Whole body UVA irradiation lowers systemic blood pressure by release of nitric oxide from intracutaneous photolabile nitric oxide derivates.

RATIONALE Human skin contains photolabile nitric oxide derivates like nitrite and S-nitroso thiols, which after UVA irradiation, decompose and lead to the formation of vasoactive NO. OBJECTIVE Here, we investigated whether whole body UVA irradiation influences the blood pressure of healthy volunteers because of cutaneous nonenzymatic NO formation. METHODS AND RESULTS As detected by chemoluminescence detection or by electron paramagnetic resonance spectroscopy in vitro with human skin specimens, UVA illumination (25 J/cm(2)) significantly increased the intradermal levels of free NO. In addition, UVA enhanced dermal S-nitrosothiols 2.3-fold, and the subfraction of dermal S-nitrosoalbumin 2.9-fold. In vivo, in healthy volunteers creamed with a skin cream containing isotopically labeled (15)N-nitrite, whole body UVA irradiation (20 J/cm(2)) induced significant levels of (15)N-labeled S-nitrosothiols in the blood plasma of light exposed subjects, as detected by cavity leak out spectroscopy. Furthermore, whole body UVA irradiation caused a rapid, significant decrease, lasting up to 60 minutes, in systolic and diastolic blood pressure of healthy volunteers by 11+/-2% at 30 minutes after UVA exposure. The decrease in blood pressure strongly correlated (R(2)=0.74) with enhanced plasma concentration of nitrosated species, as detected by a chemiluminescence assay, with increased forearm blood flow (+26+/-7%), with increased flow mediated vasodilation of the brachial artery (+68+/-22%), and with decreased forearm vascular resistance (-28+/-7%). CONCLUSIONS UVA irradiation of human skin caused a significant drop in blood pressure even at moderate UVA doses. The effects were attributed to UVA induced release of NO from cutaneous photolabile NO derivates.