Final answer:
ADH helps maintain blood homeostasis by increasing the reabsorption of water into the bloodstream, which dilutes the sodium concentration and lowers blood osmolarity, returning levels to normal.
Step-by-step explanation:
Based on the provided information, the most likely role of antidiuretic hormone (ADH) in maintaining blood homeostasis is to promote an increase in the movement of water into the bloodstream. When the concentration of sodium in the blood increases, it triggers the release of ADH, which then acts on the kidneys to insert aquaporins into the collecting ducts and tubules, making them more permeable to water. This action results in an increased reabsorption of water into the blood, thus diluting the sodium concentration and decreasing blood osmolarity. As the osmolarity falls back to normal levels, feedback mechanisms result in a reduced secretion of ADH, thus achieving homeostasis.