The Effect And Mechanism Of Botulinum Toxin Type A On Rabbit Aortic Contractile-induced By Methoxamine And Electric Field Stimulation In Vitro

Backgrand:The inhibitive effect of botulinum toxin-A(BTX-A) is not only on cholinergic release in voluntary muscle,but also substance P(SP),vasoactive intestinal peptide (VIP),calcitonin gene-related peptide(CGRP) in smooth muscle and glands in our previous studies.Our proposals according to the previous study are that BTX-A might effect on sympathetic release in blood vessel and inhibits the contraction of blood vessel and promotes perfusion and oxygen of blood in tumor.The investigation of BTX-A as a adjuvant is a new approach to treatment of tumor.Objective:To investigate the inhibitory effect of BTX-A on rabbit aortic contractility-induced by methoxamine(MOA),an agonist of noradrenergicαreceptor,or electric field stimulation(EFS) in vitro,respectively.Methods:MOA-and EFS-treated group were carried out in this study.0.5×3.0 cm spiral-shaped strip of rabbit aorta was suspended in incubation bath containing Krebs bicarbonate buffer[composed of(in mM)120 NaCl,5.9 KCl,25 NaHCO₃,17.5 Dextrose,2.5 CaCl₂,1.2 MgCl₂,1.2 NaH₂PO4,(pH 7.4)],constant 37℃within oxygenated with 95% O₂-5%CO₂.one end of the strip was fixed to a hook on the bottom of the bath,the other end was connected to an isometric force transducer.These strips were suspended between platinum electrodes placed adjacent and parallel to the long axis of the aortic strips.Electrodes were connected to an electric stimulator.The aortic strips were prepared to 2g loading tension and equilibrate for 60minutes,and subdivided randomly into MOA group and EFS group.Strips in MOA-treated group were administrated MOA 5μM for promoting contraction for 30 min, followed the equal volume of vehicle(n=10),BTX-A 50 U(n=10) and 100 U/ml(n=10) respectively addition for 30 min recording,and subsequently treated with MOA 5μM again. Other strips in the EFS-treated group were stimulated by 50 Hz,80 V,1 ms and 60 s electricity,followed vehicle(n=10) and BTX-A 50 U/ml(n=10) respectively addition for 30 min,and subsequently treated with MOA 5μM again.The contractile graph in motility of the aortic strips were simultaneously recorded with physiological experimental system.Results:(1) BTX-A 50 U/ml and 100 U/ml decreased respectively 80%(P＜0.01) and 95%(P＜0.001) of the aortic contractile tension-induced by MOA.MOA repeated addition promoted respectively 35%(P＜0.001) and 3%(P＜0.001) of contractile tension of the strips-treated respectively with BTX-A 50 and 100 U/ml compared to the strips treated with Krebs solution.(2) BTX-A 50 U significantly reduced 94%(P＜0.001) of the aortic contractility-induced by EFS.MOA addition promoted only 10%(P＜0.001) of contractile tension of the strips treated with BTX-A 50 compared to the strips treated with Krebs solution.Conclusion:MOA and EFS promote rabbit aortic contraction.BTX-A inhibits respectively the contractile responses to MOA and EFS with a manner of dose-dependence through inhibiting noradrenergic release and receptor probably.