The association of the change in renin with cardiovascular and inflammatory markers in a bi-ethnic population : the SABPA study

Abstract

Motivation : A study done in South Africa stated that black participants have lower renin levels in comparison to white participants, which may be linked to the increased prevalence of cardiovascular disease (CVD) in this population. In relation to the lower renin levels, angiotensin II (Ang II) levels may also be suppressed in this population. It was also indicated that black South Africans are prone to chronic low grade inflammation. If the renin angiotensin-system (RAS) is activated it may lead to increased inflammation due to the actions of Ang II which may indirectly increase C-reactive protein (CRP) levels. The RAS is suppressed in the black participants, thus they may have lower Ang II levels, but increased levels of inflammation and high risk of CVD. Therefore, an investigation into these mechanisms may give insight into the interaction between the RAS, inflammation and cardiovascular variables. Aim : The aim of the study was to investigate associations of change in renin with cardiovascular and inflammatory markers in a low renin black and white population. Methods : This study formed part of the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) prospective cohort study that took place between 2008 and 2011. The study population consisted of 73 black and 81 white teachers between 20-65 years of age, from the Dr. Kenneth Kaunda Education District in the North-West Province of South Africa. The anthropometric variables included height and weight. Regarding cardiovascular measurements systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), total peripheral resistance (TPR), Windkessel compliance (Cwk) and carotid intima media thickness (cIMT) were determined. Biochemical variables included renin, CRP, interleukin-6 (IL-6), glucose, von Willebrand factor (vWf), triglycerides and cholesterol levels. Means and proportions were compared using independent t-tests and Chi-square tests, respectively. Variables were compared using analyses of covariance (ANCOVA). Correlations of variables were performed using partial regression analyses. Forward stepwise multiple regression analyses were performed to determine independent associations between variables. Results and conclusion : Percentage change in renin levels was independently and inversely associated with percentage change in systolic blood pressure (β=-0.27; p=0.011) only in black participants with low renin. Among the white participants percentage change in renin was negatively associated with percentage change in IL-6 (β=-0.24; p=0.005). In conclusion, in black participants with low renin levels at baseline, a further decrease in renin levels over three years is independently associated with an increase in SBP. These results strengthen the notion that low renin may be a causative factor in the development of hypertension in black South Africans, but that the renin- angiotensin system is not the driving force behind the increased inflammation observed in this low renin black group.