title: Dehydration in stressed ruminants may be the result of a cortisol-induced diuresis.
abstract: The effect on water and electrolyte balance of stress, simulated by intravenous infusion of cortisol, was studied using 24 18-mo-old Merino wethers (37.0 +/- 0.94 kg mean body weight [BW]) over 72 h. The sheep were allocated to one of four groups: 1) no water/no cortisol (n = 6); 2) water/no cortisol (n = 4); 3) no water/cortisol (n = 6); and 4) water/cortisol (n = 4). Animals allocated to the two cortisol groups were given 0.1 mg x kg BW(-1) x h(-1) of hydrocortisone suspended in isotonic saline to simulate stress for the duration of the experiment. Total body water, plasma cortisol, osmolality and electrolytes, and urine electrolytes were determined at 24-h intervals for 72 h. In the presence of cortisol, total body water was maintained in the face of a water deprivation insult for 72 h. Water deprivation alone did not induce elevated plasma concentrations of cortisol, in spite of a 13% loss of total body water between 48 and 72 h. Infusion of cortisol was found to increase urine output (P = 0.003) and decrease total urinary sodium output (P = 0.032), but had no effect on plasma electrolyte levels or water intake. Water deprivation was found to increase plasma sodium concentrations (P = 0.037). These results indicate that sheep given cortisol to simulate stress suffer from a loss of body water in excess of that associated with a loss of electrolytes, and support the hypothesis that elevated physiological concentrations of cortisol induce a diuresis in ruminants that contributes to dehydration.
authors.affiliation: Australian Institute of Tropical Veterinary and Animal Science, School of Biomedical Sciences, James Cook University, Townsville 4811, Australia.
authors.forename: A J
authors.initials: AJ
authors.lastname: Parker
authors.forename: G P
authors.initials: GP
authors.lastname: Hamlin
authors.forename: C J
authors.initials: CJ
authors.lastname: Coleman
authors.forename: L A
authors.initials: LA
authors.lastname: Fitzpatrick
mesh_terms: D000818:Animals; D001834:Body Water / Q000378:metabolism; D003681:Dehydration / Q000209:etiology / Q000662:veterinary*; D004231:Diuresis / Q000187:drug effects*; D004573:Electrolytes / Q000097:blood / Q000378:metabolism / Q000652:urine; D006854:Hydrocortisone / Q000097:blood* / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D009994:Osmolar Concentration; D011897:Random Allocation; D012756:Sheep; D012757:Sheep Diseases / Q000209:etiology* / Q000503:physiopathology; D013312:Stress, Physiological / Q000150:complications / Q000503:physiopathology / Q000662:veterinary*; D014882:Water-Electrolyte Balance / Q000187:drug effects
chemical_list: D004573:Electrolytes; D006854:Hydrocortisone