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 remains 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 (n=17, protocol 1) and the administration of adrenergic agonists epinephrine and norepinephrine (n=16, protocol 2) 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 protocol 1. In protocol 1, relative to the separate administration of propranolol, terazosin alone or in combination with propranolol attenuated exercise sweating to a similar extent (both P£0.037), although the effect was reduced relative to that observed with bretylium treatment (P<0.001). In protocol 2, administration of propranolol increased norepinephrine- (P=0.029) but not epinephrine-induced sweat rate. The combined administration of terazosin reversed this response, attenuating sweating (P<0.001) to a greater extent than terazosin treatment alone (P=0.030). Altogether, we showed that while β-adrenergic receptors may interact with α-adrenergic receptors pharmacologically, it does not appear to modulate exercise-induced sweating on the forearm. Further, 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.