What is the principal cause of vasopressin?

ADH/ vasopressin secreted from Hypothalamus Acts on Collecting duct in Kidney ADH primarily affects the ability of the kidney to reabsorb water; when present, ADH induces expression of water transpo proteins in the late distal tubule and collecting duct to increase water reabsorption. Hyperosmolar states most strongly trigger its release. Therefore, slight elevations in osmolarity result in the secretion of ADH. ADH then acts primarily in the kidneys to increase water reabsorption, thus returning the osmolarity to baseline. NOTE: ADH secretion also occurs during states of hypovolemia or volume depletion, but main principal is Hyperosmolarity.