Inhibitory Effects of Etomidate and Ketamine on Adenosine Triphosphate–Sensitive Potassium Channel Relaxation in Canine Pulmonary Artery

BACKGROUND: The authors recently demonstrated that etomidate and ketamine attenuated endothelium-dependent pulmonary vasorelaxation mediated by nitric oxide and Ca -activated K + channels. In the current study, they tested the hypothesis that these intravenous anesthetics inhibit pulmonary vasorelaxation mediated by adenosine triphosphate-sensitive potassium (K + ATP ) channel activation. METHODS: Endothelium intact and denuded pulmonary arterial rings were suspended in organ chambers for isometric tension recording. The effects of etomidate (5 x 10(-6) and 5 x 10(-5) m) and ketamine (5 x 10(-5) and 10(-4) m) on vasorelaxation responses to lemakalim (K + ATP channel activator), prostacyclin, and papaverine were assessed in phenylephrine-precontracted rings. The effect of cyclooxygenase inhibition with indomethacin was assessed in some protocols. RESULTS: Etomidate (5 x 10(-6) m) only inhibited the vasorelaxant response to lemakalim in endothelium intact rings, whereas a higher concentration of etomidate (5 x 10(-5) m) inhibited relaxation in both intact and endothelium-denuded rings. Pretreatment with indomethacin abolished the endothelium-dependent attenuation of lemakalim-induced relaxation caused by etomidate. Ketamine (5 x 10(-5) and 10(-5) m) inhibited the relaxation response to lemakalim to the same extent in both endothelium-intact and -denuded rings, and this effect was not prevented by indomethacin pretreatment. Etomidate and ketamine had no effect on the relaxation responses to prostacyclin or papaverine. CONCLUSIONS: These results indicate that etomidate, but not ketamine, attenuates the endothelium-dependent component of lemakalim-induced pulmonary vasorelaxation an inhibitory effect on the cyclooxygenase pathway. Both anesthetics inhibit K + ATP -mediated pulmonary vasorelaxation a direct effect on pulmonary vascular smooth muscle.