title: Does the menstrual cycle influence the sensitivity of vagally mediated baroreflexes?
abstract: The menstrual cycle provokes several physiological changes that could influence autonomic regulatory mechanisms. We studied the carotid-cardiac baroreflex in ten healthy young women on four occasions over the course of their menstrual cycles (days 0-8, 9-14, 15-20 and 21-25). We drew blood during each session for analysis of oestrogen, progesterone and noradrenaline (norepinephrine) levels, and assessed carotid-cardiac baroreflex function by analysing R-R interval responses to graded neck pressure sequences. Oestrogen levels followed a classical two-peak (cubic) response, with elevated levels on days 9-14 and 21-25 compared with days 0-8 and 15-20 (P=0.0032), while progesterone levels increased exponentially from days 9-14 to days 21-25 (P=0.0063). Noradrenaline levels increased from an average of 137 pg/ml during the first three measurement periods to 199 pg/ml during days 21-25 (P=0.0456). Carotid-cardiac baroreflex gain and operational point were not statistically different at any of the time points during the menstrual cycle (P> or =0.18). These findings are consistent with the notion that beat-to-beat vagal-cardiac regulation does not change over the course of the normal menstrual cycle.
authors.affiliation: Department of Biomedical Engineering, Michigan Technological University, Houghton 49931, USA. whcooke@mtu.edu
authors.forename: William H
authors.initials: WH
authors.lastname: Cooke
authors.forename: David A
authors.initials: DA
authors.lastname: Ludwig
authors.forename: Paul S
authors.initials: PS
authors.lastname: Hogg
authors.forename: Dwain L
authors.initials: DL
authors.lastname: Eckberg
authors.forename: Victor A
authors.initials: VA
authors.lastname: Convertino
mesh_terms: D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D004967:Estrogens / Q000097:blood; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008597:Menstrual Cycle / Q000502:physiology*; D009638:Norepinephrine / Q000097:blood; D011374:Progesterone / Q000097:blood; D014630:Vagus Nerve / Q000502:physiology*
chemical_list: D004967:Estrogens; D011374:Progesterone; D009638:Norepinephrine