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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

www.cvja.co.za

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,

alta.schutte@nwu.ac.za

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