Aldosterone
Aldosterone is a steroid hormone secreted by adrenal glands. Its main role is to regulate salt and water in the body, thus having an effect on blood pressure.
What is Aldosterone?
Aldosterone is a steroid hormone produced in the outer section (cortex) of the adrenal glands, which sit above the kidneys.
It plays a central role in the regulation of blood pressure mainly by acting on organs such as the kidney and the colon to increase the amount of salt (sodium) reabsorbed into the bloodstream and to increase the amount of potassium excreted in the urine.
Aldosterone also causes water to be reabsorbed along with sodium; this increases blood volume and therefore blood pressure.
Functions of Aldosterone
Aldosterone is the primary of several endogenous members of the class of mineralocorticoids in human.
Deoxycorticosterone is another important member of this class.
At the late distal tubule & collecting duct, aldosterone has two main actions:
Acting on mineralocorticoid receptors (MR) on principal cells in the distal tubule of the kidney nephron, it increases the permeability of their apical (luminal) membrane to potassium and sodium and activates their basolateral Na+/K+ pumps, stimulating ATP hydrolysis leading to phosphorylation of the pump and a conformational change in the pump exposes the Na+ ions to the outside.
Aldosterone stimulates H+ secretion by intercalated cells in the collecting duct, regulating plasma bicarbonate (HCO3−) levels and its acid/base balance.
Aldosterone may act on the central nervous system via the posterior pituitary gland to release vasopressin (ADH) which serves to conserve water by direct actions on renal tubular resorption.
How is Aldosterone controlled?
Aldosterone is part of a group of linked hormones, which form the renin–angiotensin–aldosterone system.
Activation of this system occurs when there is decrease in blood flow to the kidneys following loss of blood volume or a drop in blood pressure (e.g. due to a haemorrhage).
Renin is an enzyme that leads to a series of chemical reactions resulting in the production of angiotensin II, which in turn stimulate aldosterone release.
Aldosterone causes an increase in salt and water reabsorption into the bloodstream from the kidney thereby increasing the blood volume, restoring salt levels and blood pressure.
What happens if I have too much Aldosterone?
The most common cause of high aldosterone levels is excess production, frequently from a small benign adrenal tumour (primary hyperaldosteronism).
The symptoms include high blood pressure, low blood levels of potassium and an abnormal increase in blood volume.
What happens if I have too little Aldosterone?
Low aldosterone levels are found in a rare condition called Addison’s disease.
In Addison’s disease, there is a general loss of adrenal function resulting in low blood pressure, lethargy and an increase in potassium levels in the blood (see the article on Addison’s disease for further information).