VOLATILE ANESTHETIC ACTIONS ON NOREPINEPHRINE-INDUCED CONTRACTION OF SMALL SPLANCHNIC RESISTANCE ARTERIES

The aim of this study was to investigate volatile anaesthetic action on small splanchnic resistance arteries. Employing isometric tension recording, we studied the effects of clinically relevant concentrations (0.25-1.25 minimum alveolar concentration (MAC)) of isoflurane, sevoflurane and enflurane on contractions induced by norepinephrine (NE) a sympathetic neurotransmitter, in the rabbit small mesenteric artery. Rhythmic oscillations were observed in contractile responses to NE. Both isoflurane (greater than or equal to 0.25 MAC, 0.5% (approximate to 0.11 mM)) and sevoflurane (greater than or equal to 0.75 MAC, 2.8% (approximate to 0.38 mM)) inhibited the NE (10 mu M)-induced contraction with concomitant inhibition of average amplitude of the oscillations. Only enflurane (greater than or equal to 0.25 MAC, 0.7% (approximate to 0.20 mM)) generated vasoconstriction superimposed on the NE-induced contraction; however the vasoconstriction was transient and was followed by vasorelaxation. Concurrently, enflurane (greater than or equal to 0.25 MAC) strongly inhibited the average amplitude of the oscillations; higher concentrations (greater than or equal to 1.0 MAC) of enflurane completely eliminated the oscillations. The frequency of the NE-induced oscillations was less affected by the anaesthetics. The observed vasodilator action of these anaesthetics in small resistance arteries may contribute to their hypotensive effects in vivo. The potent inhibition of the rhythmic oscillations also may play a role in volatile anaesthetic-induced alterations in cardiovascular homeostasis.