Glomerular hyperfiltration during sympathetic nervous system activation in early essential hypertension.

Abstract

Glomerular hyperfiltration may be important for the development of essential hypertension. Both the renin-angiotensin system and the sympathetic nervous system influence renal hemodynamic regulation. To test the hypothesis that glomerular hyperfiltration can be unmasked by sympathetic nervous system activation, renal hemodynamics and humoral components of the renin-angiotensin system were examined at rest and during mental stress in 45 young normotensive healthy subjects and 37 young people with mild essential hypertension. GFR and renal plasma flow (RPF) were determined with inulin and para-aminohippuric acid clearance at rest and during stress. At rest, RPF, GFR, filtration fraction, plasma renin activity, angiotensin (Ang) II concentrations, and serum aldosterone values were similar in normotensive and hypertensive subjects. After stress, blood pressure increased (P < 0.01), but this was nearly identical in normotensive and hypertensive subjects (7.05 +/- 6.9 versus 7.03 +/- 4.6 mmHg, NS). The decrease in RPF (-27 +/- 54 versus -22 +/- 25 ml/min per 1.73 m2, NS) was also similar in the two groups. In contrast, the increase in GFR (+ 10.5 +/- 7.2 versus 6.08 +/- 5.7 ml/min per 1.73 m2, P < 0.001) and filtration fraction (+2.48 +/- 1.38 versus 1.82 +/- 1.49%, P < 0.05) was more marked in hypertensive than in normotensive subjects. The concomitant increase in Ang II concentrations was greater in hypertensive than in normotensive subjects (+4.6 +/- 1.0 versus -1.0 +/- 0.45 pg/ml, P < 0.001). The increase in GFR during mental stress was correlated with the increment in Ang II concentrations (r = 0.39, P < 0.001). Compared with the placebo control phase, blockade of the renin-angiotensin system with an angiotensin-converting enzyme inhibitor attenuated the increase in GFR during stress in hypertensive (8.04 +/- 5.01 versus 10.1 +/- 5.7 ml/min per 1.73 m2, P < 0.05), but not in normotensive, subjects. Even in early essential hypertension, glomerular hyperfiltration is evident during sympathetic nervous system activation, which is mediated by postglomerular vasoconstriction. This early stress-induced glomerular hyperfiltration may contribute to, or trigger, the development of essential hypertension.