Sympathetic baroreflex control and vascular transduction in African Americans

University Of Texas Arlington, Arlington TX

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Abstract

? DESCRIPTION (provided by applicant): African Americans (AA) are at high risk for the development of hypertension, with ~44% of the AA adult population being affected. Hypertension-related deaths account for ~20% of all deaths within this population in the United States, twice that of their Caucasian American (CA) counterparts. In addition to these chronic blood pressure data, as well as increased risk for death associated with hypertension in AA (e.g., stroke, end-stage renal disease, etc.), several investigations have demonstrated physiological differences in response to acute pressor stimuli between otherwise normotensive AA and CA. We recently demonstrated impaired baroreflex control of heart rate at rest in otherwise healthy, non-hypertensive AA, compared to CA. In addition, the impaired baroreflex-cardiac function persisted during steady-state exercise, while reduced baroreflex control of blood pressure became apparent. While our recent publications support inherent differences in dynamic blood pressure regulation in AA both at rest and during exercise, understanding the control of sympathetic nerve activity and associated vascular responses in AA is of key importance since the control of peripheral vascular resistance (via the sympathetic nervous system) accounts for ?70% of baroreflex mediated blood pressure responses. Novel and exciting preliminary data further support the need to pursue these studies. The goal of this proposal is to test hypotheses in three areas: 1) impaired arterial baroreflex control of muscle sympathetic nerve activity at rest and during exercise in AA, 2) exaggerated sympatho-vascular transduction at rest and during exercise in AA, and 3) the role of family history of hypertension on the aforementioned neural vascular mechanisms. These studies will be performed in non-hypertensive AA men and women compared to age, sex, body mass, and fitness-matched CA counterparts. Both pharmacological (modified Oxford) and non-invasive (neck chamber) techniques will be utilized to investigate arterial baroreflex (and isolated carotid baroreflex) function at rest and during steady-state exercise. Furthermore, the transduction of muscle sympathetic nerve activity to vascular responses (i.e., sympathetically-mediated vasoconstriction) will be examined using microneurography (sympathetic nerve activity), duplex Doppler ultrasound (limb blood flow) and continuous arterial pressure (for calculated conductance). Findings from the proposed work will provide important information related to arterial blood pressure control in AA, a population that is at high risk for the development of hypertension. Furthermore, these studies will elucidate the role of primary blood pressure control mechanisms (i.e., neural and vascular components), improving the understanding of blood pressure regulation in AA and provide important insight in this population (as well as in CA). In addition, these findings will provide data for the investigation of genetic differences (e.., polymorphisms) related to the development of hypertension with attention to the interaction between sympathetic nerve activity, baroreflex function and the vasculature in AA.