Although muscle sympathetic activity and the sensitivity of the sympathetic baroreflex vary throughout the menstrual cycle in healthy subjects (Minson et al., 2000), Fu et al. found that the plasma catecholamine response to standing remained unchanged during the phase of the menstrual cycle but noted an association between incidence of presyncope and reduced plasma renin activity and aldosterone levels in the early follicular phase of the menstrual cycle in patients with POTS (Fu et al., 2010). Here, REN is linked to postural orthostatic tachycardia syndrome.