On the other hand, isoflurane, adde d either upstream or downstream to BAEC, potentiated the relaxation in duced by the basal release of EDRF but attenuated the relaxation induc ed by the Bk stimulated release of EDRF. Neither enflurane nor isoflur ane attenuated the relaxation induced by sodium nitroprusside (SNP), a n NO donor Conclusion: Enflurane decreases the stability of EDRF/NO re leased after Bk stimulation while isoflurane can have opposite effects depending on whether the relaxation results from basal or Bk-stimulat ed release of endothelial derived relaxing factor(s). Isoflurane incre ases the stability or action of the basal relaxing factor decreases th e stability of the Bk-stimulated relaxing factor (which is probably NO ).