Antidiuretic refers to a substance or hormone that promotes the reabsorption of water in the renal tubules and collecting ducts of the kidney, leading to an increased concentration of urine and a reduction in urine output. The primary antidiuretic hormone is antidiuretic hormone (ADH), also known as vasopressin.
ADH is produced by the hypothalamus and stored in the posterior pituitary gland. When the body senses an increase in plasma osmolality (the concentration of solutes in the blood) or a decrease in blood volume, ADH is released into the bloodstream, where it travels to the kidney and binds to specific receptors on the cells of the collecting ducts. This binding stimulates the reabsorption of water from the filtrate in the renal tubules, increasing the concentration of urine and reducing urine output.
In this way, ADH helps to regulate the fluid and electrolyte balance in the body, as well as blood pressure. The action of ADH is opposed by the hormone aldosterone, which promotes the reabsorption of ions such as sodium and potassium and the excretion of water.
Disorders of the hypothalamic-pituitary-renal axis can result in imbalances in the production and release of ADH, leading to conditions such as diabetes insipidus, in which there is an excessive production of dilute urine, and SIADH (syndrome of inappropriate antidiuretic hormone secretion), in which there is an excessive production of concentrated urine. These disorders can result in imbalances in fluid and electrolyte balance and can lead to a variety of health problems.