What is the hormone that signals kidney to make less urine?

The hormone that signals the kidneys to make less urine is called antidiuretic hormone (ADH), also known as vasopressin. ADH is produced by the hypothalamus and stored in the pituitary gland. When the body senses a decrease in blood volume or an increase in blood osmolality, the hypothalamus releases ADH. ADH then travels to the kidneys and acts on the collecting ducts, increasing water reabsorption and reducing urine output. This helps to maintain blood volume and prevent dehydration.