Abstract 32: A Rapid Method for Clinical Diagnosis of Salt Sensitivity of Blood Pressure
Salt-sensitivity of blood pressure (BP) is a cardiovascular risk that affects 25% of the world’s population due to its resulting hypertension, although independent of BP. Salt-sensitivity is detected with a two week controlled diet, which is difficult to administer in the clinical setting. We therefore developed a rapid method of diagnosis based on exfoliated renal proximal tubule cells (RPTC) in urine. Subjects were divided into 3 salt sensitivity index categories: High-Salt-Sensitive (HSS; ≥ 7 mmHg increase in mean arterial pressure (MAP) on a high salt diet of 300 mEq of sodium, 17%prevalence), Low-Salt-Sensitive (LSS; ≥ 7 mmHg increase in MAP on a low salt diet of 10 mEq of sodium, 11% prevalence) and Salt Resistant (SR; ≤ 7 mmHg increase in MAP on both high and low salt diets, 72% prevalence) (Carey et al., in review). Three individuals were analyzed in each category on a minimum of 3 separate occasions. Cells were isolated from urine using centrifugation and measured for dopamine-1 receptor (D1R) plasma membrane recruitment using fluorescently-labeled antibodies under a confocal microscope as well as in a flow cytometer. Confocal microscopy analysis (total of 100 RPTCs for the 9 subjects) showed a negative correlation between salt-sensitivity index and D1R surface recruitment in RPTCs in their response to salt stimulation (y = -0.0073x + 0.5248, p = 0.0159). Flow cytometry analysis (total of 4938 RPTCs for the 9 subjects) also demonstrated a negative correlation between salt-induced D1R recruitment and salt-sensitivity (y = -2.547x + 239.97, p < 0.0001). Flow cytometry analysis showed a greater degree of separation amongst the subjects than confocal microscopy analysis, and would allow for a rapid diagnostic use of exfoliated renal cells in urine. Cryopreserved RPTCs (viability = 57.16% ± 9.15%, n = 12) compare favorably with cell viability from freshly voided urine cells and were still capable of eliciting intracellular sodium-mediated D1R recruitment. Cryopreservation thus enables batch collection, transport and processing of specimens between sites. We expect these procedures to provide a novel and convenient method of diagnosing the salt-sensitivity index in humans.
- © 2012 by American Heart Association, Inc.