Thermoregulatory responses to exercise in dehydrated dogs

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Abstract
Measurements of rectal temperature (Tre), water lost by evaporation (Eresp) and drooling, cardiac output (CO), and common carotid blood flow (CCBF) were made in dogs (mean hydrated wt 31.0 .+-. 1.5 kg) running for 1 h on a level treadmill at 7.5 km/h at an ambient temperature of 25.degree. C. Each animal was studied when it was hydrated ad libitum and when it had been dehydrated by removal of drinking water until 9-10% of the initial body weight had been lost. Dehydrated exercising animals had significantly higher Tre and lower rates of Eresp, CO, and CCBF. Tre and Eresp were measured in 7 animals. Average Tre during running was 39.11.degree. .+-. 0.10.degree. C in hydrated and 39.80.degree. .+-. 0.25.degree. C in dehydrated animals (P < 0.01). Average Eresp during running was 3.9 .+-. 0.3 g/min in hydrated animals and 2.3 .+-. 0.3 g/min in dehydrated animals (P < 0.01). Average CO during exercise, measured in 5 animals, was 11.1 .+-. 0.7 l/min in the hydrated state and 8.6 .+-. 0.5 l/min in the dehydrated state (P < 0.01). Unilateral CCBF during exercise, measured in 4 animals was 602 .+-. 40 ml/min in the hydrated state and 418 .+-. 22 ml/min in the dehydrated state (P < 0.01). Water lost by drooling in 7 exercising animals was 41.5 .+-. 11 g/h when they were hydrated and 0.6 .+-. 0.4 g/h when they were dehydrated. Dehydrated dogs doing mild exercise can save water by reducing Eresp and regulating body temperature above hydrated levels. The changes in thermoregulatory Eresp and CCBF and in CO in these dogs are similar to those which have been observed in dehydrated humans during exercise.

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