Menstrual cycle and sex effects on sympathetic responses to acute chemoreflex stress

Abstract

This study aimed to examine the effects of sex (males vs. females) and sex hormones (menstrual cycle phases in women) on sympathetic responsiveness to severe chemoreflex activation in young, healthy individuals. Muscle sympathetic nerve activity (MSNA) was measured at baseline and during rebreathing followed by a maximal end-inspiratory apnea. In women, baseline MSNA was greater in the midluteal (ML) than early-follicular (EF) phase of the menstrual cycle. Baseline MSNA burst incidence was greater in men than women, while burst frequency and total MSNA were similar between men and women only in the ML phase. Chemoreflex activation evoked graded increases in MSNA burst frequency, amplitude, and total activity in all participants. In women, this sympathoexcitation was greater in the EF than ML phase. The sympathoexcitatory response to chemoreflex stimulation of the EF phase in women was also greater than in men. Nonetheless, changes in total peripheral resistance were similar between sexes and menstrual cycle phases. This indicates that neurovascular transduction was attenuated during the EF phase during chemoreflex activation, thereby offsetting the exaggerated sympathoexcitation. Chemoreflex-induced increases in mean arterial pressure were similar across sexes and menstrual cycle phases. During acute chemoreflex stimulation, reduced neurovascular transduction could provide a mechanism by which apnea-associated morbidity might be attenuated in women relative to men.

Sex hormone effects on autonomic and endothelial function

“…The authors point out that few investigations have considered the effects of sex on sympathetic responses to chemoreflex stimulation, with studies either excluding women or not considering sex as a variable. Generally, differences in the chemoreflex between the sexes are less apparent than differences due to sex hormones within women during the course the menstrual cycle or while taking hormonal contraceptives (Usselman et al 2015), suggesting an interaction between sex hormone Introduction exposure and the chemoreflex in young women. Further, changes occur during pregnancy and ageing.…”

Effects of one's sex and sex hormones on sympathetic responses to chemoreflex activation

“…Owing to the multifaceted nature of the chemoreflex stimulus used in our study (Usselman et al . a ), we were unable to determine whether the sex difference in sympathetic activation lies in the response to hypoxia, hypercapnia or the cessation of breathing. In a previous study examining sympathetic activation during 10 min of isocapnic hypoxia in young healthy men and women, Jones et al .…”

“…While sympathetic nerve activity is influenced by a number of factors, we have provided evidence of altered chemoreflex‐driven activation of sympathetic nerve activity related to acute variations in circulating sex hormones (Usselman et al . , a ). As such, this article reviews the literature regarding the role for sex hormones in cardiovascular responses to chemoreflex activation with particular focus on effects within the sympathetic nervous system as assessed directly through the measurement of muscle sympathetic nerve activity (MSNA).…”

“…Recently, we examined the effect of sex on chemoreflex regulation of MSNA in young healthy men and women who were not using any form of hormonal contraception (Usselman et al . a ). In this study, a rebreathing task was performed before a maximal voluntary end‐inspiratory apnoea to create to a potent hypercapnic–hypoxic stimulus.…”

“…In these studies, MSNA and haemodynamic responses to a multifaceted chemoreflex stimulus (hypoxic–hypercapnic maximal end‐inspiratory apnoea, described in the previous section) were compared throughout the menstrual cycle (Usselman et al . a ) and between phases of hormonal contraceptive use (Usselman et al . ).…”