Title Adverse effects of dietary and furosemide-induc-Pd 9b deo 0 ethicnn 0 on thermoregulation in rats

,-In this study the diuretic furosemide was used in combination with dietary sodium (Na) restriction, to produce varying degrees of circulatory hyponatremia to quantify the effects of moderate to severe Na-depletion on heat tolerance in a validated, heat stressed rat model. Male Sprague-Dawley rats (500 g) were subjected to a Na-depletion regimen as follows: group I (control) had free access to a normal diet and tap water; group II consumed the normal diet and tap water but was treated with the diuretic furosemide (10 mg/kg/day, ip); group III had free access to a Na-free diet and deionized drinking water; group IV consumed the same Na-free diet and electrolyte-free water but was also treated with furosemide. Both the dietary and drug manipulations effected significant (p<.05) negative Na and water baldnce aiLd hyponatremia in the experimental groups. Group IV consistently exhibited the greatest decrements. Following four days of depletion all four groups were acutely exposed to a 42*C environmental heat stress during which time rectal temperature increased. The time required for rectal temperature to reach 42.61C was significantly (p<.05) decreased to 176 ± 14 and 181 ± 8 minutes in groups II and III, respectively, from a control time of 242 ± 8 min in group I; tolerance for group IV was decreased even more to 111 ± 11 minutes. It is concluded that in the sedentary rat Na deprivation and diuretic treatment can elicit a 25-50% reduction in heat tolerance which is partially due to electrolyte depletion and hypohydration. These data suggest that during environmental heat stress uncompensated negative Na balance may predispose an individual to heat illnesses.