Which of the following conditions would result result in a decrease in the production of antidiuretic hormone?

Analyze the question: ADH (antidiuretic hormone, or vasopressin) is made in the hypothalamus and released by the posterior pituitary. We need the condition that lowers its production.

Concept: ADH controls water reabsorption in the kidney's collecting ducts and distal tubules.

• When the blood is too concentrated (high osmotic pressure, dehydration), osmoreceptors in the hypothalamus detect it and ADH production rises. More water is reabsorbed, so less, more concentrated urine is produced.
• When the blood is too dilute (low osmotic pressure, excess water), ADH production falls. Less water is reabsorbed, so large amounts of dilute urine are produced.

Evaluating the options:

• A. Abnormally high blood sugar: This raises the osmotic pressure of the blood, and glucose in the urine pulls water with it. The body is short of water, so ADH increases, not decreases.
• B. Drinking large quantities of water: This dilutes the blood and lowers its osmotic pressure. ADH secretion falls, the kidneys reabsorb less water, and dilute urine is excreted. This matches the question.
• C. Increase in osmotic pressure of blood: This is the direct trigger for more ADH release, the opposite of what we want.
• D. Strenuous exercise: Sweating causes water loss and a more concentrated blood, so ADH increases.

Answer: B

Exam tip: Remember "ADH = Anti-Diuresis Hormone", meaning it stops lots of urine. If you are dehydrated, ADH goes up. If you have taken in plenty of water, ADH goes down. For any such question, ask yourself: "Is the blood becoming more concentrated or more dilute?"