Iontophoretic transdermal administration of NG-nitro-l-arginine methyl ester hydrochloride [l-NAME, a nitric oxide synthase (NOS) inhibitor] has been used as a non-invasive evaluation of NOS-dependent mechanisms in human skin. However, the availability has yet to be investigated in sweating research. Prior observations using invasive techniques (e.g., intradermal microdialysis technique) to administer l-NAME have implicated that NOS reduces sweating induced by heat stress but rarely influences the response induced by the administration of cholinergic muscarinic receptor agonists. Therefore, we investigated whether the transdermal iontophoretic administration of l-NAME modulates sweating similar to those prior observations. Twenty young healthy adults (10 males, 10 females) participated in two experimental protocols on separate days. Before each protocol, saline (control) and 1% l-NAME were bilaterally administered to the forearm skin via transdermal iontophoresis. In protocol 1, 0.001% and 1% pilocarpine were iontophoretically administered at l-NAME-treated and untreated sites. In protocol 2, passive heating was applied by immersing the lower limbs in hot water (43 °C) until the rectal temperature increased by 0.8 °C above baseline. The sweat rate was continuously measured throughout both protocols. Pilocarpine-induced sweat rate was not significantly different between the control and l-NAME-treated sites in both pilocarpine concentrations (P ≥ 0.316 for the treatment effect and interaction of treatment and pilocarpine concentration). The sweat rate during passive heating was attenuated at the l-NAME-treated site relative to the control (treatment effect, P = 0.020). Notably, these observations are consistent with prior sweating studies administrating l-NAME into human skin using intradermal microdialysis techniques. Based on the similarity of our results with already known observations, we conclude that transdermal iontophoresis of l-NAME is a valid non-invasive technique for the investigation of the mechanisms of sweating related to NOS during heat stress.
Keywords: Eccrine sweat gland; Heat loss response; Iontophoresis; Muscarinic receptor; Sex difference; Thermoregulation.
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