Antidiuretic hormone (also known as vasopressin) is a 9-peptide hormone secreted by nerve cells in the supraoptic and paraventricular nuclei of the hypothalamus and released after reaching the pituitary gland via the hypothalamic-pituitary bundle. Its main role is to improve the water permeability of the distal convoluted tubules and collecting ducts, promote water absorption, and is a key regulatory hormone for urine concentration and dilution. In addition, the hormone also enhances the permeability of the collecting ducts of the inner medulla to urea. After drinking large amounts of water, blood is diluted, crystal osmolarity decreases, and antidiuretic hormone secretion is reduced. What can be done to prevent reduced secretion of antidiuretic hormone (ADH)? Changes in plasma crystal osmolarity can significantly affect the secretion of antidiuretic hormone. Heavy sweating. When the body loses water due to severe vomiting or diarrhea, the plasma crystal osmolarity increases, which can cause an increase in the secretion of antidiuretic hormone, resulting in a significant increase in the reabsorption of water by the kidneys, leading to a concentration of urine and a decrease in urine output. On the contrary, after drinking large amounts of water, urine is diluted and urine volume increases, thus allowing excess water to be excreted from the body. Hemodilution and lower crystal osmolarity are responsible for the decrease in antidiuretic secretion. The main prevention method is to control the amount of water intake. For example, after a normal person drinks 100ml of water at a time, the volume of urine starts to increase after about half an hour, and by the end of the first hour, the volume of urine can reach its highest value; then the volume of urine decreases and returns to its original level after 2-3 hours. If isotonic saline (0.9 NaCI solution) is consumed, the urine output does not show the same changes as after drinking clear water. This phenomenon of increased urine output caused by drinking large amounts of clear water is called hydronephrosis, and it is a common test used clinically to test the diluting capacity of the kidneys.