Antidiuretic hormone, typically called ADH, reduces the amount of urine production and can also release water from the kidneys back into the circulatory system. Osmoreceptors, a type of sensory neuron, measure the concentration of certain chemicals in a human's bloodstream, and if the concentrations are too high, ADH is released. ADH then connects to and opens kidney cell receptors to allow water to dilute the blood.
Substances can be diuretic, antidiuretic or neither. Diuretics are often administered in medical settings in order to promote urine creation, which will expel excess electrolytes. The main purpose of this, according to WebMD, is to thin out blood to lower blood pressure. Diuretics can be used to treat a variety of heart conditions.