Renal Sensory Nerve Contribution to Hypertension

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PROJECT SUMMARY/ABSTRACT: High blood pressure is a leading cause of morbidity and mortality worldwide and greatly contributes to a multitude of cardiovascular disease. Although the renal sympathetic nerves have been the focus of many basic and clinical studies, the role of the renal afferent (sensory) nerves in mediating hypertension remains poorly understood. Activation of renal afferents can potentially either excite or inhibit global sympathetic nerve activity and thereby increase or decrease blood pressure, but the precise mechanisms controlling the balance of the excitatory vs. inhibitory reflex actions of the renal afferent nerves are currently unknown. We have recently determined that the endothelin-1 (ET-1) system significantly modulates renal afferent nerves. Our central hypothesis is that endothelin A (ETA) receptor activation on renal afferent nerves increases sympathetic nerve activity and blood pressure, and that endothelin B (ETB) receptor activation on renal afferent nerves decreases sympathetic nerve activity and blood pressure. We will test this hypothesis using rodent models in the settings of both normal physiology and hypertension. ETA or ETB receptors on renal nerves will be directly activated in rats instrumented with radiotelemetry devices, which allow for recording of blood pressure and markers of sympathetic nerve activity in unrestrained, conscious animals. These experiments, which will also include in vitro culturing, imaging, and electrophysiological examination of renal afferent nerves will provide important new information about the mechanisms of afferent nerve activation. High salt and high fat content are common features of the typical Western diet and are well-known to play a role in the development of many cardiovascular diseases such as hypertension. Our preliminary evidence indicates that these factors also increase renal afferent nerve expression of ET-1 and ETA receptors. Because of this connection to increases in abberant renal afferent nerve activity and blood pressure, we will also test the hypothesis that high salt or high fat diet increases afferent nerve ET-1 expression and a preponderance of ETA to ETB receptor signaling promoting increased afferent nerve activity, sympathetic tone, and blood pressure. This hypothesis will be tested through the use of rat models with specific pharmacological inhibition of ETA and/or ETB receptors on renal afferent nerves, and animals will be fed a high salt or high fat diet. Together, these studies will provide a mechanistic understanding of how excitation versus inhibition of renal afferent nerves contributes to hypertension and thus could lead to specific and efficient therapeutic interventions for the treatment of hypertension. This research study and the proposed mentored training plan will provide the applicant with the specific scientific training needed for successful transition into independence.