Aldosterone
Overview
Aldosterone is a hormone produced by the adrenal glands in the human body. It is part of the renin-angiotensin-aldosterone system (RAAS) and plays a crucial role in the regulation of blood pressure and electrolyte balance.
Biochemistry
Aldosterone is a steroid hormone, specifically a mineralocorticoid. It is synthesized in the zona glomerulosa of the adrenal cortex. The synthesis of aldosterone involves a series of enzymatic reactions, starting with the conversion of cholesterol to pregnenolone by the enzyme cholesterol side-chain cleavage enzyme (P450scc). Pregnenolone is then converted to progesterone, which is further converted to deoxycorticosterone (DOC). Finally, DOC is converted to aldosterone by the enzymes aldosterone synthase (CYP11B2) and 3β-hydroxysteroid dehydrogenase (3β-HSD).
Function
Aldosterone acts on the cells of the distal convoluted tubules and collecting ducts in the kidneys. It increases the reabsorption of sodium ions (Na+) and the excretion of potassium ions (K+) and hydrogen ions (H+). This action alters the osmotic balance, leading to the retention of water in the body, which in turn increases blood volume and blood pressure.
Regulation
The production and release of aldosterone are primarily regulated by the renin-angiotensin-aldosterone system (RAAS). When blood pressure drops, the juxtaglomerular apparatus in the kidneys releases renin, which converts angiotensinogen to angiotensin I. Angiotensin I is then converted to angiotensin II by the enzyme angiotensin-converting enzyme (ACE). Angiotensin II stimulates the adrenal glands to produce and release aldosterone.
Clinical significance
Abnormal levels of aldosterone can lead to several medical conditions. Excessive production of aldosterone, known as hyperaldosteronism, can cause high blood pressure and low potassium levels. On the other hand, insufficient production of aldosterone, known as hypoaldosteronism, can result in low sodium levels, high potassium levels, and acidosis. These conditions can be diagnosed through blood tests and urine tests and are typically treated with medications that regulate aldosterone levels.