So is Aldosterone
Aldosterone is a steroid hormone produced by the adrenal glands with the aim of regulating the levels of sodium, potassium and the volume of extracellular fluids. More specifically, acting mainly in the kidney, aldosterone:
- increases sodium reabsorption in the distal tubule and collecting duct;
- increases the elimination of potassium and hydrogen ions.
Functions
Aldosterone is then secreted to rebalance the situation in conditions of hyperkalaemia (high concentration of potassium in the blood) or hyponatremia (reduced plasma sodium concentration), while its release will be inhibited in the opposite conditions.
Since sodium retention increases the volume of circulating blood and with it arterial pressure and fluid retention, hypovolemia, hypotension and vasoconstriction of the afferent renal arteriole also represent a positive stimulus for the secretion of aldosterone. This second control mechanism is mediated by the renin-angiotensin system: when the aforementioned conditions are captured in the glomerulus, some renal cells produce renin which, acting at the level of hepatic angiotensinogen, promotes the synthesis of Angiotensin I, in its once converted in the lungs and in the vascular endothelium to Angiotensin II. This powerful arteriolar vasoconstrictor will then stimulate the production of aldosterone in the adrenal glands, with consequent savings of water and sodium.
A third regulatory system is mediated by various hormones, including ACTH, catecholamines and atrial natriuretic peptide.
The actions of aldosterone extend somewhat to all the cells of the body, where it acts by facilitating the entry of sodium and promoting the loss of potassium (sweat glands, intestines and lacrimal glands). However, the main site of action remains the renal one: in the cytoplasm of the cells that make up the last third of the distal tubule and the portion of the collecting duct that runs in the cortical area of the kidney, there are specific receptors for aldosterone which, once linked to the hormone, they express proteins capable of increasing the reabsorption of sodium at the tubular level and at the same time favoring the secretion of potassium.
Hyperaldosteronism
This term refers to a condition characterized by an "excessive production of aldosterone. The most fearful consequence of this disease is" hypertension, since the kidney retains significant amounts of sodium with a consequent increase in circulating fluids (more blood → greater obstacle circulation → hypertension → cardiovascular damage).
Excessive aldosterone levels are also accompanied by hypokalaemia, resulting in increasing degrees of muscle weakness up to paralysis and heart pain.
Hyperaldosteronism can be caused by an adenoma or bilateral hyperplasia of the cortical zone of the adrenal gland. In the first case the surgical intervention can be decisive, while in the second one will proceed with the assumption of specific drugs (antialdosteronics).
Hyperaldosteronism can also be secondary to the intake of certain drugs (diuretics), to the stenosis of a renal artery and to other conditions of reninism (increased release of primary or secondary renin), to pregnancy or to an altered distribution of fluids in the extracellular compartment, such as in the presence of edema and in the course of liver cirrhosis or nephrotic syndrome. In all these cases there is a decrease in the volume which represents a stimulus for the renin-angiotensin system and the consequent production of aldosterone, whose plasma levels rise up to assume pathological connotations.
