ADH, also known as vasopressin or antidiuretic hormone, is formed in the hypothalamus and stored in the posterior lobe of the pituitary gland. From there, it continues to the neurohypophysis before ending up in the bloodstream. It helps regulate the amount of water in the body by controlling the amount of water the kidneys excrete. In this article, we will take a closer look at the properties and effects of ADH.
It is an oligopeptide formed by the union of 9 amino acids. This hormone consists of the amino acids cysteine, tyrosine, glutamine, proline, an amino group, phenylalanine, arginine, asparagine and a carboxyl group.
The function of ADH
Although the main function is to regulate the activity of the kidneys, it also has a certain effect on the central nervous system and the cardiovascular system, among other things.
This hormone is released in response to the hypertension of body fluids. This helps the kidneys reabsorb water and return it to the blood from the distal tubules of the kidneys, which normalizes the tonicity of the body fluids.
As a consequence of renal reabsorption, urine becomes more concentrated and decreases in volume. When ADH comes out in high concentrations , it can increase blood pressure as it induces moderate vasoconstriction.
The effects of ADH
On the kidneys
The effect it has on the kidneys refines a number of processes that concentrate the urine. By promoting this concentration, ADH produces a net absorption of free water into the extracellular fluid.
The effect ADH has on the kidneys gives rise to three main effects:
- It increases water permeability in initial and cortical manifolds. In addition, it increases the internal and external medullary tract in the kidneys. The water is reabsorbed and more concentrated urine is excreted.
- In addition, it increases the permeability of the inner marrow portion of the collecting duct to the uric acid.
- Finally, salt uptake is increased through the ascending portion of the Henle loop.
The effects of ADH on the central nervous system
The antidiuretic hormone that is released from hypothalamic neurons has to do with the regulation of blood pressure and temperature. It has been proven that this hormone can have analgesic effects depending on gender and stress.
ADH is a powerful vasoconstrictor that can increase systemic vascular resistance, which explains the hormone’s original name “arginine vasopressin”.
How does ADH regulate itself?
The release of ADH is usually controlled by the osmolarity of the extracellular fluid. The decrease in osmolarity reduces the secretion of ADH, at the same time as an increase in osmolarity increases the secretion of ADH.
Receptors in the heart and large blood vessels detect low blood pressure or a decrease in blood volume. This happens when the body bleeds or during dehydration. Under these circumstances, they stimulate the release of vasopressin.
Antidiuretic hormone secretion also occurs if the concentration of salts in the bloodstream increases. Similarly, one will experience hyponatremia if the concentration of salts becomes abnormally low.
The antidiuretic hormone is also released in case of thirst, nausea, vomiting and pain. It is therefore important to maintain the fluid level in the bloodstream during periods of stress or when one is injured.
What happens if the body has excessive ADH?
High levels of this hormone promote water retention in the body via the kidneys. This is a condition known as SIADH syndrome ( syndrome of inappropriate secretion of antidiuretic hormone in English).
In patients suffering from this syndrome, excessive amounts of ADH are released when they do not need it. This results in excessive water retention which dilutes the blood, giving a characteristically low salt concentration.
Excessive levels of this hormone can occur as a side effect of certain medications, as well as diseases of the lungs, chest wall, hypothalamus and pituitary gland.
What if we have almost no ADH?
Low levels of the antidiuretic hormone will cause the kidneys to excrete excess water. Urine volume will increase, which will lead to dehydration and a reduction in blood pressure. Low levels of this hormone may indicate damage to the hypothalamus, pituitary gland or primary polydipsia.
Vasopressin positions itself as an excellent therapeutic alternative alone or in combination with other vasopressors in the daily practice of intensive care.