title: Hormone phase influences sympathetic responses to high levels of lower body negative pressure in young healthy women.
abstract: We tested the hypothesis that sympathetic responses to baroreceptor unloading may be affected by circulating sex hormones. During lower body negative pressure at -30, -60, and -80 mmHg, muscle sympathetic nerve activity (MSNA), heart rate, and blood pressure were recorded in women who were taking (n = 8) or not taking (n = 9) hormonal contraceptives. All women were tested twice, once during the low-hormone phase (i.e., the early follicular phase of the menstrual cycle and the placebo phase of hormonal contraceptive use), and again during the high-hormone phase (i.e., the midluteal phase of the menstrual cycle and active phase of contraceptive use). During baroreceptor unloading, the reductions in stroke volume and resultant increases in MSNA and total peripheral resistance were greater in high-hormone than low-hormone phases in both groups. When normalized to the fall in stroke volume, increases in MSNA were no longer different between hormone phases. While stroke volume and sympathetic responses were similar between women taking and not taking hormonal contraceptives, mean arterial pressure was maintained during baroreceptor unloading in women not taking hormonal contraceptives but not in women using hormonal contraceptives. These data suggest that differences in sympathetic activation between hormone phases, as elicited by lower body negative pressure, are the result of hormonally mediated changes in the hemodynamic consequences of negative pressure, rather than centrally driven alterations to sympathetic regulation.
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada.
authors.forename: Charlotte W
authors.initials: CW
authors.lastname: Usselman
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada.
authors.forename: Chantelle A
authors.initials: CA
authors.lastname: Nielson
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada.
authors.forename: Torri A
authors.initials: TA
authors.lastname: Luchyshyn
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada.
authors.forename: Tamara I
authors.initials: TI
authors.lastname: Gimon
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada.
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Coverdale
authors.affiliation: Department of Medicine, Western University, London, Ontario, Canada.|Lawson Health Research Institute, Western University, London, Ontario, Canada; and.
authors.forename: Stan H M
authors.initials: SH
authors.lastname: Van Uum
authors.affiliation: Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada; kshoemak@uwo.ca.|Department of Physiology and Pharmacology, Western University, London, Ontario, Canada.
authors.forename: J Kevin
authors.initials: JK
authors.lastname: Shoemaker
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D003278:Contraceptives, Oral, Hormonal / Q000008:administration & dosage / Q000494:pharmacology; D005260:Female; D005498:Follicular Phase / Q000187:drug effects / Q000502:physiology; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008150:Lower Body Negative Pressure; D008183:Luteal Phase / Q000187:drug effects / Q000502:physiology; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000000981:diagnostic imaging / Q000502:physiology*
chemical_list: D003278:Contraceptives, Oral, Hormonal; D012739:Gonadal Steroid Hormones
keywords: baroreceptor unloading; hormonal contraceptives; menstrual cycle; muscle sympathetic nerve activity; sex hormones