Mr. Metzner has polyuria with a urine volume of 8 L/day. His urine specific gravity is 1.002. His serum sodium (Na+) is 150, and his plasma osmolality is 300 mOsm/kg. He is always asking for more cold liquids to drink. What type of hormonal alteration is Mr. Metzner exhibiting? What are some possible causes of this alteration?