The widely-believed concept that high blood pressure is the result of excess salt causing an increased blood volume, exerting extra pressure on the arteries has been debunked by researchers.
Their research found that excess salt stimulates the sympathetic nervous system to produce adrenalin, causing artery constriction and hypertension.
The research was led by Irene Gavras, MD, and Haralambos Gavras, MD, both professors of medicine at Boston University School of Medicine.
The term "volume-expanded hypertension" implies that excess salt leads to the retention of extra fluid within the arterial circulatory system, causing an increase in blood volume and added pressure on the arterial walls.
However, research has shown that conditions characterized by the expansion of blood volume from other causes, such as the secretion of antidiuretic hormone or the excessive elevation of blood sugar, do not cause a rise in blood pressure because the extra fluid is accommodated by the distention of capillaries and veins.
"The body's circulatory system is a highly flexible vascular system with the capacity to open up new capillaries and distend veins in order to accommodate increased fluid volume," said Irene Gavras, MD, professor of medicine at BUSM.
Through a review of numerous studies, the researchers demonstrated that the mechanism of hypertension resulting from the excessive consumption and retention of salt stimulates the sympathetic nervous system in the brain to increase adrenaline production.
The increased adrenalin being circulated throughout the body causes the arteries to constrict, which results in resistance to blood flow and a decrease in circulatory volume.
The over-activation of the sympathetic nervous system - part of the autonomic nervous system that helps maintain the body's homeostasis - has been recognized clinically as a characteristic of hypertension that accompanies renal failure, which is the most typical example of elevated blood pressure from excessive salt retention.
Diuretics, which remove excess salt, are widely used to treat this type of hypertension.
However, this study provides convincing evidence that the sympathetic nervous system should be the focus of further investigations into treatments for hypertension.
"The implication of our findings shows that the optimal treatment for hypertension, for cases associated with renal failure, should not only include diuretics but also the use of drugs that block the central sympathetic nervous system," concluded Irene Gavras.
The study was published online in the Journal of Hypertension.