Abstract PR031

Abstract

Background & Objectives: The physiological mechanisms that regulate tissue blood flow sufficiently are involved in the control of endothelium-dependent vasodilation. Nitric oxide, which is produced by endothelial nitric oxide synthase (eNOS), acts as an endothelium-dependent vasodilator. eNOS activity is regulated by several mechanisms including intracellular calcium concentration ([Ca2+]i) and phosphorylation of eNOS. Phosphorylation of Ser1177 increases Ca2+ sensitivity of the enzyme (1). Endothelium-dependent vasodilation is impaired by sevoflurane (2). The interaction of desflurane locally with the action of endothelial cells remains unknown. This study was carried out to elucidate the effects of desflurane and sevoflurane on endothelium-dependent vasodilation and the mechanisms of regulation of eNOS activity. Materials & Methods: With institutional approval, a rat descending aorta with the endothelium was suspended in a temperature-controlled organ bath for measurement of isometric tension. Changes in tension in response to phenylephrine (3×10–7 M) followed by acetylcholine (10–6 M) were recorded in the presence or absence of desflurane (5.7%, 11.4%; 1, 2 MAC for normal rats) or sevoflurane (2.4%, 4.8%; 1, 2 MAC for normal rats) to test endothelium-dependent vasodilation. Cultured bovine aortic endothelial cells were treated with bradykinin (10–6 M) in the presence or absence of desflurane or sevoflurane (11.4% and 4.8%, respectively). After treatments, Western blotting was used to determine eNOS Ser1177 phosphorylation, and measurement of the fluorescence intensity of Fluo-3/AM, as a [Ca2+]i indicator, was used to study the changes of [Ca2+]i. Statistical analysis was performed using Kruskal-Wallis’ H-test followed by Newman-Keuls test for multiple comparisons. A P value < 0.05 was considered statistically significant. Results: Endothelium-dependent vasodilation of the rat aorta and production of NO was inhibited by both anesthetics. The inhibitory effect of desflurane was greater than that of sevoflurane (Figure 1A, 1B). Western blotting revealed that phosphorylation of eNOS Ser1177 was inhibited by sevoflurane but not by desflurane (Figure 1C). Live cell calcium imaging revealed that bradykinin-induced increase in [Ca2+]i was suppressed by desflurane but not by sevoflurane (Figure 1D).Conclusion: The findings suggest that sevoflurane inhibits endothelium-dependent vasodilation caused by inhibition of eNOS Ser1177 phosphorylation, whereas desflurane inhibits vasodilation by inhibition of calcium signal transduction of eNOS activity. This difference in inhibitory mechanisms might reflect the different degrees of inhibitory effects of sevoflurane and desflurane on endothelium-dependent vasodilation.