Plasma electrolytes in relation to altitude tolerance in rats.

Plasma concentration of Na+, K+ and Cl- ions did not change significantly whereas that of HCO3- dropped to one-third of its initial value in rats during their 15 min of gasping at a simulated altitude of 10,000 m at 33 degrees C, which was their survival threshold. Administration of methamphetamine (2 mg/kg), imipramine (2 mg/kg) and adrenaline (7 mg/kg) i.p. were ineffective in prolonging the survival time of rats, whereas acetazolamide (40 mg/kg), furosemide (2 mg/kg) and caffeine citrate (10 mg/kg) significantly increased their survival under hypoxia, (p less than 0.001, less than 0.01, and less than 0.05, respectively).