Interstitial adenosine is increased during intermittent isometric exercise (handgrip) and may be an afferent signal for the pressor reflex. The effect of the nucleoside transport inhibitor dipyridamole on interstitial adenosine concentration has never been studied in humans.
The aim of the study was to determine whether dipyridamole increases interstitial adenosine during handgrip and potentiates the exercise-induced pressor reflex.
In nine healthy volunteers, isometric hand-contractions (50% of maximal force) were performed with and without dipyridamole (12 mg 100 ml−1 min−1, infused into the brachial artery). Interstitial adenosine was measured in the flexor digitorum superficialis muscle using microdialysis with h.p.l.c. detection. Blood pressure was measured at 2 min intervals (Dinamap). Peroneal nerve muscle sympathetic nerve activity (MSNA) was successfully recorded in four volunteers.
Intermittent handgrip increased dialysate adenosine by 0.3 ± 0.1 and 0.5 ± 0.1 nmol ml−1 in the absence and presence of dipyridamole respectively (mean ± s.e. mean; P < 0.05 for effect of dipyridamole). Dipyridamole did not augment the handgrip-induced rise in MSNA in any of the volunteers. Handgrip increased blood pressure (SBP/DBP) by 9.6 ± 2.4/4.5 ± 2.0 and 10.4 ± 2.2/7.0 ± 1.3 mmHg in the absence and presence of dipyridamole respectively (P = NS for dipyridamole effect). In none of the volunteers, dipyridamole augmented the exercise-induced rise in MSNA.
Dipyridamole increases interstitial adenosine during handgrip but does not potentiate the pressor reflex. Our data do not support a role for adenosine as a trigger of the exercise-induced pressor reflex in healthy volunteers.