CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 2, March 2012
82
AFRICA
increased vascular reactivity in the hypertensive African women
corresponds to previous studies that found an increased relative
risk for hypertension in both Africans and African-Americans
compared to other ethnic groups, due to increased measure-
ments of cardiovascular reactivity when a specific stressor was
applied.
2,3,5,19-23
CRP was significantly correlated with WC and BMI in the
hypertensive African women. However, this observation did not
apply to the Caucasian women (Table 3). These observations
agree with previous studies, where it was shown that CRP had
its strongest correlations with BMI and WC,
7,24-26
and that these
correlations were most noticeable among African-American and
African women.
7,27
Mean values of BMI and WC in hypertensive African women
also significantly increased (Table 2). This increase in mean
body fat indicators could possibly explain the high correlations
with CRP when one considers the relationship between IL-6 and
CRP concentrations. IL-6 is expressed in adipose tissue and this
inflammatory marker in turn stimulates the production of CRP
in the liver.
24,28
In addition, IL-6 has been shown to increase with
increasing adiposity in healthy men and women, with higher
amounts being expressed in visceral fat depots compared to
subcutaneous fat depots.
12,13,29
This mechanism could possibly
explain the observed higher correlation with WC compared to
BMI in African women, as BMI represents overall adiposity
whereas WC represents abdominal adiposity.
This could possibly be attributed to the observation that
the normotensive Caucasian and African women had already
exhibited elevated mean values of both BMI and WC (Table
2) before reaching hypertensive status. These individuals could
already have been exhibiting reactivity of the HPA axis
9-11,29-32
to
the elevated adiposity, and therefore a significant correlation to
both CRP and cortisol was seen. Since the duration of obesity
was unknown, the loss of these correlations in the hypertensive
groups could possibly be attributed to dysregulation of the HPA
axis,
4,10,18
which was further supported by the observed hypocor-
tisolism (Table 2).
CRP was associated with all cardiovascular variables in the
hypertensive African women. However, the highest correlations
were exhibited with the peripheral vascular reactivity indica-
tors, TPR and Cw (Table 3). Once again, these observations, in
conjunction with the significant differences between the mean
values of these indices (Table 2), suggest a complementary
peripheral cardiovascular reactivity accompanying an increase in
blood pressure in African women.
This, together with the significant associations with CRP
in this group, is congruous with previous studies where CRP
was reported to be associated with hypertensive blood pres-
sure values, with greater associations occurring among women
and black ethnic groups.
28,29,33-42
In addition, increases in blood
pressure in obese African-American women have previously
been demonstrated, with a greater indexed peripheral resistance,
taking into account body surface area and not BMI (compared
to Caucasians).
21,43
Moreover, CRP levels have previously corre-
sponded to an increased likelihood of peripheral arterial disease
in United States adults, independent of smoking, WC, BMI,
hypertension and other confounders.
44
It can therefore be deduced that in African women, the high
correlations between CRP and the peripheral cardiovascular vari-
ables TPR and Cw suggest a greater risk for the development
of hypertension and consequently the development of cardio-
vascular disease. In addition to these observations, the overall
mean values of CRP were higher in Africans compared with
Caucasians (Table 1). However, both ethnic groups demonstrated
CRP levels that fell within the high-risk group for CVD (
>
3.0
mg/l).
45
Caucasian women displayed a significant correlation
between CRP and both SV (
r
=
0.84;
p
=
0.01) and Cw (
r
=
0.83;
p
=
0.01) (Table 3).
Previous studies have found that increased CRP levels have
been associated with decreased nitric oxide production.
37,45
Inhibition of nitric oxide in turn leads to increased
α
-adrenergic
effects, including increased vasoconstriction and sympathetic
activity.
46
We suggest that the inhibition of nitric oxide produc-
tion could possibly explain the decrease in Cw and the signifi-
cant increases in CO and SV values (Table 2), in conjunction
with the high correlations of CRP with SV and Cw (Table 3).
Therefore the increased CRP in Caucasian women could feasi-
bly cause endothelial dysfunction, which in turn could lead to
hypertension and subsequent cardiovascular dysfunction. Both
Caucasian and African women therefore exhibited possible risk
markers for future cardiovascular disease.
Cortisol correlated significantly with both Cw and TPR in
the hypertensive African women, whereas in the Caucasian
women there was a significant correlation with only Cw (Table
4). Decreased cortisol levels were also exhibited in both hyper-
tensive ethnic groups (Table 2). This could be indicative of hypo-
cortisolism, which has previously been displayed in hypertension,
particularly in African women.
4,10,18
Suggestions have been made
that this could be attributed to dysregulation of the HPA axis,
which in turn is mediated by certain inflammatory markers such
as CRP.
15
Therefore the high correlation between Cw and TPR in
these ethnic groups could still be attributed to the initial effects
of increased cortisol production by the HPA axis in response to
stress. This in turn could further support the significant increase
in the cardiac markers CO and SV in the hypertensive Caucasian
women (Table 2), and the significant increase in means of TPR
and Cw in the hypertensive African women (Table 2).
A possible mechanism for this could be the permissive effect
of norepinephrine release by cortisol stimulation and subsequent
b
-adrenergic responses.
46
In the hypertensive African women,
SBP and the vascular marker Cw predicted hypertension (Table
5), suggesting possible dysregulation of the HPA axis in conjunc-
tion with norepinephrine release by cortisol stimulation in this
group.
4,10,15,18,46
Therefore in the hypertensive African women,
dysregulation of the HPA axis is the most likely explanation.
However, in the hypertensive Caucasian women, these observa-
tions were not reiterated.
A limitation of this study could be the duration of obesity in
the participants, which could have influenced the habituation/
adaptation of physiological resources. Furthermore, one needs
to consider that hs-CRP is a non-specific marker for inflamma-
tion and although the participants in this study were apparently
healthy, the higher hs-CRP levels could possibly be explained by
other unknown inflammatory conditions.
45
Additionally, the time
difference in data collection could have influenced the results,
although temperatures were similar for both collection periods
(autumn and spring). The significance of this study could have
been further substantiated if more data were obtained regard-
ing duration of stay in an urban area. Additionally, the use of
hormone replacement therapy or oral contraceptives should have
