General characteristics and regulation
The endogenous precursors and hormones in this group are aldosterone (the primary mineralocorticoid) and desoxycortone. Their secretion is regulated by adrenocorticotropic hormone (ACTH).
At normal salt intake, the daily secretion of aldosterone is 100–200 µg, and desoxycortone is about 200 µg. The hormones have a short half-life: aldosterone is eliminated in 15–20 minutes, and desoxycortone in 70 minutes. Aldosterone is transported bound to plasma proteins. The bulk of metabolites is excreted by the kidneys: 70% as a conjugate (tetrahydroaldosterone) and 30% in free form or as 3-oxoglucuronide.
Mechanism of action and physiological effects
The molecular mechanism is based on interaction with specific mineralocorticoid receptors located in the cytoplasm of target cells.
- Main sites of action: kidneys (terminal part of the distal tubules and cortical collecting ducts).
- Extrinsic targets: sweat and salivary glands, as well as the gastrointestinal mucosa.
The main pharmacodynamic effect consists in stimulating the reabsorption of sodium ions (Na+) and increasing the excretion of potassium ions (K+).
Pharmacology of desoxycortone acetate
Desoxycortone acetate is a synthetic analogue. Its pharmacological features:
- Mechanism: stimulates the synthesis of the sodium carrier protein in the liver.
- Selectivity: the drug has virtually no effect on carbohydrate metabolism (no pronounced glucocorticoid activity) and does not affect pigmentation, estrogenic, or androgenic functions.
- Indications: acute and chronic adrenal insufficiency, general muscular weakness (myasthenia).
- Contraindications: congestive heart failure, arterial hypertension, atherosclerosis, as well as severe hepatic and renal diseases.
Characteristics of fludrocortisone and dose-dependency
Fludrocortisone (known under the trade name Cortineff) is a potent steroid with a mixed activity profile, combining mineralocorticoid and glucocorticoid properties.
Effects depend on the administered dose:
- Low doses (0.1 mg 2–7 times a week) exhibit pronounced mineralocorticoid activity.
- High doses lead to the appearance of glucocorticoid properties.
The drug is the most widely used mineralocorticoid and is employed as a sodium-retaining agent primarily in chronic adrenocortical insufficiency in combination with hydrocortisone.
Briefly: answers to topical questions
What factors and systems physiologically regulate aldosterone secretion?
Aldosterone secretion is regulated by adrenocorticotropic hormone. When circulating blood volume decreases, for example due to blood loss, vomiting, or diarrhea, the renin-angiotensin-aldosterone system is activated, leading to secondary aldosteronism.
What side effects can occur with long-term use of mineralocorticoids?
Long-term use of mineralocorticoids leads to water and electrolyte disorders associated with excessive sodium retention and potassium loss.
- Water and sodium retention — leads to pronounced edema and the development or exacerbation of arterial hypertension.
- Hypokalemia — causes general muscular weakness and various cardiac arrhythmias.
How do mineralocorticoids affect the acid-base balance of the blood?
Mineralocorticoids promote the development of metabolic (excretory) alkalosis due to alterations in electrolyte balance.
- Excretion of hydrogen ions — the hormones directly enhance renal excretion of hydrogen and ammonium ions.
- Hypokalemia — increased potassium excretion lowers its blood levels, which activates proton transport into cells and increases their secretion into primary urine.
- Sodium retention — aldosterone enhances sodium reabsorption in the renal tubules, which further exacerbates alkalosis.
Na K: Mineralocorticoids retain Sodium (sodium comes in) and excrete Potassium (potassium goes out).
Class and exam questions
Which gland regulates mineralocorticoid secretion?
Mineralocorticoid secretion is regulated by adrenocorticotropic hormone (ACTH).
What are the main extrinsic targets of mineralocorticoids?
Extrinsic targets include the sweat and salivary glands, as well as the gastrointestinal mucosa.
What is the peculiarity of fludrocortisone's action depending on the dose?
At low doses, the drug exhibits pure mineralocorticoid activity, whereas at high doses its glucocorticoid properties are activated.
What else to study on this topic
- Pharmacokinetics and metabolism of aldosterone in the liver and kidneys
- The role of the sodium carrier protein in epithelial cells of the distal tubules
- Clinical manifestations of hyperaldosteronism and hypoaldosteronism
- Interaction of fludrocortisone with hydrocortisone in replacement therapy
- Mineralocorticoid receptor antagonists and steroid synthesis inhibitors
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