Adiuretin

Adiuretin

Adiuretin, also known as antidiuretic hormone (ADH) or vasopressin, is a peptide hormone that plays a crucial role in regulating the body's retention of water and maintaining blood pressure. It is synthesized in the hypothalamus and released by the posterior pituitary gland. This hormone acts primarily on the kidneys to promote water reabsorption, thereby concentrating the urine and reducing urine volume.

Structure and Synthesis

Adiuretin is a nonapeptide, meaning it consists of nine amino acids. It is synthesized in the hypothalamus, specifically in the supraoptic and paraventricular nuclei. Once synthesized, it is transported down the axons of the hypothalamic neurons to the posterior pituitary gland, where it is stored and eventually released into the bloodstream.

Function

The primary function of adiuretin is to regulate water balance in the body. It achieves this by increasing the permeability of the kidney's collecting ducts to water. This action is mediated through the binding of adiuretin to V2 receptors on the cells of the collecting ducts, which triggers a signaling cascade that results in the insertion of aquaporin-2 water channels into the apical membrane of these cells.

In addition to its renal effects, adiuretin also has vasoconstrictive properties, which can increase blood pressure. This effect is mediated through V1 receptors located on vascular smooth muscle cells.

Regulation

The secretion of adiuretin is primarily regulated by plasma osmolality and blood volume. An increase in plasma osmolality, detected by osmoreceptors in the hypothalamus, stimulates the release of adiuretin. Conversely, a decrease in blood volume or blood pressure, detected by baroreceptors, also triggers adiuretin release.

Clinical Significance

Disorders of adiuretin secretion or action can lead to various clinical conditions. For example, insufficient secretion of adiuretin results in diabetes insipidus, characterized by excessive urination and thirst. Conversely, excessive secretion of adiuretin can lead to the syndrome of inappropriate antidiuretic hormone secretion (SIADH), which causes water retention and hyponatremia.

Also see

• Hypothalamus
• Posterior pituitary gland
• Diabetes insipidus
• Syndrome of inappropriate antidiuretic hormone secretion
• Aquaporin