Probenecid Inhibits -Adrenergic Receptor-Mediated Vasoconstriction in the Human Leg Vasculature

Coordination of vascular smooth muscle cell tone in resistance arteries plays an essential role in the regulation of peripheral resistance and overall blood pressure. Recent observations in animals have provided evidence for a coupling between adrenoceptors and Panx1 (pannexin-1) channels in the regulation of sympathetic nervous control of peripheral vascular resistance and blood pressure; however, evidence for a functional coupling in humans is lacking. We determined Panx1 expression and effects of treatment with the pharmacological Panx1 channel inhibitor probenecid on the vasoconstrictor response to 1- and 2-adrenergic receptor stimulation in the human forearm and leg vasculature of young healthy male subjects (23 +/- 3 years). By use of immunolabeling and confocal microscopy, Panx1 channels were found to be expressed in vascular smooth muscle cells of arterioles in human leg skeletal muscle. Probenecid treatment increased (P<0.05) leg vascular conductance at baseline by approximate to 15% and attenuated (P<0.05) the leg vasoconstrictor response to arterial infusion of tyramine (1- and 2-adrenergic receptor stimulation) by approximate to 15%, whereas the response to the 1-agonist phenylephrine was unchanged. Inhibition of 1-adrenoceptors prevented the probenecid-induced increase in baseline leg vascular conductance, but did not alter the effect of probenecid on the vascular response to tyramine. No differences with probenecid treatment were detected in the forearm. These observations provide the first line of evidence in humans for a functional role of Panx1 channels in setting resting tone via 1-adrenoceptors and in the constrictive effect of noradrenaline via 2-adrenoceptors, thereby contributing to the regulation of peripheral vascular resistance and blood pressure in humans.