Inhibition of botulinum toxin A on rat duodenal smooth muscle in vitro

Objective To investigate whether botulinum toxin type A(BTX-A) inhibits spontaneous contractility of isolated duodenal smooth muscle and acetylcholine(ACh)-induced contractility,whether the inhibitory characteristics of BTX-A are the same manner with antagonists of muscarinic receptor.Pretreatment of duodenal smooth muscle with BTX-A,ACh administration still enhances the contractile response or not.The aim of this study is to demonstrate the efficiency of BTX-A to treat the disorder of intestinal function.Methods Sprague-Dawley rats were used in this study.Duodenal smooth muscle strip of 1.0 to 1.5 cm was quickly removed from distal pylori after the unconsciousness in the rats by hitting head.The smooth muscle strip was rinsed with Krebs bicarbonate buffer.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.Muscle strips were prepared to 1 g loading tension,and subdivided randomly into BTX-A group(n=12),atropine group(n=12),ACh + BTX-A group(n=12),ACh+atropine group(n=12),BTX-A + ACh group(n=12).The contractile graph in motility of the muscle strips was simultaneously recorded with physiological experimental system.Results BTX-A(10 U/ml) reduced the frequency,tension and amplitude of spontaneous contractility of duodenal smooth muscle compared to incubation in Kreb solution as control(P0.01).The inhibitory effect of BTX-A persisted more than 1 hour.The administration of atropine(1 μmol/L) might completely suppress the frequency,tension and amplitude of spontaneous contractility of duodenal smooth muscle compared to control(P0.01),but the inhibitory effect of atropine persisted only 5 minutes,and then the duodenal spontaneous contractility gradually recovered as compared with that of control with significance(P0.05).The administration of ACh(100 μmol/L) enhanced the frequency,tension and amplitude of spontaneous contractility of duodenal smooth muscle compared to control(P0.01).Subsequently,the respective addition of BTX-A(10 U/ml) or atropine(1 μmol/L) inhibited the contractile response to ACh(P0.01).The administration of ACh(100 μmol/L) did not induce the duodenal smooth muscle contractility after the inhibition with BTX-A(10 U/ml).Conclusion The inhibitory effect of BTX-A on spontaneous contractility of duodenal smooth muscle in vitro suggests the inhibitory efficient time of BTX-A was longer than that of atropine.BTX-A also reduced duodenal muscle contractile response to external addition of ACh.After BTX-A treatment,ACh did no longer agitate duodenal muscle contractile response.These data demonstrate that BTX-A inhibits duodenal smooth muscle contractility suggesting not only inhibition of ACh release from cholinergic nerves but also inhibition of cholinergic muscarinic muscular transmission.