EXERCISE-ASSOCIATED HYPONATREMIA IN ALASKAN SLED DOGS - URINARY AND HORMONAL RESPONSES

Exercise-associated hyponatremia occurs in horses and humans, both spe cies that sweat, and in sled dogs, which do not sweat. To investigate the mechanism of exercise-associated hyponatremia in sled dogs, we mea sured water turnover, serum electrolyte concentrations and osmolality, plasma renal hormone concentrations, and urine composition of 12 fit Alaskan sled dogs before, during, and after a 490-km sled dog race (Ex group). Water turnover and serum electrolyte concentrations were meas ured in six similarly fit dogs that did not run (Sed group). Water tur nover was significantly larger (P < 0.001) in Ex [190 +/- 19 (SD) ml.k g(-1).day(-1)] than in Sed dogs (51 +/- 13 ml.kg(-1).day(-1)). There w ere significant (P < 0.001) decreases in serum sodium concentration (f rom 148.6 +/- 2.8 to 139.7 +/- 1.9 mmol/l) and osmolality (from 306 +/ - 9 to 296 +/- 5 mosmol/kgH(2)O) of Ex, but not Sed, dogs during the r ace. Plasma concentrations of arginine vasopressin decreased, whereas aldosterone and plasma renin activity increased significantly (P < 0.0 1) during the race. Urine osmolality was unchanged, whereas urine sodi um, potassium, and chloride concentrations decreased significantly (P < 0.05) and urine urea concentration increased (P = 0.06). These resul ts demonstrate increased water turnover associated with hyponatremia a nd renal sodium conservation with maintained high urine osmolality in exercising Alaskan sled dogs.