Separate and combined blockades of α- and β-adrenergic receptors in forearm sweating induced by adrenergic agents and exercise in the heat in young adults

The assessment of adrenergic modulation of sweating as assessed via pharmacologic administration of α- and β-adrenergic receptor blockers during exercise has yielded mixed findings. However, the underlying mechanisms for this disparity remain unresolved. We investigated the effects of separate and combined blockade of α- and β-adrenergic receptors on forearm sweating induced by a 30-min moderate-intensity exercise bout (<i>n</i> = 17, <i>protocol 1</i>) and the administration of adrenergic agonists epinephrine and norepinephrine (<i>n</i> = 16, <i>protocol 2</i>) in the heat. Adrenergic receptor blockade was induced via the separate and combined iontophoretic administration of terazosin (α-adrenergic receptor antagonist) and propranolol (β-adrenergic receptor antagonist) on forearm skin. Bretylium, a noradrenergic sympathetic nerve inhibitor, was also administered separately in <i>protocol 1</i>. In <i>protocol 1</i>, relative to the separate administration of propranolol, terazosin alone or in combination with propranolol attenuated exercise sweating to a similar extent (both <i>P</i> ≤ 0.037), although the effect was reduced relative to that observed with bretylium treatment (<i>P</i> < 0.001). In <i>protocol 2</i>, administration of propranolol increased norepinephrine- (<i>P</i> = 0.029) but not epinephrine-induced sweat rate. The combined administration of terazosin reversed this response, attenuating sweating (<i>P</i> < 0.001) to a greater extent than terazosin treatment alone (<i>P</i> = 0.030). Altogether, we showed that although β-adrenergic receptors may interact with α-adrenergic receptors pharmacologically, it does not appear to modulate exercise-induced sweating on the forearm. Furthermore, α- but not β-adrenergic receptors independently modulate the regulation of forearm sweating during exercise in the heat. Finally, the bretylium-induced reduction in forearm sweat rate during exercise likely occurs independently of α- and β-adrenergic receptors.<b>NEW & NOTEWORTHY</b> Pharmacological stimulation of α- and β-adrenergic receptors produces sweating in vivo. Still, the separate and interactive roles of these adrenergic receptors during exercise and pharmacological adrenergic stimulation in the heat remain unknown. We showed that β-adrenergic receptors may interact with α-adrenergic receptors pharmacologically, but it does not modulate exercise-induced sweating. The α-adrenergic receptors independently modulate sweating during exercise in the heat. We provide important new insights into our understanding of the mechanisms regulating human sweating.