Human cutaneous reactive hyperaemia:: role of BKCa channels and sensory nerves

Reactive hyperaemia is the increase in blood flow following arterial occlusion. The exact mechanisms mediating this response in skin are not fully understood. The purpose of this study was to investigate the individual and combined contributions of (1) sensory nerves and large-conductance calcium activated potassium (BKCa) channels, and (2) nitric oxide (NO) and prostanoids to cutaneous reactive hyperaemia. Laser-Doppler flowmetry was used to measure skin blood flow in a total of 18 subjects. Peak blood flow(BF) was defined as the highest blood flow value after release of the pressure cuff. Total hyperaemic response was calculated by taking the area under the curve (AUC) of the hyperaemic response minus baseline. Infusates were perfused through forearm skin using microdialysis in four sites. In the sensory nerve/BKCa protocol: (1) EMLA (R) cream ( EMLA, applied topically to skin surface), (2) tetraethylammonium (TEA), (3) EMLA (R) + TEA (Combo), and (4) Ringer solution (Control). In the prostanoid/NO protocol: (1) ketorolac ( Keto), (2) N-G-nitro-L-arginine methyl ester (L-NAME), (3) Keto + L-NAME (Combo), and (4) Ringer solution (Control). CVC was calculated as flux/mean arterial pressure and normalized to maximal flow. Hyperaemic responses in Control ( 1389 +/- 794% CVCmax s) were significantly greater compared to TEA, EMLA and Combo sites ( TEA, 630 +/- 512, P = 0.003; EMLA, 421 +/- 216, P < 0.001; Combo, 201 +/- 200, P < 0.001% CVCmax s). Furthermore, AUC in Combo ( Keto + L-NAME) site was significantly greater than Control (4109 +/- 2777 versus 1295 +/- 368% CVCmax s). These data suggest (1) sensory nerves and BKCa channels play major roles in the EDHF component of reactive hyperaemia and appear to work partly independent of each other, and (2) the COX pathway does not appear to have a vasodilatory role in cutaneous reactive hyperaemia.