Hormones aldosterone

The volume of extracellular fluid is direcdy related to the Na" concentration which is closely controlled by the kidneys. Homeostatic control of Na" concentration depends on the hormone aldosterone. The kidney secretes a proteolytic enzyme, rennin, which is essential in the first of a series of reactions leading to aldosterone. In response to a decrease in plasma volume and Na" concentration, the secretion of rennin stimulates the production of aldosterone resulting in increased sodium retention and increased volume of extracellular fluid (51,55). 

Sodium reabsorption Much less than 10% of the filtered load of NaCl reaches the distal nephron. Regulation of Na uptake, occurring mainly in the principal cells of the cortical collecting tubule, is controlled by the steroid hormone aldosterone (see Section 4.4). The net effect of aldosterone is the reclamation of NaCl and potassium excretion in to the luminal fluid. 

The steroid hormone aldosterone (see p. 55) increases Na reuptake, particularly in the distal tubule, while atrial natriuretic peptide (ANP) originating from the cardiac atrium reduces it. Among other effects, aldosterone induces Na /K" ATPase and various Na" transporters on the luminal side of the cells. 

Secretion of adrenocortical steroids is controlled by the pituitary release of corticotropin (ACTH). Secretion of the salt-retaining hormone aldosterone is primarily under the influence of angiotensin. Corticotropin has some actions that do not depend on its effect on adrenocortical secretion. However, its pharmacologic value as an anti-inflammatory agent and its use in testing adrenal function depend on its secretory action. Its pharmacology is discussed in Chapter 37 and is reviewed only briefly here. 

Angiotensin II has a variety of effects. By constricting blood vessels it raises blood pressure, and by stimulating thirst centers in the brain it increases blood volume. Both angiotensins II and III also act on the adrenal gland to promote the synthesis and release of aldosterone. Most of the effects of angiotension II are mediated by 359-residue seven-helix G-protein linked receptors which activate phospholipase C.p q qr Like other steroid hormones aldosterone acts,via mineralocorticoid receptors, to control transcription of a certain set of proteins. The end effect is to increase the transport of Na+ across the renal tubules and back into the blood. Thus, aldosterone acts to decrease the loss of Na+ from the body. It promotes retention of water and raises... 

The key to subcutaneous water control depends upon control of the hormone Aldosterone. Obviously estrogen control is part of this hormone cascade action/reaction factor. But, our main focus is salt and water control, so Aldosterone is the key. 

Spironothiazid is a diureteic and an ALDOSTERONE antagonist. This means that it suppresses the water retaining actions of the hormone ALDOSTERONE while lowering water retention by lowering electrolytes (potassium, sodium, and calcium). The advantage of the combination is that the potassium absorption effect by the spironolactone can be mediated by the hydrochlorthiazide. Because of this, some of the potassium loss side effects can be avoided. This is probably a safer choice than LASIX though any diuretic use should be medically monitored. Thiazides also lead to a lower loss of calcium. 

Metabolites and substrates (urea, triglycerides, bili-rubine, lactate), enzymes (the measurands are the enzyme activities), hormones (aldosterone, estradiol, es-triol, testosterone, thyroxin), drugs (theophylline, digoxin, digitoxin), total proteinAs far as possible, isotope dilution mass spectrometry is used for the primary measurements in both institutes (e.g. [4]). 

Spironolactone competitively inhibits the physiologic effects of the adrenocortical hormone aldosterone on the distal tubules, thereby producing increased excretion of sodium chloride and water, and decreased excretion of potassium, ammonium, titratable acid, and phosphate. Spironolactone is a potassium-sparing diuretic that has diuretic activity only in the presence of aldosterone, and its effects are most pronounced in patients with aldosteronism. Spironolactone does not interfere with renal tubular transport mechanisms, and does not inhibit carbonic anhydrase. 

The book explores the invention of new chemical reactions for use in the synthesis of biologically and economically important compounds. It begins with a mechanistic study of the industrial importance of the pyrolysis of chlorinated alkanes. It continues with a theory on the biosynthesis of phenolate derived alkaloids involving phenolate radical coupling. Included in the book is a description of the work on nitrite photolysis (the Barton Reaction) which involved the invention of new radical chemistry leading to a simple synthesis of the hormone, aldosterone. In two final chapters Dr Shyamal Parekh views Professor Barton s pioneering work from the modern perspective, with a review of recent applications in industry and research. 

Q4 Potassium concentration is mainly controlled by the steroid hormone aldosterone. Aldosterone release from the adrenal cortex can be stimulated by either decreased plasma sodium or by increased plasma potassium concentration. An increase in aldosterone secretion causes retention (reabsorption) of sodium in the distal nephron in exchange for secretion of potassium into the urine. The amount of potassium excreted by the kidney is influenced by the acid-base status of the body. In alkalosis, potassium excretion increases, whereas in acidosis it is decreased. In the distal nephron H+ and K+ compete for excretion in exchange for the reabsorption of sodium. Insulin also affects plasma potassium concentration because it promotes the movement of potassium from the plasma into cells. 

Aldosterone acts in the connecting segments and collecting ducts to increase the reabsorption of sodium and chloride ions and promote the excretion of potassium and hydrogen ions. As with all steroid hormones, aldosterone acts by diffusing into the tubular cells and attaching to specific cytosolic receptors. These complexes are... 

The fact that most of the Holarrhena alkaloids are characterized by substitution in position 18 was utilized for preparation of a series of nitrogen-free, 18-substituted steroids, which are of interest in relation to the adrenocortical hormone aldosterone. A detailed description would be beyond the scope of this summary. However, since some steps in these syntheses constitute interesting reactions of Holarrhena alkaloids, a brief outline, dealing with the principles of these procedures, will be presented here. 

ALDOSTERONE ANTAGONISTS (e.g. potassium canrenoate and spironolactone) work by blocking the action of the hormone aldosterone (a MINERALOCORTICOId), and this makes them suitable for treating oedema associated with aldosteronism, liver failure and certain heart conditions. 

Sodium is freely filtered by the glomeruli. Seventy to 80% of the filtered Na" load is then actively reabsorbed in the proximal tubules, with 01 and water passively following in an isoosmotic and electrically neutral manner. Another 20% to 25% is reabsorbed in the loop of Henle along with Cl" and more water. In the distal tubules, interaction of the adrenal hormone aldosterone with the coupled Na -K and Na -H exchange systems directly results in the reabsorption of Nah and indirectly of d , from the remaining 5% to 10% of the filtered load. It is the regulation of this latter fraction of filtered Na that primarily determines the amount of Na excreted in the urine. These processes are discussed in detail in Chapter 45. 

The steroid hormone aldosterone, synthesized in the zona glomerulosa of the adrenal cortex, also plays an important role in maintaining blood osmolar-ity. It binds its receptors in the cytoplasm of epithelial cells of the distal colon and the renal nephron, followed by translocation of the hormone-receptor complex to the nucleus and activation of transolption of ion transport genes to increase Na reabsorption and secretion. Water follows Na+ movement by osmosis. These transporters include the luminal amiloride-sensitive epilheUal Na+ channel, the luminal channel, the serosal Na, K+-ATPase, the Na+/H+exchanger, and the NaVCT cotransporter. 

The hormones of (he adrenal glands are essential for survival. The adrenal cortex is the source of the two important steroid hormones, aldosterone and cortisol (Fig. 1). The adrenal medulla is embryologically and histologically distinct from the cortex anil is part of the sympathetic nervous system. Medullary cells synthesize, store and secrete adrenaline, along with noradrenaline and dopamine. The adrenal medullary hormones arc discussed further on pages 126-127. 

Mineralocorticoids are a class of steroid hormones that includes the hormone aldosterone (Figure... 

Fig. 4.10. Body fluid homeostasis (constant body water balance). Intake is influenced by availability of fluids and food, thirst, hunger, and the ability to swallow. The rates of breathing and evaporation and urinary volume influence water loss. The body adjusts the volume of urinary excretion to compensate for variations in other types of water loss and for variations in intake. The hormones aldosterone and antidiuretic hormone (ADH) help to monitor blood volume and osmolality through mechanisms regulating thirst and sodium and water balance.

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