Adverse effects of dietary and furosemide-induced sodium depletion on thermoregulation

In this study, the diuretic furosemide was used in combination with dietary sodium (Na) restriction to quantify the effects of moderate to severe Na depletion on heat tolerance in a validated model of heat stress in rats. Rats were subjected to an Na depletion regimen as follows: a control group (I, n = 17) had free access to a normal diet and tap water; group II (n = 20) consumed the same normal diet and tap water, but was treated with the diuretic furosemide at a dose of 10 mg.kg-1.d-1, ip; group III (n = 18) had free access to an Na-free diet and deionized drinking water; group IV (n = 21) consumed the same Na-free diet and electrolyte-free water, but was also treated with furosemide. Both the dietary and drug manipulations affected significant (p less than 0.05) negative electrolyte and water balances. Group IV consistently exhibited the greatest decrements. Following the 4-d depletion all four groups were acutely exposed to a 42 degrees C, 25-30% rh environmental heat stress during which time core body temperature increased. The time required for rectal temperature to reach 42.6 degrees C was significantly (p less than 0.05) decreased from a time of 242 +/- 8 min in the control group to 176 +/- 14, 181 +/- 8, and 111 +/- 11 min in groups II, III and IV, respectively. We concluded that Na deprivation and diuretic treatment can elicit a 25-50% reduction in heat tolerance due to electrolyte depletion and dehydration. These data confirm that during environmental heat stress uncompensated negative Na balance may predispose an individual to heat illnesses.