Stimulates retention of water by kidneys?

The hormone that stimulates retention of water by kidneys is called vasopressin, also known as antidiuretic hormone (ADH). It is produced by the hypothalamus and released by the pituitary gland in response to changes in blood osmolality and blood pressure. Vasopressin acts on the kidneys by increasing the permeability of the collecting ducts to water, allowing more water to be reabsorbed from the urine and retained in the body. This helps to maintain blood volume and blood pressure, as well as prevent dehydration.