Adenosine receptor blockade accentuates the responses of muscle sympathetic nerve activity to fatiguing exercise

Abstract

The role adenosine plays in evoking the exercise pressor reflex in humans remain controversial. Interestingly, animal studies suggest that adenosine can inhibit type 1 vanilloid receptors activity. Thus, we hypothesized that adenosine receptor blockade would accentuate muscle sympathetic nerves activity (MSNA) response to fatiguing exercise in humans. Blood pressure (Finometer), heart rate, and MSNA from peroneal nerve were assessed in 11 healthy young volunteers during fatiguing isometric handgrip, post exercise muscle ischemia (PEMI), and passive muscle stretch during PEMI. The protocol was performed before and after adenosine receptor blockade by local infusion of 40 mg aminophylline in saline via forearm Bier block (regional intravenous anesthesia). In the second experiment, the same amount of saline was infused via the Bier block. After aminophylline, the MSNA and blood pressure responses to fatiguing handgrip, PEMI and passive stretch (all P<0.05) were significantly greater than those in control condition. Saline Bier block had no similar effects on the MSNA and blood pressure responses. These data verified our hypothesis, and suggest that adenosine may act to inhibit MSNA response in exercise pressor reflex. Supported by NIH P01 HL077670, M01 RR010732 and AHA 0635245 N.