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Abstract
Cardiovascular events and death rates are highest during the winter months. Endothelial dysfunction, characterized by reduced nitric oxide (NO) bioavailability, is a non-traditional risk factor for cardiovascular disease (CVD) that typically precedes the development of hypertension and increases cardiovascular risk. Exaggerated blood pressure (BP) responses to physiological stressors could potentiate this risk. Therefore, we assessed 15 young, healthy (23 ± 2; 7 men, 8 women) adults in the summer/early-fall and winter/early-spring to determine if there were seasonal variations in endothelial function and BP control. Intradermal microdialysis coupled with a standard local heating (42⁰C) protocol and flow-mediated dilation (FMD) measured endothelial function. Continuous blood pressure measurement (finger photoplethysmography) measured BP responses to a 3-min hand cold pressor test (CPT). Mean daytime (sunrise to sunset) ambient temperature, wet bulb globe temperature (WBGT), and UV index were recorded the 30 days prior to experimental visits. Serum vitamin D concentrations [25(OH)D] were measured at each visit. Winter/early-spring FMD was not different (P = 0.54), but %NO contribution to local heating was attenuated (41.89 ± 15.11 vs. 67.41 ± 10.32 %, P = 0.0003) compared to summer/early-fall. WBGT was positively associated with the %NO contribution to local heating (P = 0.01, r = 0.52), but UV and [25(OH)D] were not related. There were no seasonal variations in peak BP responses to the CPT [SBP (P = 0.33), DBP (P = 0.47), and MAP (P = 0.39)]. Young, healthy, adults exhibit attenuated NO-mediated cutaneous vasodilation in the winter/early-spring, which may be partially mediated by decreased WBGT.