Effect of captopril on skin blood flow following intradermal bradykinin measured by laser Doppler flowmetry

The effect of captopril on skin response to intradermal injection of bradykinin was investigated by laser Doppler flowmetry (LDF) and weal and flare measurements in this randomised, double-blind, placebo-controlled, cross-over balanced study. Intradermal injections of 1 and 2.5 micrograms of bradykinin and normal saline were made into the forearm skin of six healthy volunteers between 1 and 2 h (t1) and between 3 and 4 h (t2) after either 25 mg captopril or placebo. Skin blood flow outside the induced weal was monitored continuously by LDF for 15 min and the mean LDF values over the last 15 s were used for analysis. Weal and flare sizes were measured at 15 min. On the placebo days, the mean LDF output, weal volume and flare area increased with incremental bradykinin dose. Pre-treatment with captopril significantly increased LDF output following intradermal bradykinin at t1 but not at t2. At both t1 and t2, captopril significantly increased weal volume. There was no significant difference between treatments in flare areas. Skin response following intradermal normal saline, measured by the above parameters, was not affected by captopril. This study showed that captopril potentiated the effects of intradermal bradykinin both with respect to blood flow changes and weal formation. The non-invasive technique of LDF can be used to detect the skin blood flow changes induced by intradermal bradykinin and the potentiation of this effect by captopril. It appears to be a useful and more objective method of quantifying local cutaneous blood flow changes than measurement of flare area.