|Budget Amount *help
¥2,000,000 (Direct Cost : ¥2,000,000)
Fiscal Year 1999 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 1998 : ¥1,200,000 (Direct Cost : ¥1,200,000)
Elevation of intracellular CaィイD12+ィエD1 level is and essential requisite for endothelial nitric oxide (NO) synthesis. As one of these pathways, it has been reported that the depletion of CaィイD12+ィエD1 in endoplasmic reticulum (ER) activated microsomal cytochrome P450 mono-oxygenase (P450 MO) and induces the biosynthesis of 5, 6-eopoxyeicosatrienoic acid (5, 6-EET), which in turn promote CaィイD12+ィエD1 influx from extracelluar fluids. Thapsigargin is one of the agents to induce this pathway. Volatile anesthetics have been demonstrated inhibit P450 MO activity in liver. However, little is known about their effects on vascular smooth muscle relaxation mediated though P450 MO in endothelium. The purpose of this study was to examine the effects of volatile anesthetics on endothelial P450 MO-mediated vasodilation.
With institutional approval, rings with endothelium from isolated rat thoracic aorta were suspended under a resting tension of 3.0 g in Krebs' bicarbonate solution. The rings were prec
ontracted with phenylephrine (3X10ィイD1-7ィエD1M ) and the relaxant effect of thapsigargin (10ィイD1-7ィエD1 to 10ィイD1-6ィエD1 M), which depletes CaィイD12+ィエD1 in ER, and that of 5, 6-EET (5X10ィイD1-6ィエD1 M) were tested in the presence or absence of volatile anesthetics (Halothane, Isoflurane, and Sevoflurane, 1 to 3 MAC in human). Thapsigargin-induced relaxation was also tested in the presence or absence of pretreatment with inhibitors, which were econazole (P450 MO inhibitor, 2X10ィイD1-5ィエD1 M) and NィイD1GィエD1-nitro-L-arginine (L-NA, 10ィイD1-5ィエD1 M).
Thapsigargin caused a concentration-dependent relaxation, and that at 10ィイD1-6ィエD1 M was compatible with 5, 6-EET (5X10ィイD1-6ィエD1 M)-induced relaxation. Removal of endothelium or pretreatment with L-NA attenuated thapsigargin-induced relaxation significantly. The pretreatment with econazole also inhibited it significantly. Thapsigargin-induced relaxation was attenuated by Hal, Iso, and Sevo (1 to 3MAC) in a concentration-dependent manner. The potency of inhibitory effect of anesthetics on thapsigargin-induced relaxation was ranked as Hal > Iso > Sevo at 3 MAC. Relaxation induced by 5, 6-EET was not influenced by volatile anesthetics. The results of the current study confirm that thapsigargin-induced vasodilation is NO-dependent and regulated by endothelial P450 MO. It is indicated that volatile anesthetics attenuate endothelium-dependent vasodilation mediated via the CaィイD12+ィエD1 depletion in ER-induced CaィイD12+ィエD1 influx, and 3) this attenuation is mediated by the inhibition of P450 MO in endothelium by anesthetics.