Naloxone blocks exercise-stimulated water intake in the rat

To examine whether opiate receptors modulate exercise-induced water intake, we measured water intake during four consecutive hours after a one-hour swim stress in male, Sprague-Dawley rats. Increased cumulative water intake was found four hours following exercise and this response was naloxone-reversible (P = 0.06). Suppression of water intake in the naloxone-treated, exercised group was most marked in the first two hours after exercise (P less than 0.05). Non-exercised rats consumed water at a constant, linear rate (P less than 0.05) whether treated with naloxone or saline. These results indicate an endogenous opioid role in regulating exercise-induced water intake in the rat, but do not delineate whether this role reflects a non-specific stress behavior or specific physiological processes related to thirst.