Mineralocorticoids

RECEPTORS:
  • Mineralcorticoid receptors are expressed at high levels in renal distal tubules and cortical collectiong ducts and in other mineralocorticoid target tissues such as salivary glands and the colon. 
  • It is also found in multiple sites in the brain (hippocampus), myocardium, peripheral vasculature, brown adipose tissue and sweat glands.
  • Mineralcorticoid receptors are located mainly in the cytoplasm.
TYPES:
  • Mineralocorticoids are:

  1. Aldosterone(most potent)r> 
  2. 11-deoxycorticosterone
ACTIONS:
  • 90% of mineralocorticoid activity is provided by aldosterone
  • It is very essential for life and it maintains the osmolarity and volume of ECF.
  • It is usually called life-saving hormone because, its absence causes death within 3 days to 2 weeks. 
  1. Aldosterone has three important functions:
  2. Reabsorption of sodium from renal tubules
  3. Excretion of potassium through renal tubules
  4. Secretion of hydrogen into renal tubules.
  5. On Sodium Ions:
  6. Acts on the distal convoluted tubule and the collecting duct and increases the reabsorption of sodium. 
  • On Extracellular Fluid Volume:
  1. When sodium ions are reabsorbed from the renal tubules, simultaneously water is also reabsorbed so the concentration of sodium in the body does not increase very much The diuretic group that does not require access to the tubular lumen to induce diuresis is Mineralocorticoid antagonist
  • On Blood Pressure
  1. Increase in ECF volume and the blood volume finally leads to increase in blood pressure.
  2. Aldosterone escape/Escape phenomenon
  3. It refers to escape of the kidney from salt-retaining effects of excess administration or secretion of aldosterone, as in the case of primary hyperaldosteronism
  • On Potassium Ions:
  1. It increases the potassium excretion through the renal tubules. 
  2. Gitelman syndrome(hypokalemia )
  • On Hydrogen Ion Concentration:
  1. While increasing the sodium reabsorption from renal tubules, aldosterone causes tubular secretion of hydrogen ions.
  2. To some extent, secretion of hydrogen ions is in exchange for sodium ions.
  3. It obviously reduces the hydrogen ion concentration in the ECF. 
  • On Sweat Glands and Salivary Glands:
  1. Sodium is reabsorbed from sweat glands under the influence of aldosterone, thus the loss of sodium from the body is prevented.
  2. Same effect is shown on saliva also. 
  • Intestine:
  1. It increases sodium absorption from the intestine, especially from colon and prevents loss of sodium through feces.
 MODE OF ACTION
  • Acts through the messenger RNA (mRNA) mechanism.
  • Least mineralocorticoid activity is seen in Methylprednisolone,Dexamethasone & Triamcinolone
  • Apparent mineralocorticoid excess is d/t inhibition or absence of /V hydroxysteroid dehydrogenase type 2Q AME syndrome & 11 HSD type 2
  • Spironolactone is a mineralocorticoid antagonist 
  • Mineralocroticoid with no glucocorticoid activity —> Desoxycorticosterone acetate (DOCA)
  • Fludrocortisone have max mineralocorticoid activity
SIDE EFFECTS:
  • Fluid retention and hypertension.
  • Edema,
  • Progressive rise in BP, 
  • Hypokalemia and alkalosis
  • The diuretic induced hypokalemia is aggravated
  • Promote CHF associated myocardial fibrosis and progression of the disease
Exam Question
  • Mineralocorticoid receptors are present in Hippocampus, Kidney, Colon
  • Metabolic alkalosis is seen in Primary mineralocorticoid excess
  • Mineralocorticoid deficiency causes metabolic acidoosis
  • Mechanism of hypokalemia in Gitelman syndrome is Mineralocorticoid excess
  • Apparent mineralocorticoid excess is due to 11-13 hydroxysteroid dehydrogenase
  • LeastLeast Mineralocorticoid activityis seen in Methylprednisolone,Dexamethasone and Triamcinolone
  • Spironolactone is a mineralocorticoid antagonist
  • The diuretic group that does not require access to the tubular lumen to induce diuresis is Mineralocorticoid antagonist
  • Most potent mineralocorticoid is Aldosterone
  • Mineralocorticoid with no glucocorticoid activity —> Desoxycorticosterone acetate (DOCA)..
Don't Forget to Solve all the previous Year Question asked on Mineralocorticoids