Transient hyperaemic response to assess vascular reactivity of skin: effect of locally iontophoresed acetylcholine, bradykinin, epinephrine and phenylephrine.

BACKGROUND Recently, the transient hyperaemic response (THR) to brief compression (20 s) of the brachial artery has been described as a way to assess vascular reactivity of the forearm skin. We studied the effects of locally iontophoresed vasoactive agents on this response in 20 male volunteers. METHODS An iontophoresis chamber attached to the anterior forearm permitted simultaneous administration of drugs by iontophoresis and measurement of skin blood flow-flux by laser Doppler probe. Three THR tests were performed before and after iontophoresis by compressing the brachial artery with digital pressure for 20 s and then releasing. The following were iontophoresed: saline 0.9% (iontophoresis vehicle control), acetylcholine, bradykinin, epinephrine and phenylephrine. The THR ratio (THRR) was calculated as F2/F1 where F1 was baseline blood flow-flux immediately before compression and F2 was peak blood flow-flux after release. RESULTS When compared with saline 0.9%, acetylcholine and bradykinin increased median F1 from 9.2 (range 5.2-23.8) to 22.1 (8.7-61.5) and from 4.8 (3.0-23.2) to 15.0 (2.5-31.8), respectively, and reduced THRR from 1.26 (1.07-2.2) to 0.99 (0.93-1.04) and from 1.63 (1.06-2.58) to 1.09 (0.93-1.19), respectively. Epinephrine, but not phenylephrine, caused a significant reduction in F1 from 9.2 (5.2-23.8) to 4.0 (1.5-22.3). Neither epinephrine nor phenylephrine had significant effect on THRR. CONCLUSIONS Iontophoresed acetylcholine and bradykinin significantly increase the flow-flux and impair THR in forearm skin, further validating the concept that THR represents true vasodilatation during arterial occlusion. In addition, iontophoresis of vasoconstrictors does not appear to have any consistent effect.