Gonadal hormones may affect homeostatic mechanisms regulating the cardiovascular system. We investigated this relationship at five different crucial hormonal time points along the menstrual cycle. Eight eumenorrheic healthy subjects underwent a battery of autonomic tests, hemodynamics, and volume-regulatory hormone measurements. Fluid-regulatory hormones, plasma renin activity, and aldosterone increased along the luteal phase (P = 0.003 and 0.02, respectively), whereas rest supine-corrected hematocrit declined in the course of the menstrual cycle (P = 0.001). Plasma norepinephrine decreased from 1.4 +/- 0.2 to 0.95 +/- 0.1 nmol/liter (P < 0.02) [early follicular (EF) to late follicular]. Thereafter, concentrations gradually returned to EF levels. Lf to Hf domain ratio (spectral analysis of electrocardiogram) showed a difference from that of norepinephrine. The cardiovagal baroreflex sensitivity increased significantly along the luteal phase (P = 0.04). The dose of isoproterenol required to increase heart rate (HR) 15 beats per minute was 0.19 +/- 0.04 microg during the EF time point, and it increased to 0.39 +/- 0.06 microg during the late luteal time point (P = 0.05). However, blood pressure, HR, and their responses to orthostatic stress remained unchanged. Fluctuations in the ovarian hormones along the menstrual cycle are associated with unchanged blood pressure and HR, despite the significant variations in the different homeostatic mechanisms regulating the cardiovascular system.