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

Abstract

Adequate blood supply is the most important factor for the survival of a random pattern skin flap, and injuries to the vascularity of the flap may result in flap necrosis. Botulinum toxin-A (BoTA) has become a widely used pharmacologic agent for aesthetic purposes as well as for its vasomotor actions. The mechanism of action of this agent suggests that it may be useful in controlling vasospastic conditions and for the management of ischemic tissues. This study was conducted to establish whether local application of BoTA increases skin flap survival by inhibiting vasoconstriction, which is influenced by changes in vasoconstrictor neurotransmitters. Using a caudally-based random pattern skin flap model, 40 adult Sprague-Dawley rats were divided into two groups and pretreated with BoTA or saline. Skin flaps were elevated and reinset, and the survival areas were evaluated on postoperative days 3 and 7. To serially assess changes of cutaneous blood flow in the flap, four serial measurements were taken from each flap using a laser Doppler flowmeter. The changes in features and number of vessels were documented using histological and immunohistochemical analysis after injection of BoTA. Vasoconstrictor neurotransmitters were quantitatively analyzed by high performance liquid chromatography, western blots, and colorimetric assay, and included norepinephrine (NE), neuropeptide Y (NPY), nitric oxide (NO), and endothelial nitric oxide synthase (eNOS). The mean survival rate of BoTA treated flaps was significantly higher than that of the control group on postoperative days 3 and 7. The blood flow in the BoTA group was significantly increased in the proximal and middle areas immediately after the operation and in all of the areas on postoperative day 3. The average number of CD31-positive vessels in the BoTA group was significantly higher than in the control group. NE levels in the BoTA group were significantly decreased compared with those in the control group immediately after flap elevation and at 3 days postoperatively. Although NPY levels appeared elevated at each of the observed periods, there were no significant differences between the two groups. NO levels were unchanged in both groups despite significant increases of eNOS protein levels immediately after flap elevation and at postoperative day 3.In conclusion, BoTA increases the vascular blood flow and survival of random pattern skin flaps in rats through reduced levels of NE. In contrast, NPY, another vasoconstrictor, is not affected by BoTA treatment. Likewise, the level of NO, a vasodilating cotransmitter, is not affected by BoTA despite significant increases of eNOS protein levels in the flaps