UVA Irradiation of Human Skin Vasodilates Arterial Vasculature and Lowers Blood Pressure Independently of Nitric Oxide Synthase

Abstract

The incidence of hypertension and cardiovascular disease (CVD) correlates with latitude and rises in winter. The molecular basis for this remains obscure. As nitric oxide (NO) metabolites are abundant in human skin, we hypothesized that exposure to UVA may mobilize NO bioactivity into the circulation to exert beneficial cardiovascular effects independently of vitamin D. In 24 healthy volunteers, irradiation of the skin with two standard erythemal doses of UVA lowered blood pressure (BP), with concomitant decreases in circulating nitrate and rises in nitrite concentrations. Unexpectedly, acute dietary intervention aimed at modulating systemic nitrate availability had no effect on UV-induced hemodynamic changes, indicating that cardiovascular effects were not mediated via direct utilization of circulating nitrate. UVA irradiation of the forearm caused increased blood flow independently of NO synthase (NOS) activity, suggesting involvement of pre-formed cutaneous NO stores. Confocal fluorescence microscopy studies of human skin pre-labeled with the NO-imaging probe diaminofluorescein 2 diacetate revealed that UVA-induced NO release occurs in a NOS-independent, dose-dependent manner, with the majority of the light-sensitive NO pool in the upper epidermis. Collectively, our data provide mechanistic insights into an important function of the skin in modulating systemic NO bioavailability, which may account for the latitudinal and seasonal variations of BP and CVD.

Acute whole body UVA irradiation combined with nitrate ingestion enhances time trial performance in trained cyclists

“…In contrast to our hypothesis and previous research (Mowbray et al, 2009, Oplander et al, 2009, Liu et al, 2014, exposure to UV-A light resulted in only a small, non-significant increase in plasma nitrite concentration compared to baseline. However, plasma nitrite declined from pre-to post-light exposure in the two SHAM trials (by 43 nM in PLA + SHAM and 69 nM in NIT + SHAM), a finding also reported by Liu and colleagues (2014).…”

“…A Waldmann GH-8 ST unit (Herbert Waldmann, GmbH, Villingen-Schwenningen, Germany) containing eight, F851 100W UV-A bulbs (320-410nm; maximum 351 nm), was positioned 20 cm from the body. At this distance a dose of 20 J/cm 2 was produced which is the equivalent to two standard epithelial doses or 30 min exposure to sunlight at noon on a sunny day in Southern Europe (Liu et al, 2014). This dose of UV-A light has been shown to significantly increase plasma nitrite immediately after irradiation with values remaining elevated at least 40 min after exposure (Liu et al, 2014).…”

“…At this distance a dose of 20 J/cm 2 was produced which is the equivalent to two standard epithelial doses or 30 min exposure to sunlight at noon on a sunny day in Southern Europe (Liu et al, 2014). This dose of UV-A light has been shown to significantly increase plasma nitrite immediately after irradiation with values remaining elevated at least 40 min after exposure (Liu et al, 2014). During SHAM trials an aluminum foil space blanket covered participants, blocking UV-A radiation reaching the skin whilst allowing surface and body temperature to rise (Liu et al, 2014).…”

“…This dose of UV-A light has been shown to significantly increase plasma nitrite immediately after irradiation with values remaining elevated at least 40 min after exposure (Liu et al, 2014). During SHAM trials an aluminum foil space blanket covered participants, blocking UV-A radiation reaching the skin whilst allowing surface and body temperature to rise (Liu et al, 2014). Participants were aware of the significance of the aluminum space blanket prior to the start of the study.…”

Vitamin D as a novel therapy in inflammatory bowel disease: new hope or false dawn?

“…Although newer theories suggest that other components of sunlight (e.g. UVA non-vitamin D-making rays) might also have health effects, independent of vitamin D (33) . The association with disease incidence and latitude is not unique to IBD; there is supporting parallel evidence of a north-south gradient in the incidence of other autoimmune and gastrointestinal diseases, including rheumatoid arthritis (34) and colorectal cancer (35)(36)(37) .…”