Inhibition of Nitric Oxide Synthase Attenuates Cutaneous Vasodilation During Warm Moxibustion-Like Thermal Stimulation in Humans

Abstract

This study investigated if nitric oxide (NO) and/or prostaglandin (PG) are responsible for cutaneous vasodilation during warm moxibustion-like thermal stimulation (WMTS). For two protocols, two microdialysis membranes were placed in the medial forearm skin. In the first protocol (n=8), the sites were randomly assigned and perfused with N(G)-nitro-l-arginine methyl ester hydrochloride (l-NAME), an NO synthase inhibitor or Ringer's solution (control site). Similarly, two microdialysis membranes were placed in the medial forearm skin in the second protocol (n=6). One site was perfused with ketorolac (Keto), the cyclo-oxygenase (COX) pathway inhibitor, and the other site was perfused with Ringer's solution (control site). In both protocols, cutaneous vasodilation was induced using WMTS with an electronic warm moxibustion treatment appliance. After 10 minutes of baseline recording, WMTS was applied to the forearm skin for 20 minutes and recovery was monitored over a period of 20 minutes. Skin blood flow (SkBF) at each site was measured using laser-Doppler flowmetry. Cutaneous vascular conductance (CVC) was calculated as laser-Doppler flux/mean arterial blood pressure (BP). The study was conducted in a laboratory at the Kansai University of Health Sciences. The subjects were 14 healthy male volunteers. WMTS was applied to the medial forearm skin using an electronic warm moxibustion treatment appliance. SkBF, skin temperature (Tsk), core body temperature (Tc), heart rate (HR), and BP were outcome measures. In the first protocol, peak CVC values during WMTS at the site perfused with l-NAME were significantly decreased, compared to those at the control site (p<0.05). In the second protocol, peak CVC values during WMTS did not differ between the control site and the Keto site (p>0.05). These data demonstrate that NO is involved in the mechanism of cutaneous vasodilation induced by WMTS. Furthermore, increases in CVC despite inhibition of the COX pathway suggest that PG does not contribute to cutaneous vasodilation during WMTS.