|dc.description.abstract||Motivation: The prevalence of obesity is the highest among African women in South Africa.
Since obesity is a major cardiovascular risk factor, African women in South Africa could be
regarded as a high risk group. However, investigations on obesity-related hypertension are
limited in this population group. The associations of body fat distribution and hormones such as
leptin and endothelin-1 with cardiovascular function have not yet been determined in these
women. It has been determined that endothelin-1 is a role player in the development and/or
maintenance of hypertension in various population groups, especially African Americans.
Endothelin-1 has also been found to be involved in obesity-related hypertension in non-African
population groups. It has been indicated that the obesity-related hormone, leptin, also plays a
role in obesity-related hypertension, especially in African Americans. Leptin levels have been
found to be higher in obese hypertensive African American women compared to an obese
normotensive control group. Since the above-mentioned two hormones playa prominent role in
obesity and hypertension in African American and non-African population groups, the lack of
data on African women in South Africa serves as motivation to conduct this investigation.
Aim: To investigate obesity-related hypertension in African women through the determination of
associations between various anthropometric and endocrinological variables with
cardiovascular, especially vascular function.
Methodology: Manuscripts presented in Chapters 2, 3 and 4 made use of data from the
POWIRS (Profiles of Obese Women suffering from the Insulin Resistance Syndrome) I project
where African women were selected from a government institution in the North West Province.
A group of 98 women were divided into lean normotensive, overweight/obese normotensive and
overweight/obese hypertensive groups. Anthropometric and cardiovascular measurements were
taken and the lipid profile, leptin and endothelin-1 levels determined. The analysis of covariance
(ANCOVA) was used to show significant differences between groups while adjusting for age.
Partial correlation coefficients were used to show associations between various variables while
adjusting for age. Stepwise linear regression analysis was also used to show associations
between variables. The study presented in Chapter 5 made use of both POWIRS I and II, which
are studies including Africans and Caucasians, respectively. The methodology of the two
studies was the same.
All subjects gave informed consent in writing and the Ethics Committee of the North-West
University approved the study. The reader is referred to the "Materials and Methods" section of
Chapters 2-5 for a more elaborate description of the subjects, study design and analytical
methods used in each article.
Results and conclusions of the individual manuscripts
> Results from Chapter 2 showed that the volume loading effect associated with obesity was
present in both overweight/obese normotensive and overweight/obese hypertensive
groups, however, the accommodating effect observed in the overweight/obese
normotensive group was absent in the overweight/obese hypertensive group due to
decreased vascular function. This was confirmed by a high pulse pressure. Decreased
vascular functioning was associated with the abdominal skin fold. This suggests that
abdominal subcutaneous fat may either be a marker of visceral fat, or may in itself
contribute to increased cardiovascular risk in Africans.
> Results from Chapter 3 showed a negative result. Plasma endothelin-1 levels were similar
for the lean normotensive, overweight/obese normotensive and overweight/obese
hypertensive groups. After re-dividing the groups into normotensive and hypertensive, and
then into lean and overweight/obese, still no differences could be obtained. Additionally,
no correlations could be obtained between endothelin-1 and cardiovascular function in any
of the groups. These findings suggest that endothelin-1 is not implicated in obesity-related
hypertension in African women.
> In Chapter 4, leptin levels were elevated in both overweight/obese normotensive and
hypertensive groups compared to the lean normotensive group. However, leptin levels did
not differ between the two overweight/obese groups. Even though leptin levels were the
same, leptin was directly and positively associated with systolic blood pressure and pulse
pressure and negatively with arterial compliance only in the overweight/obese
hypertensive group, independent of obesity, insulin resistance, hyperinsulinemia and age.
> In Chapter 5 the volume loading, as well as the accommodating effect, that is, decreased
total peripheral resistance and increased arterial compliance, was present in both African
and Caucasian obese groups compared to their lean controls. Even though leptin levels,
body mass index and age were similar for both African and Caucasian obese groups, the
accommodating effect seemed to be more prominent in the obese Caucasian group,
explaining a lower diastolic blood pressure compared to the obese African group. Leptin
showed a favourable negative association with diastolic blood pressure and total
peripheral resistance in the obese Caucasian group, but not in the obese African group.
This may indicate that leptin predominantly exerts pathological influences on obese
African women, as determined previously in Chapter 4.||