Evidence that superoxide is a mediator of increased blood flow and plasma extravasation in skin

Starr, A. & Brain, S.D. Cardiovascular Division, King’s College London, UK

Reactive oxygen species (ROS) have been shown to mediate potent vasoactive effects in the microcirculation, but many of these are attributed to oxidants that are produced downstream of superoxide (O2- ). O2- is best known as a mediator of decreased blood flow, due to its ability to interact with nitric oxide, and thus inhibit its vasodilator activity (Gryglewski et al., 1986). The aim of this study was to investigate the acute vasoactive effects of O 2 - applied directly to non-inflamed skin.

C57BL/6 mice (female, 25-28 g) were anaesthetised with urethane (2.5 mg/kg i.p.). One group was treated with vehicle (saline i.v.) and the other received a superoxide dismutase (SOD) mimetic (tempol, 30 mg/kg i.v.; Mitchell et al., 1991). Potassium superoxide (KO2) was used as a source of superoxide (as Wang et al., 2004). KO 2 dissolved in Tyrode solution (200 and 400nmol), Tyrode alone (50 μl) or substance P (300pmol) were injected i.d. into either the ear or dorsal skin. Blood flow was measured in the ear by a laser Doppler flow meter and plasma extravasation in ear and dorsal skin by the extravascular accumulation of I125-albumin (as Grant et al., 2004).

Table 1. Effect of KO2 on blood flow and plasma extravasation over 20 minutes in mouse skin. Results expressed as area under recorded flux vs. time curve or μl of plasma per g tissue, mean ± s.e.m. * P<0.05 compared with relevant Tyrode vehicle and P<0.05 compared with tempol vehicle (ANOVA + Bonferroni).

KO2 acted in an acute manner to mediate increased plasma extravasation and blood flow. The SOD mimetic tempol, that removes O2-, inhibited responses to KO2 as expected and in a selective manner as it had no effect on substance P-induced responses. These results provide evidence that O2- can act directly to influence microvascular permeability and increase blood flow, when injected into naïve skin. The mechanisms involved in these responses are under investigation.

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Mitchell JB et al., (1991). Arch Biochem Biophys., 289, 62-70.
Wang ZQ et al., (2004). J Pharmacol Exp Ther., 309, 869-78.

AS is supported by BBSRC.