Effect of botulinum toxin A on vasoconstriction and sympathetic neurotransmitters in a murine random pattern skin flap model.

Blood supply is the most important factor determining the survival of a skin flap. Botulinum toxin-A (Botox-A) is used as pharmacologic agent not only for aesthetic purposes, but also for its vasomotor actions. This study was conducted to establish whether local application of Botox-A increased survival of random pattern skin flaps in rats by changing the expression of neurotransmitters. Forty adult Sprague-Dawley rats with a caudally-based random pattern skin flap were divided into two groups: Botox-A group and saline group. Surviving flap area and cutaneous blood flow in the flap were evaluated on postoperative days 3 and 7. After injection of Botox-A, changes in vessels were analyzed using immunohistochemical staining. Levels of norepinephrine, neuropeptide-Y, nitric oxide, and endothelial nitric oxide synthase were analyzed quantitatively by high performance liquid chromatography, Western blot, and colorimetric assay. The survived area in the Botox-A group was significantly higher than that in the control group on postoperative days 3 and 7. Blood flow in the Botox-A group was significantly high in the proximal and middle areas immediately after the operation. The number of CD31-positive vessels in the Botox-A group was significant greater than that in the control group. Norepinephrine level in the Botox-A group decreased significantly immediately after flap elevation and at postoperative day 3. There were no significant differences in neuropeptide-Y level between the two groups. Nitric oxide level did not change significantly in either group despite the increase in endothelial nitric oxide synthase immediately after flap elevation and at 3 days postoperatively. In conclusion, Botox-A increased vascular blood flow and viable flap area in rats by reducing norepinephrine level. In contrast, neuropeptide-Y, another vasoconstrictor, was not affected by Botox-A. Nitric oxide, a vasodilator, was also not affected by Botox-A, despite the significant increase in endothelial nitric oxide synthase expression in the flaps.