4. What is the mechanism that the peptide hormone ADH (antidiuretic hormone) stimulates water reabsorption in the kidney collecting ducts? In diabetes insipidus, the kidneys are unable to conserve water. One heritable form of the disease, central diabetes insipidus, can be treated by desmopressin, a synthetic replacement for ADH. Another heritable form of the disease, nephrogenic diabetes insipidus, does not respond to treatment with desmopressin. Hypothesize in which components might have been affected by the mutations in the two forms of the disease.