If a marathon runner experiences significant dehydration leading to increased plasma osmolality, which consequence is most likely regarding the hypothalamic-pituitary axis?

💡 Explanation

Increased plasma osmolality stimulates osmoreceptors in the hypothalamus, triggering increased ADH (vasopressin) release from the posterior pituitary; because ADH enhances water reabsorption in the collecting ducts via aquaporin insertion, this mechanism helps reduce osmolality. Therefore, increased ADH and reabsorption are expected, rather than decreased ADH or sodium excretion.

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