CARDIOVASCULAR/RENAL MECHANISMS OF HYPERTENSION

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The kidneys play a central role in long-term regulation of extracellular fluid volume and arterial pressure. Several lines of evidence also support an important role for the kidneys in the pathogenesis of hypertension. A common defect that has been found in all forms of hypertension examined to date is a hypertensive shift in the pressure natriuresis relationship. In the current proposal, a major objective is to examine the role of endothelin and nitric oxide in mediating the reduction in renal- pressure natriuresis in a specific form of hypertension associated with endothelial dysfunction--pregnancy-induced hypertension (PIH). Despite being the leading cause of maternal death and a major contributor of maternal and perinatal morbidity, the mechanisms responsible for the pathogenesis of PIH are unclear. Our current working hypothesis is that reduced uteroplacental perfusion causes hypertension by impairing renal- pressure natriuresis. Attenuated pressure natriuresis occurs as a result of placental factor(s) causing endothelial cell dysfunction leading to enhanced formation of vasoconstrictors (endothelin and thromboxane) and decreased formation of vasodilators (nitric oxide and prostacyclin). These endothelial abnormalities, in turn, reduce renal plasma flow and glomerular filtration rate or enhance tubular reabsorption, thereby decreasing renal sodium excretory function. To test this hypothesis, an integrated analysis of arterial pressure, renal, hormonal, and endothelial regulation will be conducted in a conscious, chronically-instrumented rat model of reduced uterine perfusion pressure (RUPP). Preliminary data in this model indicate that the hypertension produced by decreased perfusion pressure to the uteroplacental unit is associated with proteinuria, significant reductions in renal plasma flow and GFR, a hypertensive shift in the pressure natriuresis relationship, and endothelial dysfunction.