Potassium ions aldosterone

Adrenocorticoid hormones are produced in the adrenal glands. They regulate a variety of metaholic processes. The most important mineralo-corticoid is aldosterone, an aldehyde as well as a ketone, which regulates the reahsorption of sodium and chloride ions in the kidney, and increases the loss of potassium ions. Aldosterone is secreted when hlood sodium ion levels are too low to cause the kidney to retain sodium ions. If sodium levels are elevated, aldosterone is not secreted, so some sodium will he lost in the urine and water. Aldosterone also controls swelling in the tissues. 

The mechanism by which potassium regulates aldosterone secretion is unclear however, this ion appears to have a direct effect on the adrenal cortex. An increase in the level of potassium in the blood stimulates the release of aldosterone. The effect of aldosterone on the kidney then decreases the level of potassium back to normal. 

Triamterene is a pyrazine derivative that inhibits reabsorption of sodium ions without increasing excretion of potassium ions. It exhibits the same approximate effect as spironolactone however, it does not competitively bind with aldosterone receptors. Its action does not have an effect on secretion of aldosterone or its antagonists, which are a result of direct action on renal tubules. 

Aldosterone increases sodium reabsorplion in the kidney.s. An increase in plasma srxiium concentration, in turn, will lead to increased blood volume, becau.se blood volume and urinary excretion of water arc directly related to the plasma srxiium concentration. Simultancou.sly. aldosterone in-crca.ses potassium ion excretion. 11-Deoxycorticosterone also is quite active as a minetalrx orticoid. Similar actions are exhibited with hydrocortisone and corticosterone, but to a much smaller degree. 

The major regulators of aldosterone secretion are the renin-angiotensin system and extracellular potassium ions (K+). The former is sensitive to changes in intravascular volume and arterial pressure, while the latter is an aldosterone-regulated substance that feeds back to reduce aldosterone synthesis (simple negative feedback). Aldosterone secretion is also influenced (but not regulated) by ACTH and, directly and indirectly, by atrial natriuretic factor (ANF). 

Potassium ions exert a direct, stimulatory effect on aldosterone secretion that is independent of the renin-angiotensin system. Small increases in serum potassium elicit a rise in serum aldosterone levels, whereas small decreases in serum potassium result in reduced levels of serum aldosterone. Aldosterone, by promoting the... 

General. Noteworthy reports- and reviews pertaining to the pharma-cologicalj endocrinological > and clinical aspects of diuretics have appeared in the recent literature. The use of diuretics in the treatment of hypertension has been reviewed with especial emphasis on the hypotensive action of the aldosterone antagonist, spironolactone.° Fundamental studies on the mechanism of transport of electrolyte across the tubular epithelium have indicated that phospholipids may play a critical role. Phospholipase C and pancreatic lipase markedly reduced the rate of reabsorption of saline droplets infused into rat proximal tubules. Likewise, phospholipase C reduced the ability of extractable lipids to bind sodium and potassium ions in rat kidney homogenates whereas, phospholipase D and ribonuclease appear to enhance cation binding. ... 

Some of the rare causes of metabolic alkalosis due to potassium depletion are those found in subjects with either Cushing s syndrome, primary aldosteronism, or Bartter s syndrome. In Cushing s syndrome, the potassium ions and alkalosis are related to increased mineralocorticoid activity resulting from an increase in adrenocorticotropic hormone (ACTH), cortisol, deoxycorticosterone, and corticosterone. In primary aldosteronism, the effects of increased aldosterone are manifest on the distal tubule of the kidney. In Bartter s syndrome, the basic abnormality appears to be a defect in the reabsorption of chloride in the ascending limb of loop of Henle, leading to loss of potassium (12). 

Aldosterone decreases urinary sodium excretion by increasing sodium reabsorption in the renal tubules at the expense of potassium and hydrogen ions. Aldosterone also stimulates sodium conservation by the sweat glands and the... 

Other mineralocorticoids have an effect on the electrolytic balance of the body, but aldosterone is the most potent. Its ability to cause increased reabsorption of sodium and chloride ion and increased potassium ion excretion is approximately 3.000-fold that of hydrocortisone. A substance that antagonizes the effects of aldosterone could conceivably be a good diuretic drug. Spironolactone is such an antagonist. 

These observations on the effect of body fluid volumes and electrolyte concentrations on aldosterone secretion may have some bearing on the pathogenesis of classical clinical changes. For example, in renal tubular acidosis there is an obligatory sodium loss. The plasma potassium levels are decreased, and aldosterone secretion is stimulated. The administration of bicarbonate, a procedure which usually leads to potassium diuresis, induces potassium retention in these cases. To explain such intricate interactions between hormonal secretion, body fluid volume, and ion concentration, one could assume that the sodium loss, which is obligatory in renal acidosis, leads to reduction in the body fluid volume followed by a loss of potassium. The administration of bicarbonate, which prevents sodium loss and thereby influences the body fluid volume, reduces aldosterone secretion and prevents the loss of potassium ions. 

The main endogenous mineralocorticoid is aldosterone, which is mainly produced by the outer layer of the adrenal medulla, the zonaglomerulosa. Aldostorone, like other steroids, binds to a specific intracellular (nuclear) receptor, the mineralocorticoid receptor (MR). Its main action is to increase sodium reabsotption by an action on the distal tubules in the kidney, which is accompanied by an increased excretion of potassium and hydrogen ions. 

Potassium-sparing diuretics are often coadministered with thiazide or loop diuretics in the treatment of edema and hypertension. In this way, edema fluid is lost to the urine while K+ ion balance is better maintained. The aldosterone antagonists are particularly useful in the treatment of primary hyperaldosteronism. 

Potassium secretion is enhanced by aldosterone. As the concentration of K+ ions in the extracellular fluid increases, the secretion of aldosterone from the adrenal cortex also increases. The mechanism of action of aldosterone involves an increase in the activity of the Na+, K+ pump in the basolateral membrane. Furthermore, aldosterone enhances formation of K+ channels in the luminal membrane. 

Amyloride is also a potassium sparing diuretic that exhibits moderate activity. It is not an antagonist of aldosterone. It inhibits reabsorption of sodium ions and reduces excretion of... 

Aldosterone and other steroids with mineralocorticoid properties promote the reabsorption of sodium from the distal part of the distal convoluted tubule and from the cortical collecting renal tubules, loosely coupled to the excretion of potassium and hydrogen ion. Sodium reabsorption in the sweat and salivary glands, gastrointestinal mucosa, and across cell membranes in general is also increased. Excessive levels of aldosterone produced by tumors or overdosage with synthetic mineralocorticoids lead to hypokalemia, metabolic alkalosis, increased plasma volume, and hypertension. 

Aldosterone secretion is also stimulated by increased plasma potassium concentration. Potassium is secreted into the urine in exchange for reabsorption of sodium in the distal nephron. Aldosterone also promotes secretion of hydrogen ions from the distal tubule according to the acid-base status of the... 

In the distal tubule (site 4), sodium ions are exchanged for potassium and hydrogen ions. The sodium ions are transported across the epithelial Na chaimel (called ENaC), which is stimulated by aldosterone. The aldosterone (mineralocorticoid)... 

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