Reduced thirst in old, thermally dehydrated rats

• Published in: Physiology & behavior Vol. 81; no. 4; pp. 569 - 576
• Main Authors: Whyte, Douglas G, Thunhorst, Robert L, Johnson, Alan Kim
• Format: Journal Article
• Language: English
• Published: Cambridge Elsevier Inc 01.06.2004; New York, NY Elsevier
• Subjects: Aging; Aging - physiology; Analysis of Variance; Animals; Biological and medical sciences; Body Temperature Regulation - physiology; Dehydration - physiopathology; Drinking; Drinking - physiology; Fundamental and applied biological sciences. Psychology; Heat exposure; Hyperthermia; Hyperthermia, Induced; Metabolisms and neurohumoral controls; Random Allocation; Rats; Rehydration; Thermal dehydration; Thirst; Thirst - physiology; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Water and mineral metabolism. Osmoregulation. Acidobasic balance; Heat exposure; Aging; Rehydration; Thermal dehydration; Drinking; Thirst; Hyperthermia; Hydroelectrolytic balance disorder; Feeding behavior; Osmolarity; Rodentia; Rattus norvegicus; Environmental factor; Dehydration; Vertebrata; Heat; Mammalia; Developmental stage; Age; Comparative study; Room temperature
• ISSN: 0031-9384; 1873-507X
• DOI: 10.1016/j.physbeh.2004.02.030

Water intake and blood parameters of young (7-month) and old (23-month) male Brown Norway rats were assessed following a period of thermal dehydration. Rats of both ages were randomly assigned to one of three groups: (1) Unheated-blood sample, (2) Heated-blood sample, and (3) Heated-water intake. The colonic temperature of heated rats was raised at the rate of 0.05 °C/min for 1 h using an infrared heat lamp. Water intake was then measured over the following 2 h. The heating protocol resulted in a similar level of dehydration in both young and old rats; however, plasma osmolality and sodium concentration increased to a significant extent only in the young rats. Old rats drank significantly less water at all time points during the 2 h following the heat stress. While neither group replaced the water lost as a result of the thermal dehydration, the young rats did rehydrate to a greater extent. These results suggest that the diminished level of rehydration in aged rats, following a thermal dehydration, is due to an attenuated rise in plasma osmolality.