CARDIOVASCULAR JOURNAL OF AFRICA • Vol 23, No 7, August 2012
AFRICA
397
Endothelin-1 was measured using an
125
I immuno-assay
radioactive ligand system (Amersham Biosciences International,
South Africa, Cat no RPA 555). Briefly, the assay is based on
the competition between unlabelled ET-1 and a fixed quantity of
125
I-labelled ET-3 (synthetic) for a limited number of binding sites
on an ET-1-specific antibody. With fixed amounts of antibody
and radioactive ligand, the amount of radioactive ligand bound
by the antibody is inversely proportional to the concentration of
the added non-radioactive ligand.
Theantibody-boundET-1 is then reactedwitha secondantibody
that is bound to magnetisable polymer particles. Separation of
the antibody-bound fraction is effected by centrifugation of the
suspension and decantation of the supernatant. Measurement of
the radioactivity in the pellet enables the amount of labelled ET-3
in the bound fraction to be calculated. The concentration of the
unlabelled ET-1 in the sample was determined from a standard
curve. All samples were done in triplicate.
Venous blood (5 ml) was collected into heparinised tubes and
centrifuged immediately at 2 000 ×
g
for 10 minutes at 4°C to
remove the cells, after which the plasma was stored at –70°C
for later analysis. Samples were then prepared and analysed
according to the manufacturer’s instructions.
Blood was also collected for routine blood analysis, including
renin, aldosterone, cholesterol, glucose and electrolyte levels,
and liver function. In the hypertensive patients all measurements
were done and blood samples collected at baseline (before
therapy), and after one, three, six and nine months of therapy.
Statistical analysis
Analysis of variance (applying the Bonferroni principle) was
used to determine intra-group variations at the different intervals.
Comparisons between the control (healthy volunteers) and
the experimental group (treatment-naïve patients) were done
using the Mann-Whitney rank sum test. A
p
-value of
<
0.05
was considered significant. Pearson’s coefficient was used
to determine correlations between PWV, ET-1 levels and the
other parameters. Descriptive statistics were given as median
(1st quartile–3rd quartile).
The study was approved by the Medunsa Research Ethics
Committee of the University of Limpopo, IRB 00005122.
Results
Of the 44 newly diagnosed hypertensive patients, 14 were male
and 30 female, aged 50.4
±
7.6 years, whereas in the control
group, 19 were male and 32 female, aged 43.2
±
8.3 years. The
BMI at the beginning of the study period was 28
±
6.9 kg/m
2
for the control group and 31.5
±
6.9 kg/m
2
for the patient group.
Five patients were regarded as lost to follow up, of whom
three did not respond to perindopril alone and were give
2.5 mg indapamide, and three patients developed a dry cough.
Thirty-nine patients completed the nine-month period on 4 mg
perindopril.
There was a significant decrease in systolic, diastolic and
mean arterial pressure in the treatment group at each visit
compared to baseline, but pulse pressure did not change. Values
never reached the same level as those of the control group
(Table 1).
There was a significant continuous reduction in PWV that
could indicate an increase in arterial elasticity in the carotid–
femoral segment of the treatment group, from a median of 11.6
to 7.5 m/s over the nine-month period. The PWV of the treatment
group (median 7.5 m/s) after nine months was lower than that
of the healthy volunteer group (median 8.2 m/s) but was not
statistically significant (Table 2).
Although the absolute values of the PWV in the brachial–
ulnar segment of the treatment group decreased over time, it was
not significant. After the nine-month treatment, the average value
was lower than that of the healthy volunteer group. The median
PWV in the brachial–ulnar segment at all treatment intervals was
lower than that of the carotid–femoral segment (Table 2).
All values are given as median (1st–3rd quartile). ET-1 levels
in the treatment group first increased from 6.15 (3.5–7.89)
pmol/l at baseline to reach a maximum of 8.15 (5.32–9.63)
pmol/l after six months but it was not significant. They then
decreased to 4.53 (3.68–9.2) pmol/l after nine months.
The ET-1 levels of the treatment group after nine months
were lower than those of the healthy volunteer group but it was
not significant. The baseline level of ET-1 in the treatment group
was significantly higher [6.15 (3.5–7.89) pmol/l] than that of the
healthy volunteer group [4.69 (3.0–5.4) pmol/l] (Table 2).
Neither BMI nor other routine blood tests changed during the
nine-month study period.
Discussion
In this study we investigated the effect of a nine-month treatment
with the ACE inhibitor perindopril on PWV and the role of ET-1
in black hypertensive patients. PWV was used as a surrogate to
TABLE 1. EFFECT OF PERINDOPRIL 4 MG DAILY ON BLOOD PRESSURE IN BLACK HYPERTENSIVE
PATIENTSAFTERA NINE-MONTHTREATMENT COMPARED TO HEALTHYVOLUNTEERS
Patients (
n
=
39)
Variable median (IQF 1–3)
Control (
n
=
51)
M0
M1
M3
M6
M9
SBP (mmHg)
116**
(109–127)
149
(140–154)
145*
(135–150)
137*
(130–150)
134*
(130–146)
136*
(127–149)
DBP (mmHg)
73**
(65–80)
90
(85–96)
90
(85–100)
85
(80–93)
83*
(77–90)
81*
(75–87)
MAP (mmHg)
88
(79–96)
110
(106–113)
105
(92–113)
99.4
(88–108.2)
96.6*
(85.91–105.4)
97.6*
(83.9–104.6)
PP (mmHg)
47
(39–53)
55
(50–63)
55
(45–60)
50
(43–55)
50
(47–60)
56
(49–63)
Values are median IQF 25–75% (1st–3rd). SBP: systolic blood pressure, DBP: diastolic blood pressure, MAP: mean arterial pressure, PP: pulse pressure.
*Compared to baseline M0, (M1, M3, M6, M9) after one, three, six and nine months of therapy (
p
<
0.05 Mann-Whitney rank sum test).
**Comparison between healthy volunteers (control) and baseline (M0) of patients before treatment. (
p
<
0.05 Mann-Whitney rank sum test).
