Effect of sex and ovarian hormones on carotid baroreflex resetting and function during dynamic exercise in humans

Abstract

Kim A, Deo SH, Fisher JP, Fadel PJ. Effect of sex and ovarian hormones on carotid baroreflex resetting and function during dynamic exercise in humans. J Appl Physiol 112: 1361-1371, 2012. First published January 19, 2012 doi:10.1152/japplphysiol.01308.2011.-To date, no studies have examined whether there are either sex-or ovarian hormone-related alterations in arterial baroreflex resetting and function during dynamic exercise. Thus we studied 16 young men and 18 young women at rest and during leg cycling at 50% heart rate (HR) reserve. In addition, 10 women were studied at three different phases of the menstrual cycle. Five-second pulses of neck pressure (NP) and neck suction (NS) from ϩ40 to Ϫ80 Torr were applied to determine full carotid baroreflex (CBR) stimulus response curves. An upward and rightward resetting of the CBR function curve was observed during exercise in all groups with a similar magnitude of CBR resetting for mean arterial pressure (MAP) and HR between sexes (P Ͼ 0.05) and at different phases of the menstrual cycle (P Ͼ 0.05). For CBR control of MAP, women exhibited augmented pressor responses to NP at rest and exercise during mid-luteal compared with early and late follicular phases. For CBR control of HR, there was a greater bradycardic response to NS in women across all menstrual cycle phases with the operating point (OP) located further away from centering point (CP) on the CBR-HR curve during rest (OP-CP; in mmHg: Ϫ13 Ϯ 3 women vs. Ϫ3 Ϯ 3 men; P Ͻ 0.05) and exercise (in mmHg: Ϫ31 Ϯ 2 women vs. Ϫ15 Ϯ 3 men; P Ͻ 0.05). Collectively, these findings suggest that sex and fluctuations in ovarian hormones do not influence exercise resetting of the baroreflex. However, women exhibited greater CBR control of HR during exercise, specifically against acute hypertension, an effect that was present throughout the menstrual cycle. arterial baroreceptors; blood pressure; gender; estradiol; progesterone; menstrual cycle THE ARTERIAL BAROREFLEX (ABR) plays an important role in beat-to-beat control of blood pressure (BP) via modulating autonomic neural activity to the heart and vasculature (46, 47). The ABR is reset during dynamic exercise partly due to the actions and interactions of two neural mechanisms, namely central command (feedforward signals from higher brain centers) and the exercise pressor reflex (feedback signals from contracting skeletal muscles) (14,19,20,32,46,47). Moreover, the ABR, together with central command and the exercise pressor reflex play an essential role in evoking appropriate neural cardiovascular responses to exercise. Indeed, sinoaortic denervation and reductions in ABR control have been shown to lead to exaggerated elevations in BP upon exercise (6,56,57). Thus appropriate ABR resetting and function are requisite for normal BP responses to dynamic exercise (14,26,46,47).Young men tend to exhibit greater pressor responses to exercise compared with age-matched women (7,12,29,38); however, the reason for these differences remains unclear. Interestingly, studies have shown tha...

Short-term administration of progesterone and estradiol independently alter carotid-vasomotor, but not carotid-cardiac, baroreflex function in young women

“…It is possible differences in techniques for measuring cardiac baroreflex sensitivity account for the disparity in findings. Studies using the neck pressure technique have shown no differences in sensitivity across the menstrual cycle (8,24), consistent with our results. We are the first to assess progesterone independently.…”

“…Previous studies have used a range of both neck pressure and neck suction to assess carotid baroreflex sensitivity and construct full baroreflex curves (24,35,37). We only assessed the responses to ϩ50 mmHg of neck pressure.…”

“…One study recently used external neck pressure to examine differences in baroreflex sensitivity across the early follicular, ovulatory, and mid-luteal phases of the menstrual cycle (24). The study found no differences in the response of HR across phases, but researchers did observe an augmented increase in mean arterial pressure (MAP) to neck pressure during the mid-luteal phase when both estrogen and progesterone are high compared with the early-follicular and ovulatory phases.…”

New insights into the effects of age and sex on arterial baroreflex function at rest and during dynamic exercise in humans

“…However, cardiac ABR sensitivity has been reported to be increased during the late follicular phase compared with the early follicular and mid-luteal phases of the menstrual cycle (Tanaka et al, 2003). We recently used the variable pressure neck chamber technique to derive full carotid baroreflex stimulus-response curves in an attempt to better understand whether sex and/or fluctuations in endogenous ovarian hormones during the menstrual cycle modulate carotid baroreflex control of the heart (Kim et al, 2012). We noted a greater bradycardic response to carotid baroreceptor loading (i.e., simulated carotid hypertension) in young women at the early follicular phase of the menstrual cycle compared to young men.…”

Yes! Sex Matters: Sex, the Brain and Blood Pressure

“…Sex differences in baroreceptor reflex function have been reported in humans [28], [29], [27]. Young women have been shown to have lower resting sympathetic outflow and enhanced baroreflex function as compared to age matched men [30].…”