Does alpha1-adrenergic receptor blockade modulate sweating during incremental exercise in young endurance-trained men?

PURPOSE: Human eccrine sweat glands respond to alpha1-adrenergic receptor agonists. We recently reported that adrenergic mechanisms contribute to sweating in endurance-trained men during an incremental exercise to volitional fatigue. However, it remains unclear if this response is mediated by alpha1-adrenergic receptor activation. METHODS: Twelve endurance-trained men performed an incremental cycling bout until exhaustion while wearing a water-perfused suit to clamp skin temperature at ~ 34 degrees C. Bilateral forearm sweat rates were measured wherein the distal area was treated with either 1% terazosin (alpha1-adrenergic receptor antagonist) or saline solution on the opposite limb (Control) via transdermal iontophoresis. We also measured proximal bilateral forearm sweat rate in untreated sites to confirm that no between-limb differences in forearm sweat rate occurred. Once sweat rate returned to pre-exercise resting levels at ~ 20 min postexercise, 0.25% phenylephrine (alpha1-adrenergic receptor agonist) was iontophoretically administered to skin to verify alpha1-adrenergic receptor blockade. RESULTS: Sweat rates at the proximal untreated right and left forearm sites were similar during exercise (interaction, P = 0.581). Similarly, no effect of terazosin on sweat rate was measured relative to control site (interaction, P = 0.848). Postexercise administration of phenylephrine increased sweat rate at the control site (0.08 +/- 0.09 mg cm(-2) min(-1)), which was suppressed by ~ 90% at the terazosin-treated site (0.01 +/- 0.02 mg cm(-2) min(-1)) (P = 0.026), confirming that alpha1-adrenergic receptor blockade was intact. CONCLUSION: Our findings demonstrate that alpha1-adrenergic receptors located at eccrine sweat glands do not contribute to eccrine sweating during incremental exercise in young endurance-trained men.