| Summary: | Motivation: Abdominal obesity (hereafter referred to as "obesity") is
becoming the biggest "global epidemic" of our modern times. It is associated
with a range of diseases, including cardiovascular diseases and hypertension.
Recent research showed that an increase in sympathetic activity is of central
importance in the pathogenesis of obesity-related diseases. Increased leptin
levels and impaired baroreflex sensitivity have both been independently
associated with abdominal obesity and increased sympathetic activity. A
perception of poorer health may also contribute to the physiological
characteristics of obesity-related diseases. A lack of data regarding
sympathetic activity, leptin levels, baroreflex sensitivity and perception of
health in Africans, serves as a motivation for conducting this study.
Objective: To investigate the contributions of leptin levels, baroreflex
sensitivity and perception of health data to increased sympathetic activity in
lean and obese African women from South Africa.
Methodology: The manuscript presented in Chapter 2 made use of the data
obtained in the POWIRS (Profiles of Obese Women with the Insulin
Resistance Syndrome) study. A group of 102 urbanized African women, living
in the North-West Province of South Africa, was recruited according to body
mass indexes. Only 85 subjects were included for analysis due to incomplete datasets. For this study, subjects were divided into lean and obese groups
according to their waist circumferences. Anthropometric measurements were
done according to standardized methods. Resting cardiovascular
measurements were obtained from Finometer observations. Resting, fasting
levels of leptin were calculated after radioimmunoassay analyses. Subjective
perception of health was determined by means of the 28-item General Health
Questionnaire. Comparisons between the groups were done using analysis of
covariance (ANCOVA) whilst adjusting for cardiovascular risk factors (age.
smoking, alcohol consumption and physical activity). Correlation coefficients
were determined to indicate any associations between leptin, baroreflex
sensitivity and perception of health with sympathetic activity (represented by
heart rate) and other cardiovascular variables.
The study was approved by the Ethics committee of the North-West University
and all the subjects gave informed consent in writing. The reader is referred to
the Methods section in Chapter 2 for a more detailed description of the
subjects, study design and analytical procedures used in this dissertation.
Results and conclusion: Results from this study indicate that obese African
women, compared to lean African women, were older, reported higher
physical activity, and exhibited higher diastolic and mean blood pressure,
heart rate, cardiac output, arterial compliance, leptin and hypertension
prevalence rate values. In lean African women social dysfunction was
positively associated with diastolic and mean blood pressure and arterial
resistance, and negatively with arterial compliance. In obese African women baroreflex sensitivity was negatively associated with diastolic blood pressure,
which could be an indication of impaired baroreflex sensitivity. In this obese
group a perception of social dysfunction was associated with decreased heart
rate. Although leptin and heart rate were significantly higher in the obese
Africans, no significant correlations existed between these variables to reflect
leptin's enhancement of sympathetic activity. However, leptin correlated
weakly but positively with cardiac output (p = 0.054, r = 0.32). In conclusion,
baroreflex sensitivity (although similar between groups) and leptin seem to
contribute to blood pressure and thus hypertension in obese African women,
possibly through increased sympathetic activity and volume loading. A
perception of poorer health, especially a perception of social dysfunction,
could possibly contribute to this image. === Thesis (M.Sc. (Physiology))--North-West University, Potchefstroom Campus, 2007.
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