RENAL HEMODYNAMICS AND CARDIOVASCULAR REACTIVITY IN THE PREHYPERTENSIVE STAGE

To examine whether sympathetic nervous activation has an impact on ren al circulation in subjects at risk for high blood pressure, we assesse d renal hemodynamics and cardiovascular response to mental stress in 4 0 healthy young white males, 12 normotensive subjects without and 14 w ith familial hypertension, and 14 with borderline hypertension. The re sponse of systolic and diastolic blood pressure to mental stress was a ssessed while each patient performed a mental arithmetic task, this wa s taken as the parameter for the activation of the sympathetic nervous system. Renal plasma flow was measured by para-aminohippuric acid cle arance under steady-state conditions. In parallel, glomerular filtrati on rate as a parameter for functional impairment of the kidneys was de termined by creatinine clearance, and filtration fraction was also cal culated. Patients with borderline hypertension were characterized by a reduced renal blood flow and increased filtration fraction in compari son with both normotensive groups. The increase in systolic blood pres sure during mental stress was more pronounced in borderline hypertensi ves. We observed no significant difference in renal hemodynamics and c ardiovascular response to mental stress between normotensives with and without a family history of hypertension. In the total population, ca rdiovascular response to mental stress was correlated with renal hemod ynamics. The greater the increase in systolic blood pressure during me ntal stress, the lower was the renal plasma flow and the greater the f iltration fraction. Thus, renal plasma flow was found to be already re duced and filtration fraction increased before sustained hypertension developed. Because this pattern in renal hemodynamics was related to c ardiovascular response to mental stress, our data suggest that sympath etic activation already appeared to affect renal hemodynamics at the o nset of essential hypertension.