Osmotic thirst suppression in dogs exposed to low ambient temperature.

Body temperature, urine output, osmotic and free water clearances, plasma osmolality, sodium and potassium concentrations, blood lactate level, osmotic thirst and central blood volume were measured in dogs exposed to cold (+1 to -8 degrees C) for 1-3 hours and compared to those obtained under control conditions at ambient temperatures (18-20 degrees C). In some additional experiments osmotic thirst threshold and arterial blood pressure during intravenous infusion of norepinephrine were also examined. Exposure to low ambient temperature caused an increase in the osmotic thirst threshold and rise in central blood volume. Transient increase in the urine output and free water clearance accompanied by a decrease in the urine osmolality were also observed. No changes were found in rectal temperature, plasma osmolality and plasma sodium concentration. Infusion of norepinephrine elevated the osmotic thirst threshold in a dose-dependent manner. It is concluded that the cold-induced suppression of osmotic thirst may result from the increased central blood volume. A possible involvement of the sympathetic nervous system in the thirst inhibition in low ambient temperature is also considered.