Role of Nitric Oxide in the Visible Light-Induced Rapid Increase of Human Skin Microcirculation at the Local and Systemic Levels: II. Healthy Volunteers

Abstract

The aim of this study is to evaluate the skin microcirculation increase seen in healthy volunteers after a single exposure to polychromatic visible (pVIS) light, and to prove the role of nitric oxide (NO) in the development of this effect. Improvement of microcirculation is one of the most important effects of laser and pVIS light therapy; however, its mechanism of action remains unknown. A main role in the regulation of vascular tone is known to be played by NO. It is produced by NO-synthase (NOS) located in membranes of many cells, including endothelial and blood cells. NOS, a biopteroflavohemoprotein, absorbs pVIS light, resulting in its activation. The central area of the dorsal side of the right hand (24 cm2) of 42 volunteers was irradiated for 5 min with pVIS light from a Q-light (385-750 nm, 95% polarization, 40 mW/cm2, 12 J/cm2). Then for 90 min, the blood flow rate (Qas) was measured eight times, both in the area of the irradiation (local effect) and in the non-irradiated left hand (systemic effect) by using a high-frequency ultrasound Doppler device, recording Qas in human skin to a depth up to 5 mm. In the central area of the right hand of 14 volunteers an NOS inhibitor, N-monomethyl-L-arginine (L-NMMA, 0.1% solution), was iontophoretically administered prior to exposure, whereas in 10 other subjects it was administered to the left hand with subsequent exposure of the right hand. As soon as 2 min after exposure, Qas in the irradiated area rose on average by 32%, and in 20 min by 45%; it then decreased and in 90 min returned to the initial level. A statistically significant Qas increase in the non-irradiated hand was recorded in 5 min (+9%), and in 20 min it reached a maximum level (+39%), and 90 min later it decreased to the initial values. The presence of L-NMMA in the light-exposed area completely blocked the photoinduced rise of microcirculation, both in the irradiated and in non-irradiated hand; however, its administration to the non-irradiated hand did not prevent these effects. The increase in skin microcirculation produced by pVIS light at the local and systemic levels is due to activation of NO synthesis in the irradiated area.