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ATP Antagonism Attenuates the Reflex Cutaneous Vasoconstriction Response in Humans

Norepinephrine is responsible for ~60% of the reflex cutaneous VC response in young individuals, whereas the remainder is due to a coreleased sympathetic adrenergic neurotransmitter(s) that has yet to be identified. There is conflicting evidence supporting neuropeptide Y in this role; however, other putative cotransmitters have yet to be tested in human skin. We hypothesize that ATP contributes to the reflex cutaneous VC response to whole‐body cooling (Tsk = 30.5 oC). Three microdialysis (MD) fibers were placed in the forearm skin of 7 (25 ± 1 years; 4 males, 3 females) individuals for infusion of 1) lactated Ringer's solution (control), 2) 10 mM L‐NAME, and 3) purinergic receptor blockade with 1mM suramin + L‐NAME. Laser Doppler flux (LDF) was measured over each MD site and cutaneous vascular conductance (CVC) was calculated as CVC = LDF/mean arterial pressure and expressed as a percent change from baseline (%ΔCVC). L‐NAME was used to block the vasodilatory influence of ATP and unmask the P2X‐mediated VC response to exogenous ATP infusion (‐18 ± 2 %ΔCVC). This response was blocked in the suramin‐pretreated site (‐2 ± 1 %ΔCVC). During whole body cooling (Tsk = 30.5 oC), the VC response in the suramin site was attenuated (‐24 ± 3 %ΔCVC; p < 0.05) compared to the control site (‐35 ± 4 %ΔCVC). These data suggest that ATP has a contributory role in the reflex cutaneous VC response in humans during whole‐body cooling.