The effects of sex and ovarian hormones on arterial baroreflex control of blood pressure in humans

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The arterial baroreceptors are responsible for mediating rapid reflex adjustments to acute cardiovascular stressors via modulating autonomic nervous system activity to the heart and vasculature. Alterations in the arterial baroreflex control of blood pressure (e.g. decreased sensitivity) have been recognized to potentially contribute to differences in blood pressure control between young men and women. In this work we investigated whether sex differences exist in arterial blood pressure responses to baroreceptor perturbation, and differential mechanisms for the relative contribution of cardiac output and total vascular conductance to baroreflex-mediated changes in blood pressure in young women and men, both at rest and during dynamic exercise. Here we demonstrated that sex differences in the baroreflex control of blood pressure are evident during carotid hypertension, but not carotid hypotension. Furthermore, young women exhibit greater depressor responses to carotid hypertension by virtue of a greater cardiac responsiveness (manifest as a cardiac output response) independent of menstrual cycle phases at rest. During exercise, however, cardiac output is no longer the main mechanism to control blood pressure in women due to greater metabolic demand to contracting skeletal muscles. In conclusion, this dissertation project provides novel insight into understanding influences of sex and endogenous ovarian hormones on arterial baroreflex control of blood pressure, and investigated mechanisms by which the baroreflex-mediated blood pressure response is controlled at rest and during dynamic exercise. This project suggests that fundamental mechanisms of sex differences exist in blood pressure regulation.