Renal Hemodynamics and Cardiovascular Reactivity in the Prehypertensive Stage

To examine whether sympathetic nervous activation has an impact on renal circulation in subjects at risk for high blood pressure, we assessed renal hemodynamics and cardiovascular response to mental stress in 40 healthy young white males, 12 normotensive subjects without and 14 with familial hypertension, and 14 with borderline hypertension. The response of systolic and diastolic blood pressure to mental stress was assessed while each patient performed a mental arithmetic task; this was taken as the parameter for the activation of the sympathetic nervous system. Renal plasma flow was measured by para-aminohippuric acid clearance under steady-state conditions. In parallel, glomerular filtration rate as a parameter for functional impairment of the kidneys was determined by creatinine clearance, and filtration fraction was also calculated. Patients with borderline hypertension were characterized by a reduced renal blood flow and increased filtration fraction in comparison with both normotensive groups. The increase in systolic blood pressure during mental stress was more pronounced in borderline hypertensives. We observed no significant difference in renal hemodynamics and cardiovascular response to mental stress between normotensives with and without a family history of hypertension. In the total population, cardiovascular response to mental stress was correlated with renal hemodynamics: The greater the increase in systolic blood pressure during mental stress, the lower was the renal plasma flow and the greater the filtration fraction. Thus, renal plasma flow was found to be already reduced and filtration fraction increased before sustained hypertension developed. Because this pattern in renal hemodynamics was related to cardiovascular response to mental stress, our data suggest that sympathetic activation already appeared to affect renal hemodynamics at the onset of essential hypertension.