HIGHLIGHTED TOPIC Hypoxia Sex and vasodilator responses to hypoxia at rest and during exercise

Casey DP, Shepherd JR, Joyner MJ. Sex and vasodilator responses to hypoxia at rest and during exercise. J Appl Physiol 116: 927–936, 2014. First published July 3, 2013; doi:10.1152/japplphysiol.00409.2013.—In humans, -adrenergic receptor activation causes a substantial portion of hypoxic vasodilation in skeletal muscle at rest and during forearm exercise. Recent evidence suggests that -adrenergic receptors are either more sensitive or upregulated in young women vs. men. Therefore, we examined whether sex influences hypoxic vasodilation in 31 young subjects (15 women/16 men; 26 1 yr). We also examined whether potential sex-related differences existed in a group of older adults (6 women/5 men; 61 2 yr). All subjects performed forearm exercise at 10 and 20% of maximum under normoxic and hypoxic [80% arterial O2 saturation (SO2)] conditions. Forearm vascular conductance (FVC; ml·min ·100 mmHg ) was calculated from blood flow (ml/min) and blood pressure (mmHg). At rest, young women demonstrated a greater vasodilator response to hypoxia compared with men (39 12 vs. 13 6%, P 0.05). The absolute compensatory vasodilator response (hypoxic FVC-normoxic FVC) during exercise was similar between sexes, but the relative change was greater in young women at 10% (28 5 vs. 17 3%, P 0.05) and 20% exercise (29 4% vs. 15 3%, P 0.01). Additionally, the absolute changes in vasodilation after normalizing the response to forearm volume or workload were greater in young women during exercise (P 0.05). Interestingly, the compensatory vasodilator responses between older women and men were similar at 10 and 20% exercise, regardless of whether the response is expressed as absolute, relative, or absolute change normalized for forearm volume or workload (P 0.054–0.97). Our data suggest that the compensatory vasodilator response to hypoxic exercise is greater in young women compared with men. However, sex-specific differences appear to be lost with aging.