Exposing human skin to 20 J·cm2 of ultraviolet-A (UV-A) light has been shown to release nitric oxide (NO) species from dermal storage forms and mildly reduce blood pressure (BP). The dose-response relationship of these effects, however, remains unknown.PURPOSE: To determine the effects of two different doses of UV-A light on NO metabolites, mean arterial pressure (MAP) and resting energy expenditure (REE).METHODS: Eight healthy males (age: 28 ± 5 yr, body mass: 81 ± 12 kg) were exposed to three light conditions in a randomised counter-balanced order. Following at least 30 min of supine rest, participants were exposed to either (i) no light (CON) (ii) 10 J·cm2 UV-A light (UVA10), or (iii) 20 J·cm2 UV-A light (UVA20). UVA20 is comparable to 30 min of sunshine in southern Europe in summer. During the experiment oxygen consumption (VO2) and REE were monitored continuously using indirect calorimetry. Regular BP measurements were taken and samples of venous blood collected before and after light exposure. Plasma nitrate [NO3-] and nitrite [NO2-] were later analysed via HPLC (n=7). Statistical differences are reported together with effect sizes (Cohen’s d) where appropriate.RESULTS: There were no significant changes in plasma [NO3-] or [NO2-] between pre- and post-exposures in all conditions (P>0.05). Plasma [NO2-] was moderately higher after UVA20 exposure compared to CON (Δ 29%, 178 ± 299 nM, d=0.58, P=0.17) but increased to only a small extent with UV10 (Δ 9%, 58 ± 220 nM, d=0.26, P=0.51). There were no differences in MAP between conditions or before and after exposure (both P>0.50). There was a marked decline in REE following UVA20 (Δ 7%, 112 ± 143 kcal/day, d=0.78, P<0.01) and UV10 (Δ 4% 134± 159 kcal/day, d=0.84, P=0.07) while no significant differences were observed in the CON group (P=1.0). From pre- to post-light exposure, VO2 declined with UVA20 (Δ 6%, 13 ± 19 ml/min, P=0.04), but did not change with UVA10 (P=0.26) or CON (P=0.44).CONCLUSION: The present data suggests that a 20 J·cm2 dose of UV-A light increases [NO2-] and decreases REE and VO2 to a greater extent than 10 J·cm2. Although speculative, it is probable that reductions in REE and VO2 were mediated by an increased NO availability. Neither dose of UV-A light resulted in a detectable change in BP although a larger sample is required before definitive conclusions can be made.
|Journal||Medicine & Science in Sports & Exercise|
|Publication status||Published - May 2016|