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

Abstract

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 α1- and α2-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 ≈15% and attenuated (P<0.05) the leg vasoconstrictor response to arterial infusion of tyramine (α1- and α2-adrenergic receptor stimulation) by ≈15%, whereas the response to the α1-agonist phenylephrine was unchanged. Inhibition of α1-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 α1-adrenoceptors and in the constrictive effect of noradrenaline via α2-adrenoceptors, thereby contributing to the regulation of peripheral vascular resistance and blood pressure in humans.

Response by Good et al to Letter Regarding Article, “Pannexin-1 Channels as an Unexpected New Target of the Antihypertensive Drug Spironolactone”

“…Wright and Angus for the opportunity to clarify these points. In this response, we reiterate substantial evidence from other groups in mouse and human 8, 13 , including their own work 6 , to support the basic mechanism for Panx1 contributions to α1AR-mediated vasoconstriction. We also note that our work provides strong evidence that spironolactone is a Panx1 channel inhibitor, adding an important new arrow to the pharmacological quiver.…”

Interaction Between Pannexin 1 and Caveolin-1 in Smooth Muscle Can Regulate Blood Pressure

“…Recently, our group and others 21–24 have elucidated in mouse and humans an α–AR signaling axis that activates Pannexin 1 channels. Pannexins are a family of transmembrane channel-forming glycoproteins that have emerged as the physiological conduit for controlled ATP release from vascular and non-vascular cell types 25–27 .…”

Exercise training reverses an age‐related attenuation in ATP signaling in human skeletal muscle

“…This limb difference most likely reflects our upright posture as unlike quadrupeds, the legs of humans are subjected to a substantially higher hydrostatic pressure relative to the arms. Accordingly, the legs display greater arterial wall thickness, enhanced adrenergic responsiveness, and a reduced vasodilator response to ACh and sodium nitroprusside . Hence, the observed difference in the role of aging on ATP signaling between the forearm and leg adds an additional piece to the puzzle with regard to understanding the marked dissimilarity in vascular regulation of the upper and lower extremities.…”