Determinants of Arterial Blood Pressure in Urban Ghanaians: Plasma Renin Activity and Sodium Balance

Abstract

In the tropics, prevailing weather conditions exert a tremendous influence on fluid and electrolyte homeostasis of residents. For the tropical resident, who may have evolved an adaptive strategy to conserve sodium and water by renal and hormonal mechanisms, increases in sodium intake may cause changes that would, in the long term, lead to an increase in the arterial blood pressure. In this study, three serial protocols were followed to elucidate the significant role of sodium balance and the regulatory renin-angiotensin system in determining the arterial blood pressure of urban resident Ghanaians, and as a basis to explain the recent observed increase in the prevalence of hypertension in Ghana. The first series of the investigation showed a rising trend in the arterial blood pressure with advancing age for 31 randomly selected subjects; a phenomenon associated with populations on a high salt diet. In the second series, low levels of plasma renin activity (mean = 0.71 ± 0.13 pmol Ang. I/ml/hr) were obtained in 10 subjects (8 normotensive and 2 hypertensive). Such low levels of plasma renin activity, signifying a suppressed renin-angiotensin system, is also associated with a high salt intake. Finally, the last series on 11 subjects, who were fed ad lib, revealed a high intake of sodium (mean = 295.2 ± 9.0 mmol) at a threshold of 300 mmol above which the subjects could not effectively excrete any extra sodium load. The significance of such findings, albeit using different subject groups and a small sample population, is that sodium homeostasis can be considered as a major determinant of arterial blood pressure of tropical residents. Given the present recognition of sodium (salt) as an environmental stressor, and considering its ready availability, accessibility and affordability, high intakes, as observed in this study, could lead to elevation of the blood pressure. This may set the stage for explaining the recent observations regarding the increase in prevalence of hypertension in Ghana.