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document
Intravenous adenosine activates diffuse nociceptive inhibitory controls in humans . Experimentally induced pain can be attenuated by concomitant heterotopic nociceptive stimuli ( counterirritation ) . Animal data indicate that this stems from supraspinal " diffuse noxious inhibitory controls " ( DNICs ) triggered by C and Aδ fibers . In humans , only noxious stimuli induce counterirritation . This points at C fibers , but the effects of pharmacologically stimulating C fibers have not been studied . Intravenous adenosine activates pulmonary C fibers and induces dyspnea . This study tests the hypothesis that putative activation of pulmonary C fibers by adenosine would trigger DNICs in humans and induce counterirritation . Twelve healthy volunteers were included ( with valid results available in 9 ) and studied according to a double-blind , randomized , cross-over design ( intravenous adenosine , 140 μg·kg ( -1 ) ·min ( -1 ) , during 5 min vs. placebo ) . We measured ventilatory variables and end-tidal CO2 tension , dyspnea intensity by visual analog scale , and the intensity of putative chest pain . The primary outcome was the amplitude of the RIII component of the nociceptive flexor reflex recorded by biceps femoris electromyogram in response to painful electrical sural nerve stimulation ( RIII ) , taken as a substitute for pain perception . Placebo did not induce any significant effect . Adenosine induced dyspnea , hyperpnea , tachycardia , and significant RIII inhibition ( 24 ± 8 % at the 4th min , P < 0.0001 ) . The temporal dynamics of adenosine-induced dyspnea and RIII inhibition differed ( immediate onset followed by a slow decrease for dyspnea , slower onset for RIII inhibition ) . Intravenous adenosine in normal humans induces counterirritation , fueling the notion that C-fiber stimulation trigger DNICs in humans . The temporal dissociation between adenosine-induced dyspnea and RIII inhibition suggests that C fibers other than pulmonary ones might be involved .
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Intervention_Pharmacological
adenosine
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Intervention_Pharmacological
intravenous adenosine
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Intervention_Control
placebo
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Intervention_Control
Placebo
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Intervention_Pharmacological
Adenosine
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Outcome_Physical
supraspinal " diffuse noxious inhibitory controls " ( DNICs )