The Effect of Methylphenidate on Cutaneous Blood Flow During Passive Hyperthermia: The Role of Nitric Oxide

Abstract

Whole body heat stress causes a reflex cutaneous vasodilator response driven by a sympathetic active vasodilatory system. Methylphenidate (MPD) is known to increase whole body sympathetic activity, potentially leading to increased cutaneous blood flow via a nitric oxide (NO) based pathway. We investigated forearm SkBF during whole-body heat stress (Tc Δ + 1.5˚C) with and without MPD (20 mg) ingestion in 6 adult males (23 ± 2 y) using laser-Doppler flowmetry and L-NAME to inhibit NOS (Nitric Oxide Synthase). Increasing Tc led to higher forearm cutaneous vascular conductance (CVC) (p < 0.05) and area under the curve of CVC (AUC) (p < 0.001) measures. L-NAME had a significant effect on CVC (p < 0.05), but not AUC (p = 0.696). MPD had no significant effect on CVC (p = 0.836) or AUC values (p = 0.261). With an increase in Tc, there was a significantly greater contribution of NO to the increase in SkBF, as expected (p < 0.05). Conversely, MPD had no effect on NO contribution to forearm SkBF (p = 0.970). Though not significant, a trend in which MPD decreased time to reflex SkBF plateau was observed (p = 0.200). These data suggest that NO has a role to play in reflex vasodilation, but MPD does not significantly increase SkBF.