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

The individual effects of estrogen and progesterone on baroreflex function remain poorly understood. We sought to determine how estradiol (E-2) and progesterone (P-4) independently alter the carotid-cardiac and carotid-vasomotor baroreflexes in young women by using a hormone suppression and exogenous add-back design. Thirty-two young women were divided into two groups and studied under three conditions: 1) after 4 days of endogenous hormone suppression with a gonadotropin releasing hormone antagonist (control condition), 2) after continued suppression and 3 to 4 days of supplementation with either 200 mg/day oral progesterone (N = 16) or 0.1 to 0.2 mg/day transdermal 17 beta-estradiol (N = 16), and 3) after continued suppression and 3 to 4 days of supplementation with both hormones. Changes in heart rate (HR), mean arterial pressure (MAP), and femoral vascular conductance (FVC) were measured in response to 5 s of +50 mmHg external neck pressure to unload the carotid baroreceptors. Significant hormone effects on the change in HR, MAP, and FVC from baseline at the onset of neck pressure were determined using mixed model covariate analyses accounting for P-4 and E-2 plasma concentrations. Neither P-4 (P = 0.95) nor E-2 (P = 0.95) affected the HR response to neck pressure. Higher P-4 concentrations were associated with an attenuated fall in FVC (P = 0.01), whereas higher E-2 concentrations were associated with an augmented fall in FVC (P = 0.02). Higher E-2 was also associated with an augmented rise in MAP (P = 0.01). We conclude that progesterone blunts whereas estradiol enhances carotid-vasomotor baroreflex sensitivity, perhaps explaining why no differences in sympathetic baroreflex sensitivity are commonly reported between low and high combined hormone phases of the menstrual cycle.