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Microcirculatory effects of Botulinum Toxin A in the Rat: Acute and Chronic Vasodilation
Somjade J. Songcharoen, MD, Roberto G. Aru, BS, Samantha R. Seals, PhD, Peter B. Arnold, MD, PhD, Robert L. Hester, PhD.
University of Mississippi Medical Center, Jackson, MS, USA.

PURPOSE:
This study aims to examine the microcirculatory changes and response to functionally different topical vasodilators after pretreatment with Botulinum toxin A (BTX).
METHODS:
The spinotrapezius muscle of Sprague-Dawley rats underwent a single 2-week pretreatment with either 0.2ml saline (n=3) or 2u Botulinum Toxin A (n=3), followed by surgical elevation. An arcade arteriole was chosen for microcirculatory observation. Using a video caliper device, the inner diameter was measured at 30s intervals following sequential superfusion of nitroglycerin at 100mcg/ml and 200mcg/ml, as well as multiple concentrations lidocaine followed by pharmacologically induced maximum dilation.
RESULTS:
On average, time to dilation was 3.2 min and return to baseline was 5.2 min. Baseline and dilation diameters are expressed as a percent of maximum induced dilation. The mean baseline was 59% and mean dilation was 74% with no significant difference between any of the drug groups. However, the mean baseline diameter after BTX pretreatment was 21% higher than saline pretreatment (p=0.0004). Furthermore, mean dilation was 11% greater in the BTX pretreatment group, although non-significant (p=0.08). BTX pretreatment had a greater impact on dilation than different topical treatments alone.
CONCLUSION:
Pretreatment with BTX induces the resting diameter of arterioles to be closer to their maximum potential. Its chronic addition increases the acute effect of topical vasodilators. We present a novel method for real-time observation of acute and chronic microvascular effects of BTX. Further studies are taking place with larger sample sizes in conjunction with methods to correlate changes in blood flow and vessel density.


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