PHYSIOLOGICAL EFFECTS OF DIETARY SODIUM IN SALT RESISTANT HUMANS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Recent evidence suggests that sodium may contribute to structural and functional abnormalities, independent of blood pressure (BP). Specifically, data in experimental animals suggest that sodium-loading  independent of changes in BP  promotes cardiac, vascular, and renal damage. Deleterious physiological changes from excess sodium have been documented in spontaneously hypertensive rats, and  with particular relevance for this proposal  in normotensive Wistar-Kyoto rats. In short, there is a growing appreciation that elevated BP is not the only problem related to excess dietary sodium. The objective of this INBRE proposal is to build upon these animal studies by exploring these issues in humans; these mechanistic animal studies need to be translated to human studies. We will examine the physiological effects of dietary sodium in a group that we characterize as having salt resistant BP ( 5 mmHg change in mean BP going from a low to high sodium diet). Subjects will complete a 17-day dietary trial (3-day run-in of 100 mmol/day of sodium, 7 days high sodium (350 mmol/day) and 7 days of low sodium (20 mmol/day). All foods will be prepared for the subjects thought an established collaboration with Christiana Care Health System. Dietary compliance will be assessed by collecting 24 hours of urine on the last day of each condition; salt sensitivity of BP will be individually assessed via 24-hour ambulatory BP on the last day of each condition. Our overall hypothesis is that dietary sodium will adversely affect circadian BP rhythm, arterial function, and venous function. Circadian BP rhythm will be assessed using the night time dip in pressure; arterial function will be assessed via pulse wave velocity and augmentation index; endothelial function will be assessed via brachial flow-mediated dilation; and venous function will be assess via venous occlusion plethysmography. The strength of this proposal is the sophisticated physiological assessment that will be performed under well-controlled dietary conditions in a group that does not have "salt sensitive" BP. Habitual sodium intake is high in the general population, therefore our focus will be on demonstrating differences in these variables between the high and low sodium conditions. This proposal brings together a multi-disciplinary team which includes individuals from Physiology, Cardiology, Medical Technology, Nutrition, and Nursing. Two different institutions in the state of Delaware are involved (University of Delaware and Christiana Care Health System). This team represents a true collaborative partnership. This proposal will also provide hands-on research experience for undergraduate and graduate students. The data collected under this funding mechanism will form the basis of an R01 submission.