A 49-year-old man presents with dehydration, hypokalemia, and watery diarrhea. Which hormone would most likely control his condition?

• A. Aldosterone
• B. Cholecystokinin
• C. Gastric inhibitory polypeptide
• D. Vasoactive intestinal polypeptide

Answer: (D)

In the context of this case, the patient presents with dehydration, hypokalemia, and watery diarrhea, suggesting a condition related to excessive fluid loss and electrolyte imbalance. The hormone that would most likely control such a condition is vasoactive intestinal polypeptide (VIP).

VIP is a neuropeptide that has several important functions in the gastrointestinal tract, including the stimulation of intestinal fluid secretion and promoting motility. It is primarily involved in the regulation of water and electrolyte balance in the intestines. In cases of secretory diarrhea, VIP levels can be elevated, leading to increased intestinal fluid secretion, which may contribute to the patient's symptoms of watery diarrhea.

In this scenario, if VIP is overproduced or if there's an underlying condition such as VIPoma (a rare type of tumor that secretes large amounts of VIP), it would lead to a significant increase in intestinal secretions, resulting in diarrhea and dehydration, as well as hypokalemia due to the loss of potassium in the stool.

While aldosterone, cholecystokinin, and gastric inhibitory polypeptide play roles in fluid and electrolyte balance or digestion, they are not the primary hormones responsible for the severe secretory diarrhea that results in the symptoms demonstrated by this patient. Thus,