Biobehavioral determinants of evaporative water loss in the rat

Abstract

R. C. Ritter and A. N. Epstein (1974, Behavioral Biology , 11 , 581–585) reported that grooming water loss constituted 30% of the total evaporative water loss of the rat during a 24-hr test in the absence of food and water. They suggested that dehydrated rats may conserve water behaviorally by grooming less, predicting that grooming water loss should increase with ingestants available. The two experiments reported here tested the hypothesis and extended our overall understanding of the behavioral and physiological determinants of evaporative water loss. In the first experiment the total evaporative water loss of Sprague—Dawley rats ( Rattus norvegicus ) was measured over 23 hr using the technique of F. R. Hainsworth (1967 , American Journal of Physiology , 212, 1288–1292). The magnitude of grooming water loss was determined by subtracting the evaporative water loss of surgically desalivate rats (equivalent to insensible water loss) from that of intact controls. During testing, rats had either food and water, only water, or neither food nor water available. The second experiment shared the design of the first and quantified grooming and general activity (the main behavioral determinants of grooming and insensible water losses, respectively) using the apparatus of Beagley and Gallistel (1971 , Physiology and Behavior , 7, 273–276). Grooming water loss was found to constitute 7–8% of total daily evaporative water loss. Although dehydration reduced grooming behavior slightly, grooming water loss was not detectably altered; suggesting that rats do not groom less in order to conserve water when in a state of water need. Deprivation of food or of both food and water reduced insensible water loss by 35–40%. Since general activity was unaffected by the availability of ingestants, this latter effect appears to be physiologically, rather than behaviorally, mediated.