Medical

UVA lowers blood pressure and vasodilates the systemic arterial vasculature by mobilisation of cutaneous nitric oxide stores

From http://www.nature.com/jid/journal/v133/n1s/full/jid2013104a.html

Journal of Investigative Dermatology

1247

UVA lowers blood pressure and vasodilates the systemic arterial vasculature by mobilisation of cutaneous nitric oxide stores

(Me Translated: Some types of sunlight lower blood pressure and expands blood vessels by using nitric oxide.)

D Liu,1 BO Fernandez,3 NN Lang,2 JM Gallagher,4 DE Newby,2 M Feelisch3 and RB Weller1,5 1Dermatology, University of Edinburgh, Edinburgh, United Kingdom, 2Cardiology, University of Edinburgh, Edinburgh, United Kingdom, 3Medicine, University of Southampton, Southampton, United Kingdom, 4Leithmount Surgery, Edinburgh, United Kingdom and 5Centre for Inflammation Research, University of Edinburgh, Edinburgh, United Kingdom

The incidence of hypertension and cardiovascular disease (CVD) correlates with latitude and rises in winter. Population vitamin D levels inversely correlate with CVD, but oral supplementation does not alter CVD rates. Skin contains large stores of nitrite(NO2) and nitrate(NO3). Nitrate is biologically inert, but can be photo-reduced to active NO2 and nitric oxide (NO). The dermal vasculature enables rapid systemic dispersal of NO2 and NO.We hypothesised that ultraviolet A (UVA) mobilises NO bioactivity from skin to circulation to exert beneficial cardiovascular effects. Vit’ D is a marker for sunlight exposure. 24 healthy volunteers were sham (temp’ control) irradiated then actively irradiated with 20 J/cm2 UVA. Mean arterial pressure (MAP) fell and heart rate rose during active but not sham irrad’n (3.50±0.73 mmHg vs 2.80±0.98). The MAP fall was sustained for 50 mins in the active group only. Temperature rise was the same in both groups. Circulatory nitrite rose (0.50±0.04 μM to 0.72±0.04 μM p<0.001) and nitrate fell (11.79± 0.64 μM to 8.99±0.40 μM (p<0.001)) during active, but not sham irradiation. There was no change in circulating vitamin D levels. 12 volunteers had forearm blood flow (FBF) measured by venous plethysmography while 8 μmol/min of the NOS antagonist L-NMMA was infused to the brachial artery. FBF rose during active but not sham irradiation (23.7±6.5 % over baseline vs no change p<.0002). Physiological levels of UVA irradiation cause systemic vasodilation and lower BP in a vitamin D and NOS independent manner. Deaths from CVD and stroke are 60 to 100 times higher than from skin cancers in northern Europe. This study provides a mechanistic explanation for the inverse correlation between sunlight exposure and CVD mortality. Sunlight has beneficial effects independently of vitamin D synthesis.

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