1 Limberg , et al . 1 1 2 3 Alpha - Adrenergic Control of Blood Flow during Exercise : Effect of Sex and 4 Menstrual Phase 5

32 33 Sex differences exist in autonomic control of the cardiovascular system. This study was 34 designed to directly test sex or female menstrual phase-related differences in α35 adrenergic control of blood flow during exercise. We hypothesized that women would 36 exhibit reduced α-adrenergic vasoconstriction when compared to men during exercise; 37 in addition, women would constrict less during the early luteal than the early follicular 38 phase of the female menses. Young men (n=10) were studied once and women (n=9) 39 were studied twice; once during the early follicular phase and once during the early 40 luteal phase of female menses. We measured forearm blood flow (Doppler Ultrasound 41 of the brachial artery) during rest and steady-state dynamic exercise (15% and 30% of 42 maximal voluntary contraction; 20 contractions/min). A brachial artery catheter was 43 inserted for the local administration of α-adrenergic agonists [phenylephrine (PE, α1) or 44 clonidine (CL, α2)]. Blood flow responses to exercise (forearm vascular conductance, 45 FVC) were similar between all groups. At rest, infusion of PE or CL decreased FVC in 46 all groups (40-60% reduction). Vasoconstriction to PE was abolished in all groups at 47 15% and 30% exercise intensity. Vasoconstriction to CL was reduced at 15% and 48 abolished at 30% intensity in all groups; women had less CL-induced constriction during 49 the early luteal than early follicular phase (p<0.017, 15% intensity). These results 50 indicate vasodilator responses to forearm exercise are comparable between men and 51 women and are achieved through similar paths of α-adrenergic vascular control at 52 moderate intensities; this control may differ at low intensities, specific to the female 53