Final answer:
If a person could not synthesize vasopressin, the urine would become hypoosmotic to plasma due to the inability of the kidneys to reabsorb water in the collecting ducts, leading the body to produce more dilute urine.
Step-by-step explanation:
If a person lost the ability to synthesize vasopressin, also known as antidiuretic hormone (ADH), the most likely outcome would be option E: the urine would become hypoosmotic compared to plasma. Without vasopressin, the kidneys would not be able to reabsorb water efficiently in the collecting ducts, because vasopressin stimulates the insertion of aquaporin water channels, allowing water to be reabsorbed into the bloodstream. The lack of water reabsorption would lead to increased urine volume, and the urine would be more diluted, or hypoosmotic, compared to the plasma.
Regulation of urine volume and osmolarity are major functions of the collecting ducts, which are controlled by ADH. If vasopressin/ADH were not present, despite other mechanisms that reabsorb water and electrolytes, the specific function of water reabsorption in the collecting ducts would be compromised, leading to the production of more dilute urine as the body loses the ability to concentrate it. This could lead to a condition called diabetes insipidus, where the urine is not concentrated properly, and excessive urination and thirst occur as a result.