Evaporative water loss from rats in the heat.

1968.-In rats in the heat water lost through saliva is the major component of evaporative water loss. Total evaporative water loss was measured from normal and desalivated rats and salivary evaporative water loss was then estimated as the difference in evaporation between normal and desalivated rats. Above 32 C the salivary evaporation gradually increased up to 44 C which was the highest experimental temperature. At 44 C males and females evaporated similar amounts, but below 44 C males evaporated more salivary water. In desalivated rats evaporative water loss was much smaller, but it likewise increased with ambient temperature. Comparisons are made with other rodents, and water losses are related to other responses reported for rats under heat stress. M ANY MAMMALS do not sweat or pant but increase heat loss through evaporation by spreading saliva on their body surfaces. Use of saliva for cooling has been observed in a variety of species (4, 7-10, 12, 13) and has been shown to be of vital importance for the control of hyper-thermia in the Virginia opossum (9) and the rat (7). The present report is concerned with the measurement of water loss through saliva spreading as a function of temperature. In addition, the water losses of laboratory rats are compared to losses from other rodents and are related to previously described responses of rats to heat stress (7). METHODS Animals. Five male (320-410 g) and five female (290-370 g) Sprague-Dawley albino rats were completely desalivated by ligation of the parotid ducts and surgical removal of the submaxillary-sublingual glands (16). Successful removal of saliva was indicated by the ani-mal's adoption of a prandial style of drinking with con-comitant increases in daily water intake (5, 16). Six males and five females served as unoperated controls. Animals were housed individually at room temperature (25 C) and each was given continuous access to Purina food pellets and distilled water. Evaporative water loss. Evaporative water loss was measured in an open-flow system (Fig. 1). Compressed air was passed through the system at a constant rate of 4 liters/min. Moisture in the air was removed by passage through tubes (A) of Drierite dessiccant (anhydrous calcium sulfate). For temperature equilibration the air was then passed through copper coils (B) located within the incubator. After passage through a flowmeter (C) (Fisher-Porter), the air was introduced into the bottom of a modified l-gal tin can (D) containing the animal. This chamber …