Kiyoshi Terasako

Mechanisms of inhibition of endothelium-dependent relaxation by halothane, isoflurane, and sevoflurane.

Volatile anaesthetics inhibit endothelium-dependent relaxation, but the underlying mechanism(s) have not been clarified. In an attempt to elucidate the mechanism(s), we determined the effects of halothane, isoflurane and sevoflurane on relaxation induced by acetylcholine and sodium nitro-prusside (SNP) and the cGMP formation elicited by exogenous nitric oxide (NO) and SNP in rat aortas. Acetylcholine (10−7−10−5M) - induced relaxation was attenuated by halothane (2%), isoflurane (2%) and sevoflurane (4%). SNP (10−8 M) - induced relaxation was reduced by halothane (2%), but not by isoflurane (2%) or sevoflurane (4%). The cGMP level of NO-stimulated aorta was reduced by halothane (2%) and sevoflurane (4%), but not by isoflurane (2%). The cGMP level of SNP (10−7 M) - stimulated aorta was reduced by halothane (2%), but not by isoflurane (2%) and sevoflurane (4%). We conclude that the mechanisms responsible for the inhibition of endothelium-dependent relaxation differ among anaesthetics. Isoflurane inhibits the relaxation mainly by inhibiting the formation of NO in the endothelium. In contrast, the effect of halothane on endotheliumdependent relaxation may be largely due to the inhibition of action of NO in the vascular smooth muscle and the effect of sevoflurane may be to inactivate NO or to inhibit the action of NO.RésuméLes agents anesthésiques volatils inhibent la relaxation d’origine endothéliale dont le mécanisme sous-jacent n’a pas été éclairci. Dans le but d’en élucider le(s) mécanisme(s), nous avons déterminé sur des aortes de rats les effets de l’halothane, de l’isoflurane et du sévoflurane sur la relaxation induite par l’acétylcholine et le nitroprussiate de sodium (SNP), et la synthèse de cGMP élicitée par l’oxyde nitrique (NO) et le SNP La relaxation induite par l’acétylcholine (10−7−10−5 M) est atténuée par l’halothane 2%, l’isoflurane 2% et le sévoflurane 4%. La relaxation induite par le SNP (10−8 M) est diminuée par l’halothane 2%, mais non par l’isoflurane 2% ou le sévoflurane 4%. Le niveau de cGMP de l’aorte stimulée par le NO est diminué par l’halothane 2% et le sévoflurane 4% mais non par l’isoflurane 2%. Le niveau de cGMP de l’aorte stimulée par le SNP (10−7) est diminué par l’halothane 2%, mais non par l’isoflurane 2% et le sévoflurane 4%. Nous concluons que les mécanismes responsables de l’inhibition de la relaxation d’origine endothéliale different selon l’anesthésique. L’isoflurane inhibe la relaxation principalement en inhibiant la synthèse endothéliale de NO. Par contre, l’effet de l’halothane sur la relaxation d’origine endothéliale peut être en grande partie due à l’inhibition de l’activité du NO sur le muscle vasculaire lisse et l’effet du sévoflurane peut être dû à l’inactivation du NO ou à l’inhibition de l’activité du NO.

Modification of Endothelium-dependent Relaxation by Propofol, Ketamine, and Midazolam

Since volatile anesthetics, barbiturates, and local anesthetics have been reported to inhibit endothelium-dependent relaxation, we hypothesized that any drug with anesthetic action would suppress this relaxation. In the present study, using rat thoracic aortae, we attempted to determine whether nonbarbiturate intravenous anesthetics, including midazolam, propofol, and ketamine, suppress endothelium-dependent relaxation, and to clarify the mechanism(s) involved. Acetylcholine-induced, endothelium-dependent relaxation was significantly attenuated by propofol and ketamine, but was unaffected by midazolam. Sodium nitroprusside (SNP)-induced relaxation was attenuated by propofol, but not by midazolam or ketamine. The acetylcholine-stimulated 3 prime,5 prime-cyclic guanosine monophosphate (cGMP) level was reduced by pretreatment with propofol and ketamine but not by midazolam, and that stimulated by SNP was reduced by propofol but not by ketamine or midazolam. We conclude that propofol and ketamine suppress endothelium-dependent relaxation, whereas midazolam has no influence. Moreover, the suppressive effect of ketamine on endothelium-dependent relaxation is mediated by suppression of nitrous oxide (NO) formation, whereas that of propofol may be mediated at least partly by suppression of NO function. (Anesth Analg 1995;81:474-9)

Identification of the amino acid residues involved in selective agonist binding in the first extracellular loop of the δ- and μ-opioid receptors

Effects of amino acid substitutions in the first extracellular loop region of the β‐ and μ‐opioid receptors were examined. Substitution of lysine‐108 of the δ‐receptor (δK108) with asparagine improved affinity to [d‐Ala2,MePhe4,Gly‐ol5]enk ephalin (DAGO), a μ‐selective peptide agonist, to be comparable with that of the μ‐receptor. On the other hand, replacement of mN127 with lysine decreased the affinity to DAGO by ∼ 15‐fold. These results suggest that dK108 and mN127, which correspond to each other in the aligned amino acid sequences, mainly determine the difference in DAGO binding affinity between the δ‐ and μ‐receptors.

Halothane and Enflurane Constrict Canine Mesenteric Arteries by Releasing Ca2+ from Intracellular Ca2+ Stores

Background:Recent studies suggest that volatile anesthetics cause not only vasodilation but also vasoconstriction, depending on the experimental conditions. However, the mechanism of the constrictive effect of volatile anesthetics has not been clarified. The aim of this study was to evaluate the vasoconstrictor effects of halothane, enflurane, and isoflurane and to elucidate the underlying mechanism. Methods:Vascular rings of canine mesenteric arteries were mounted in organ baths, and isometric tension changes were recorded. Changes in intracellular free Ca2+ concentration of vascular smooth muscle were examined by using the fluorescent Ca2+ indicator fura 2 and a dual-wavelength fluorometer. Results:Halothane (0.75–2.3%) and enflurane (1.7–3.4%), but not isoflurane (1.2–3.5%), induced a concentration-dependent transient contraction, followed by a slight, sustained contraction. Halothane (1.5%)- and enflurane (3.4%)-induced contractions were reduced by endothelial denudation and enhanced by indomethacin (10-5 M) treatment but were not affected by L-NG-nitroarginine (10-5 m) or nifedipine (2 X 10-7 M) treatment. Ryanodine (2 X 10-5 M) treatment completely abolished the transient increases in tension and Ca2+ concentration. Even in ryanodine-treated arteries, however, both anesthetics induced a slowly developing sustained contraction, and the sustained contraction induced by enflurane (3.4%) was not accompanied by a significant increase in Ca2+ concentration. Conclusions:Halothane and enflurane, but not isoflurane, induce vasoconstriction by releasing Ca2+ from intracellular stores. Release of a vasodilating prostanoid and endothelium-derived constricting factor may also be involved in the vasoconstrictor effect. Furthermore, increased Ca2+ sensitivity of contractile machinery may be involved in the effect of enflurane.