The mineralocorticoids are a group of steroid hormones produced by the adrenal cortex. Their major effect is within the kidney, but they affect many tissues e.g. sweat glands, gallbladder, gastrointestinal tract.
They bind to receptors in the cytosol of the renal distal convoluted tubule before passing into the nucleus. Within the nucleus, they regulate the production of proteins which may have one of the following effects:
- the sodium pump theory: the protein increases the activity of the Na+/K+ ATPase on the capillary side of the cell to increase active sodium reabsorption into the peritubular space and hence the blood. In tandem, potassium is transferred into urine. Water passively follows sodium.
- the permease theory: increase the number sodium channels across the apical membrane of the cell, so increasing passive sodium movement inwards.
- the metabolic theory: increased supply of ATP from mitochondria to power the Na+/K+ ATPase with increased sodium transit inwards
The overall effect is to promote an increase in intravascular volume and plasma sodium with a reduction in plasma potassium.
Endogenous control of mineralocorticoid release is largely dependent on the renin-angiotensin system.
Examples include endogenous aldosterone, corticosterone and 11-desoxycorticosterone. A synthetic example is fludrocortisone.