Cardiovascular Journal of Africa: Vol 30 No 1 (January/February 2019)

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CARDIOVASCULAR JOURNAL OF AFRICA • Volume 30, No 1, January/February 2019 34 AFRICA
Aldosterone and renin in relation to surrogate measures
of sympathetic activity: the SABPA study
Lebo F Gafane-Matemane, Johannes M van Rooyen, Rudolph Schutte, Aletta E Schutte
Abstract
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–aldos-
terone 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 multi-
variate 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).
Conclusion: The observed associations between surrogate
measures of sympathetic nervous system activity and compo-
nents 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.
Keywords: heart rate, blood pressure, dipping, renin–angioten-
sin–aldosterone system, noradrenaline
Submitted 6/12/17, accepted 31/10/18
Published online 22/1/19
Cardiovasc J Afr 2019; 30: 34–40
DOI: 10.5830/CVJA-2018-065
Hypertension is the most common risk factor for cardiovascular
events and its prevalence continues to increase in sub-Saharan
Africa.1,2 A suppressed renin–angiotensin–aldosterone
system (RAAS) and increased nocturnal blood pressure (BP)
(non-dipping) are among the prominent features of hypertension
in black populations.3-6 Low-renin hypertension may reflect a
physiological response to increased BP and sodium/volume
overload attributable to aldosterone.7
Even modest increases in aldosterone levels, as indicated
by a high aldosterone-to-renin ratio (ARR),8,9 particularly in
the presence of high sodium intake, result in high BP in black
populations.10,11 In salt-sensitive blacks on sodium loading,
blockade of angiotensin II receptors increased renin activity and
reduced plasma aldosterone level, resulting in reduced night-time
BP.12 It is therefore probable that sympathetic drive and blunted
decrease in aldosterone level may be the driving force for increases
in night-time BP. The detrimental effects of aldosterone in black
populations may be augmented by increased mineralocorticoid
receptor sensitivity, 4,13 rather than increased aldosterone levels
resulting from stimulation of the RAAS.
Aldosterone also influences the autonomic nervous system by,
for example, blunting the baroreflex response and potentiating
the vasoconstrictor effects of noradrenaline.14,15 Blockade of
aldosterone improves 24-hour heart rate (HR) variability and
reduces HR, particularly in the early morning hours when
sympathetic nervous system activity is high.16 Additionally, HR
is associated with muscle sympathetic nervous system activity,
which is the gold standard for assessing sympathetic nervous
system outflow and plasma noradrenaline levels,17 while reduced
HR dipping or a higher night-time HR can also represent a state
of sympathetic nervous system overdrive.18
However, it is not clear if the interplay of aldosterone and
its ratio to renin (ARR) with the sympathetic nervous system is
evident in black populations who are predisposed to low-renin
hypertension. To address this, we determined whether surrogate
measures of sympathetic activity [noradrenaline, 24-hour HR
and percentage (%) dipping in HR] related to renin and
aldosterone levels, and ARR in black and white South Africans.
Methods
The Sympathetic activity and Ambulatory Blood Pressure in
Africans (SABPA) study was conducted between February 2008
Hypertension in Africa Research Team (HART), North-West
University, Potchefstroom, South Africa
Lebo F Gafane-Matemane, PhD
Johannes M van Rooyen, DSc
Rudolph Schutte, PhD
Aletta E Schutte, PhD,
Department of Medicine and Healthcare Science, Faculty
of Medical Science, Anglia Ruskin University, Chelmsford,
United Kingdom
Rudolph Schutte, PhD
Research Unit for Hypertension and Cardiovascular
Disease, Medical Research Council, North-West University,
Potchefstroom, South Africa
Lebo F Gafane-Matemane, PhD
Johannes M van Rooyen, DSc
Aletta E Schutte, PhD