| Aldosterone is a steroid hormone produced by the adrenal cortex, and is very important for keeping humans alive. Aldosterone is responsible for preserving salts in our body, keeping fluids in, and maintaining our blood pressure. Abnormally high levels of this hormone cause sodium retention, high blood pressure, heart rhythm irregularities and possibly paralysis. Aldosterone acts directly on the kidney to decrease the rate of sodium-ion excretion, and to increase the rate of potassium-ion excretion. Aldosterone helps
regulate the body's electrolyte balance by acting on the mineralocorticoid receptor (MR). Aldosterone diminishes the secretion of sodium (Na+) ions and therefore of water and stimulates the secretion of potassium (K+) ions through the kidneys. Aldosterone is the main sodium-retaining hormone from the adrenal gland. It increases the reabsorption of sodium and water along with the excretion of potassium in the distal tubules of the kidneys. This action raises blood pressure.
Aldosterone is formed in the outer-section (zona glomerulosa) of the adrenal cortex of the adrenal gland, as the cells of other sections don't have the corresponding enzyme. It is the sole endogenous member of the class of mineralocorticoids. Aldosterone is synthesized in reaction to increases of angiotensin II or plasma potassium, which are present in proportion to sodium deficiencies. It is also synthesized in response to different cytokines that get secreted due to hyperthermia. Aldosterone secretion is influenced by various signals involving adrenocorticotropin hormone (ACTH), melanocyte stimulating hormone, atrial natriuretic peptide, and plasma concentrations of sodium and potassium, and by a multi-step pathway called the renin-angiotensin-aldosterone (RAA) system. Aldosterone receptors are proteins that initially reside in the cytoplasm of certain types of cells, such as smooth muscle cells and fibroblasts in the aorta. When an aldosterone receptor is activated by aldosterone, the receptor/aldosterone complex is transported into the cell nucleus, where it binds to nuclear chromatin and presumably causes an alteration in the transcription of genes that encode proteins which are involved in the retention of sodium and water by the body. Aldosterone levels decrease with age and its release in older adults is less responsive to upright posture or decreased sodium intake than in younger adults.
An aldosterone test measures the amount of aldosterone in serum (blood). This test is performed to investigate hard-to-control blood pressure, orthostatic hypotension and certain fluid and electrolyte disorders. Aldosterone measurement is useful in detecting a condition called aldosteronism, which is caused by excess secretion of the hormone from the adrenal glands. Frequently, blood aldosterone levels are combined with other blood tests (plasma renin activity) or provocative tests (captopril test, intravenous saline infusion test or ACTH infusion test) in order to diagnosis over- or under-production of the hormone. There are two types of aldosteronism: primary and secondary. Primary aldosteronism is most commonly caused by an adrenal tumor, as in Conn's syndrome. Secondary aldosteronism is more common and may occur with congestive heart failure, cirrhosis with fluid in the abdominal cavity (ascites), certain kidney diseases, excess potassium, sodium-depleted diet, and toxemia of pregnancy. |
