The purpose of this study was to investigate the effect of the volume of consumed water on sweating response and plasma levels of arginine vasopressin, epinephrine and norepinephrine in the first few minutes of water drinking. Materials and Methods: After 4-h water deprivation, six healthy teakwondo champion were exposed to heat and performed mild exercise under an ambient temperature (2 hours, 38- 40°C, relative humidity<30%). Subjects were dehydrated by sweating. They were then allowed to drink water with volumes of 1, 3, and 5 ml/kg of body weight using three separate protocols. Sweat rate was measured by amount of sweat collected from the forehead area in grams during 3 minute periods before and after drinking. Blood samples were drawn before heat exposure, before drinking and then every 3 minutes up to the 15th minute after drinking. Results: Dehydration increased mean serum sodium (p<0.001). Sweating increased markedly just after the onset of drinking (p<0.01) and was greater when consumed water was 5ml/kg of body weight. The more the water volume consumed, the greater was the reduction in plasma arginine vasopressin 3 minutes after drinking. The reverse was true for plasma norepinephrine (p<0.01), whereas plasma epinephrine was essentially unchanged by drinking. Conclusion: These data suggest that oropharyngeal sensors that interfere with the activation of sweating response can also manipulate it by consumed water volume. Moreover, the amount of water received affected plasma arginine vasopressin and norepinephrine but not plasma epinephrine which suggests a drinking stimulated neural mechanism.
