Submitted on July 22, 2002
Accepted on March 18, 2003
Inhibitory Effects of Botulinum Toxin on Pyloric and Antral Smooth Muscle
Arlene N. James1, James P. Ryan2, and Henry P. Parkman3*
1 Department of Medicine, Temple University School of Medicine, Philadelphia, PA, USA
2 Department of Physiology, Temple University School of Medicine, Philadelphia, PA, USA
3 Department of Medicine, Temple University School of Medicine, Philadelphia, PA, USA; Department of Physiology, Temple University School of Medicine, Philadelphia, PA, USA
* To whom correspondence should be addressed. E-mail: henry.parkman{at}.temple.edu.
Botulinum toxin injection into the pylorus is reported to improve gastric emptying in gastroparesis. Classically, botulinum toxin inhibits acetylcholine (ACh) release from cholinergic nerves in skeletal muscle. Aim: To determine the effects of botulinum toxin on pyloric smooth muscle. Methods: Guinea pig pyloric muscle strips were studied in vitro. Botulinum toxin type A was added; electric field stimulation (EFS) was performed every 30 mins for 6 hrs. ACh 100 µM-induced contractile responses were determined prior to and after 6 hrs. Results: Botulinum toxin caused a concentration dependent decrease of pyloric contractions to EFS. At a low concentration (2 units/ml), botulinum toxin decreased pyloric contractions to EFS by 43±9% without affecting ACh-induced contractions. At higher concentrations (10 units/ml), botulinum toxin decreased pyloric contraction to EFS by 75±7% and decreased ACh-induced contraction by 79±9%. Conclusions: Botulinum toxin inhibits pyloric smooth muscle contractility. At a low concentration, botulinum toxin decreases EFS-induced contractile responses without affecting ACh-induced contractions suggesting inhibition of ACh release from cholinergic nerves. At higher concentrations, botulinum toxin directly inhibits smooth muscle contractility as evidenced by the decreased contractile response to ACh.
