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lundi 15 juillet 2013

Don't miss the sun exposure!

UVA lowers blood pressure and vasodilates the systemic arterial vasculature by mobilisation
of cutaneous nitric oxide stores
D Liu,1 BO Fernandez,3 NN Lang,2 JM Gallagher,4 DE Newby,2 M Feelisch3 and RB Weller1,5 1
Dermatology, University of Edinburgh, Edinburgh, United Kingdom, 2 Cardiology, University
of Edinburgh, Edinburgh, United Kingdom, 3 Medicine, University of Southampton,
Southampton, United Kingdom, 4 Leithmount Surgery, Edinburgh, United Kingdom and 5
Centre 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="" 0.64="" 8.99="" and="" during="" fell="" font="" nitrate="" p="" to="">
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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