Aldosterone and renin in relation to surrogate measures of sympathetic activity: the SABPA study.

INTRODUCTION: Hypertension, particularly in black populations, is often accompanied by augmented sympathetic nervous system activity and suppressed renin activity, indicative of possible blood pressure (BP) dysregulation. The potential role of the interrelationship between the renin-angiotensin-aldosterone system (RAAS) and the sympathetic nervous system in the context of low-renin conditions is unclear. We therefore explored whether surrogate measures of sympathetic activity [noradrenaline, 24-hour heart rate (HR) and percentage (%) dipping of night-time HR] relate to renin, aldosterone and aldosterone-to-renin ratio (ARR) in black and white South Africans.

METHODS: We included black (n = 127) and white (n = 179) males and females aged 20-63 years. We measured 24-hour BP and HR, and calculated night-time dipping. We determined renin and aldosterone levels in plasma and calculated ARR. Noradrenaline and creatinine levels were determined in urine and the noradrenaline:creatinine ratio was calculated.

RESULTS: More blacks had low renin levels (80.3%) compared to whites (58.7%) (p < 0.001). In univariate and after multivariate analyses the following significant associations were evident in only the black group: HR dipping was associated negatively with aldosterone level (β = -0.18, p = 0.024) and ARR (β = -0.20, p = 0.011), while 24-hour HR was associated positively with renin level (β = 0.20, p = 0.024). Additionally, there was a borderline significant positive association between noradrenaline:creatinine ratio and aldosterone level (β = 0.19, p = 0.051).

CONCLUSIONS: The observed associations between surrogate measures of sympathetic nervous system activity and components of the RAAS in the black group suggest that the adverse effects of aldosterone and its ratio to renin on the cardiovascular system may be coupled to the effects of the sympathetic nervous system.