when the level of antidiuretic hormone increases
Changes in blood pressure and volume are not nearly as sensitive a stimulator as increased osmolarity, but are nonetheless potent in severe conditions. For example, Loss of 15 or 20% of blood volume by hemorrhage results in massive secretion of antidiuretic hormone.
Increased ADH levels are often associated with SIADH, which may be due to a variety of cancers, including leukemia, lymphoma, and cancers of the lung, pancreas, bladder, and brain. Levels of ADH may be greatly increased with such cancers.