Thirst perception and drinking in euhydrate and dehydrate human subjects

Studies on how the body senses the need to correct extracellular and intracellular volumes and ionic
concentration changes is relatively scanty. The present studies were designed to determine the effect of oral distilled
water (DW) and saline loads, gargling with DW and DW preload on thirst perception (TP) and drinking in euhydrate
and dehydrated subjects. The subjects were healthy male volunteers between the ages of 17 and 35 years. Group A
subjects were given DW or various concentrations of sodium chloride (NaCl) orally. Subjects in groups B, C and D
were dehydrated for 18 hours before the experiment. Group B gargled 500ml of DW in divided volume of 50ml at
five minutes interval over a period of 50 minutes. Group C gargled with DW and different concentrations of NaCl.
Group D were preloaded with four volumes of DW before ad libitum DW intake. TP was rated using the Visual
Analogue Scale. Results showed that in Group A, drinking DW reduced TP, suggesting that baseline TP in normal
euhydrate subjects is slightly elevated. Drinking DW reduced TP more than drinking NaCl solutions. Gargling
resulted in a gradual fall in TP. The decrease in TP was statistically significant after 30 minutes of gargling.
Gargling with different concentrations of NaCl solutions resulted in significant reductions in TP in all the groups.
There was a significant decrease in TP in the group preloaded with 1000ml of distilled water at 5 minutes of
rehydration. At 20 minutes TP was abolished suggesting that approximately 1000ml of water was needed for the
rehydration. These results show that baseline TP in euhydrates is elevated and that TP increases in dehydrated
subjects. Gargling reduces TP, but did not abolish thirst. It is suggested that a fall in plasma osmolality due to
drinking may be responsible for abolishing thirst.