Do ATP and hydrogen peroxide cause sympatholysis in rat soleus feed arteries?

Arteries and arterioles constrict less to sympathetic stimulation in contracting compared to resting skeletal muscle (sympatholysis). There is some uncertainty regarding the specific agents causing sympatholysis. We have shown that acidosis, but not shear stress, potassium, or adenosine, is sympatholytic in feed arteries from the predominantly slow twitch soleus muscle. Interstitial fluid concentrations of both adenosine triphosphate (ATP) and hydrogen peroxide (H2O2) increase in contracting skeletal muscle, and we hypothesized that ATP and H2O2 are sympatholytic. Soleus feed arteries (n = 6 per group) were isolated from male Sprague-Dawley rats and cannulated on two glass micropipettes for in vitro videomicroscopy. We measured the constriction response to the α-1 adrenergic receptor agonist phenylephrine (PE; 10-9 M to 10-4 M, 0.5 log increments) in the presence of varying physiological levels of ATP (0 uM, 1 uM, 10 uM, and 100 uM) and H2O2 (0 uM, 1 uM, 10 uM, and 100 uM). Our data indicate no significant difference in PE-induced constriction between levels of ATP (maximum constriction 64.1 10.4 % vs. 74.4 8.1 %, 68.9 8.7 %, and 66.1 11.4 %) or H2O2 (maximum constriction 76.9 9.2 % vs. 77.5 5.7 %, 79.7 1.8 %, and 76.5 8.0 %). We conclude that neither ATP nor H2O2 independently cause sympatholysis of α-1 adrenergic receptors in rat soleus feed arteries