Reversal Of Lipid Emulsion On Bupivacaine Induced Vasculartoxicity On Isolated Rat Aorta As Well As Mechanisms

Bupivacaine(BUP) is a long-acting amide local anesthetic, with the feature of long duration of action and good effect of anesthesia, so it is widely used in clinical anesthesia such as epidural anesthesia, spinal anesthesia, brachial plexus block and so on. However, BUP also has certain adverse reactions, mainly in the central nervous system toxicity and cardiovascular toxicity, and the most obvious performance of the adverse reactions is cardiovascular toxicity. The cardiac toxicity of BUP mainly includes negative inotropic effect and negative conduction, such as PR interval and QRS prolongation, bradycardia, premature ventricular beats, ventricular tachycardia or ventricular fibrillation or even cardiac arrest. The effects of BUP on peripheral vascular are controversial. It has been reported that BUP induces vasoconstriction at low concentration and induces vasodilation at toxical concentration leading to occurrence of hypotension. However, the changes of vascular tension via different administration regimes of BUP and vasodilation induced by BUP in isolated rat aorta have not been clearly clarified. In addition, the regulations of BUP on different agonist-induced vasoconstriction still have not been reported. still have not been reported.BUP-induced toxicity can be reversed by lipid emulsion(LE) but the mechanism is still not clear. The use of LE to treat toxicity due to a highly lipophilic drug suggests the possibility of a “lipid sink” mechanism, where the offending agent is removed from affected tissues by partitioning into a plasma lipid phase created by the infusion. Meanwhile, LE contains essential fatty acid which is one of the indispensable energy metabolisms in the heart. Because of a certain activity of the cardiovascular system, LE may promote the recovery of myocardial function. In this study, therefore, we evaluated the effects of different ways of BUP administration on the tension in isolated rat aorta; BUP-induced vasodilations in the aorta precontraction with different vasoconstrictors were analysed. In addition, the time-dependent biphasic regulation of BUP on the vasoconstriction induced by α1-adrenoceptor agonist phenylephrine(Phe) and the reversal action of LE were investigated. At last, we analyzed the effects of BUP or LE on vasoconstriction induced by 5-hydroxytryptamine(5-HT) and Phe as well as vasodilation induced by acetylcholine(ACh). acetylcholine(ACh). Part Ⅰ Regulation of BUP on vascular tension in isolated rat aortaObjective: Isometric vasoconstrictive responses to BUP, administered by cumulavive manner or single concentration manner, were recorded in the rat aorta. BUP induced vasodilations were recorded after precontraction with Phe and KCl.Methods: The isolated rat aortic rings were prepared and suspended in an organ bath; vasoconstriction and vasodilation induced by different drugs were recorded. Results:1 Vasoconstriction to single and cumulative administration of BUP in the isolated rat aorta.BUP induced concentration-dependent vasoconstriction over the range of 10-300 μmol/L when administered either as single concentration or cumulatively. The maximal vasoconstrictions were 24.9±5.75% and 20.7±4.40% for single or cumulative administration, respectively, with no significant difference between the two administration types(P>0.05). As the concentration increased, the extent of BUP-induced vasoconstriction was significantly reduced. This effect was significantly larger during cumulative administration than during the administration of single concentrations; 500 μmol/L BUP induced vasoconstrictive responses of 6.4±10.34% and 15.0±5.40%, respectively(P<0.01). The vasoconstrictive responses(g) induced by KCl(60 mmol/L) in the seven groups treated with the two different types of BUP administration(single and cumulative) were not significantly different from each other(P>0.05). These vasoconstrictive responses were 2.44±0.27 g, 2.31±0.28 g, 2.29±0.53 g, 2.40±0.35 g, 2.33±0.46 g and 2.63±0.18 g in the single concentration groups and 2.20 ± 0.09 g in the cumulative concentration group. cumulative concentration group.2 Vasoconstrictive responses to three times of cumulative administration of BUP in the isolated rat aortaWhen BUP(10, 30, 100, and 300 μmol/L) was administered cumulatively three times, the second and third vasoconstrictive responses were significantly lower than the first vasoconstrictive response(P<0.05 and P<0.01). The vasoconstrictive responses to 300 μmol/L BUP were 0.35±0.15 g and 0.20±0.12 g during the second and third administrations, respectively, which were significantly lower than the first vasoconstrictive response(0.48±0.17 g; P<0.01). The third cumulative administration also induced a significantly lower vasoconstrictive response than did the second(P<0.01). The vasoconstrictive response induced by 60 mmol/L KCl was 1.50±0.19 g, which was significantly lower than that observed in the preparations exposed to BUP(single or cumulative groups)(P<0.01). Part Ⅱ Time-dependent biphasic regulation of BUP on α1-adrenoceptor-mediated vasoconstriction and reversal effect of LE in isolated rat aortaObjective: The time-dependent regulation of BUP on α1-adrenoceptor-mediated vasoconstriction was investigated in isolated rat aorta rings. If BUP inhibited the α1-adrenoceptor-mediated vasoconstriction, the reversal effect of LE on the inhibition of BUP was analyzed. In addition, the effects of BUP on 5-HT mediated vasoconstriction were also invenstigated.Methods: The isolated rat aortic rings were prepared and suspended in an organ bath; vasoconstriction and vasodilation induced by different drugs were recorded. Results:1 Effect of 20-min BUP pretreatment on Phe-induced vasoconstriction and ACh-induced vasodilationPrior to analyzing the effects of BUP(3, 10, 30, 100, and 300 μmol/L) on the aortic preparations, we confirmed that the preparations in the five different BUP concentration groups and the solvent control group showed no significant differences in their vasoconstrictive responses to Phe(0.0001–30 μmol/L) or their vasodilatory responses to ACh(0.0001-3 μmol/L)(P>0.05). The vasoconstrictive responses to Phe were enhanced after a 20-min pretreatment with BUP(3, 10, and 30 μmol/L) compared with the solvent control group(P<0.01), and the enhancement produced by 30 μmol/L BUP was significantly stronger than that produced by 3 μmol/L BUP(P<0.01). Compared with the solvent control group, the high concentration of BUP(300 μmol/L) significantly inhibited aortic vasoconstriction in response to Phe(P<0.01). After washing the preparations that were pretreated with BUP thoroughly, vasoconstrictive responses to Phe were still significantly lower than those observed in the control group(P<0.01). In addition, all of the groups pretreated with BUP at the concentrations of 3, 10, 30, 100, and 300 μmol/L showed significantly reduced vasodilatory responses to ACh compared with the solvent group(P<0.01), and the inhibition induced by 30, 100, and 300 μmol/L BUP was significantly greater than that induced by 3 μmol/L BUP(P<0.01).2 Effect of 40-min BUP pretreatment on Phe-induced vasoconstriction and ACh-induced vasodilationThe four BUP concentration groups and the solvent control group showed no significant differences in their vasoconstrictive responses to Phe(0.0001-30 μmol/L) or their vasodilatory responses to ACh(0.0001-3 μmol/L) before analyzing the effects of BUP(P>0.05). Vasoconstrictive responses to Phe were significantly reduced by 40-min pretreatment with BUP(3-300 μmol/L) compared with the solvent control group; this effect was concentration dependent(P<0.01). This inhibition persisted and was further enhanced after the preparations treated with 10 and 300 μmol/L BUP were washed thoroughly. In addition, the groups pretreated with 3, 10, and 300 μmol/L BUP showed significantly reduced vasodilatory responses to ACh compared with the control group(P<0.01), and the inhibitory effects of 10 and 300 μmol/L BUP were significantly stronger than those observed with 3 μmol/L BUP(P<0.01).3 Reversal effects by LE on the BUP-induced vascular toxicity 3 Reversal effects by LE on the BUP-induced vascular toxicityThere were no significant differences among the first vasoconstrictive concentration-response curves to Phe(0.0001-30 μmol/L) in the preparations prior to treatment with NS, NS+BUP, LE, and LE+BUP(P>0.05). For the vasoconstrictive responses to the second exposure to Phe in these four groups, the group treated with LE showed significantly greater vasoconstriction than did the NS group. Phe-induced vasoconstriction was increased by 23% at a concentration of 30 μmol/L(P<0.01). The vasoconstrictive response in the NS+BUP was significantly lower than that of the NS group; vasoconstriction to 30 μmol/L Phe was decreased by 21%(P<0.01). LE pretreatment(LE+BUP) was associated with recovery of the vasoconstrictive response to Phe(30 μmol/L) to the level recorded in the NS group(P>0.05). This LE-mediated enhancement of Phe-induced vasoconstriction was reduced after the preparations were washed repeatedly.The first vasodilatory concentration-response curve to ACh(0.0001-3 μmol/L) did not differ significantly between the groups prior to NS and NS + BUP treatment(P>0.05); however, ACh-induced vasodilation was weaker in the LE and LE + BUP groups compared with the NS group(P<0.01), and no difference was observed between the LE and LE+BUP groups. For the vasodilatory responses to the second ACh exposure in the 4 groups, the vasodilatory responses in preparations exposed to LE and NS+BUP were significantly decreased compared with the NS group(P<0.01), and the inhibition induced by NS+BUP was stronger than that observed in the LE group(P<0.05). The vasodilatory response to ACh was significantly lower in the LE+BUP group compared with the NS+BUP group(P<0.01).4 Effect of different LE concentrations on Phe-induced vasoconstriction and ACh-induced vasodilationThe vasoconstrictive response to Phe was not significantly altered following exposure to LE(0.2%-0.6%) for 5 min compared with the NS group(P>0.05). The negative Log EC50 of Phe-induced vasoconstriction increased from 7.32±0.17 in the NS group to 7.74±0.24 in the 0.8% LE group(P<0.01); however, the Emax was not significantly altered(P>0.05). For the vasoconstrictive responses to the second Phe exposure in the 5 groups, LE(0.2%-0.8%) not only increased the Emax of Phe-induced vasoconstriction significantly(P<0.01) but also increased the negative Log EC50(P<0.01). LE(0.6% and 0.8%) increased the negative Log EC50 of Phe-induced vasoconstriction significantly compared with 0.2% LE(P<0.05 and P<0.01, respectively).The vasodilatory response to ACh(0.0001-3 μmol/L) was decreased significantly by exposure of the aorta preparations to LE(0.2%-0.8%) for 5 min compared with exposure to NS(P<0.01). LE(0.8%) produced a significantly stronger reduction of ACh-induced vasodilation than 0.2% LE(P<0.01). LE-related inhibition of the ACh-induced vasodilatory response was further aggravated with the persistence of LE incubation. The maximal vasodilations observed after exposure to 0.2%, 0.4%, and 0.6% LE for 5 min were 70.57±6.22%, 62.70±6.82%, and 67.38±7.27%, respectively; these values were further decreased to 51.99±6.10%, 44.57±6.30%, and 45.47±4.70%, respectively 5 Effects of yohimbine and propranolol on Phe-induced vasoconstrictionThere were no significant differences in Phe-induced vasoconstriction in the two groups of preparations prior to the administration of yohimbine(0.3 μmol/L) and propranolol(1 μmol/L)(P>0.05). Blockade of the α2- and β-adrenoceptors by yohimbine and propranolol, produced no significant differences in the vasoconstrictive response to Phe compared with that observed in the solvent group(P>0.05). 6 Effect of 40-min BUP pretreatment on 5-HT-induced vasoconstrictionThe BUP group and the solvent control group preparations showed no significant differences in their vasoconstrictive responses to Phe(0.0001-30 μmol/L) before the treatment with BUP(P>0.05). There were also no significant differences about the vasoconstrictive responses to 5-HT(0.1-300 μmol/L) between the BUP group and solvent control group before administration of BUP(10 μmol/L). Vasoconstrictive responses to 5-HT were not influenced by 40-min pretreatment with BUP(10 μmol/L) compared with the solvent control group. Part Ⅲ Regulation of LE on vasoconstriction of isolated rat aortaObjective: We compared the enhancement of long time pretreatment with LE on α1-adrenoceptor agonist Phe-induced vasoconstriction in endothelium-intact or endothelium-denuded rat aorta.Methods: The isolated rat aortic rings were prepared and suspended in an organ bath; vasoconstrictions induced by different drugs were recorded.Results: Results: Prior to analyzPrior to analyzing the effect of 0.4% LE on the aortic preparations, we confirmed that the endothelium-intact+NS group and the endothelium-intact+LE group preparations showed no significant differences in their vasoconstrictive responses to Phe(0.0001-30 μmol/L)(P>0.05). There were also no significant differences about the vasoconstrictive responses to Phe(0.0001-30 μmol/L) between endothelium-denuded+NS group and endothelium-denuded+LE group(P>0.05). Compared endothelium-intact+NS and endothelium-intact+LE group with endothelium-denuded+NS and endothelium-denuded+LE group, Phe induced vasoconstrictions were significantly greater in endothelium-denuded preparations than endothelium-intact preparations, the vaules of Emax and negative Log EC50 were also significangtly increased(P<0.01).The vasoconstrictive responses to Phe were enhanced after a long time pretreatment with 0.4% LE in endothelium-intact+LE group compared with endothelium-intact+NS(P<0.05), the values of Emax were 2.72±0.35 and 2.23±0.23 g, respectively, with significant difference(P<0.01). The value of Emax was increased by 22% after pretreatment with LE in endothelium-intact rings. The vaules of negative Log EC50 were 6.93±0.30 and 6.58±0.21 mol/L, respectively, with significant difference(P<0.01). Compared with endothelium-denuded+NS group, the vasoconstrictive responses to Phe were significantly enhanced, the values of Emax were 2.53±0.21 and 2.82±0.22 g, respectively, with significant difference(P<0.01). The value of Emax was increased by 11% after pretreatment with LE in endothelium-denuded rings. The vaules of negative Log EC50 were 7.37±0.22 and 7.07±0.21 mol/L, respectively, with significant difference(P<0.01).Conclusion: Conclusion: The vasodilationThe vasodilation produced by cumulatively administration of BUP at high concentrations related to toxic plasma levels is significantly greater than single concentration administration in isolated rat aorta. BUP induced vasoconstriction is decreased significangtly and damages the vasoconstriction induced by high K+ after reduplicated administration.BUP produces different vasodilatory effects after precontraction with different vascular vasoconstrictors of Phe and KCl. The vasodilation of BUP is related to vascular smooth muscle rather than vascular endothelium.BUP, when exposed to isolated rat aortic rings, has two opposite effects on α1-adrenoceptor-mediated vasoconstriction—short-term exposure-related enhancement and long-term exposure-related inhibition. The clinical concentration of BUP has no effect on the vasoconstriction induced by 5-HT.LE can enhance the vaules of Emax and p D2 of α1-adrenoceptor agonist Phe-induced vasoconstriction after a long time exposure with preparations, thus reverses the inhibition of BUP on α1-adrenoceptor-mediated vasoconstriction. This enhancement of LE is more obvious in the endothelium-intact preparations. In addition, LE can significantly enhance vasoconstrictive response to 5-HT and increase the values of Emax and p D2 of endothelium-intact preparations.