Acclimatization Response of Rats to Discontinuous Exposures to Simulated High Altitudes

Abstract

Male rats were exposed discontinuously for 4 hrs. to 18,000 and 25,000 feet simulated altitude to study the rate and degree of acclimatization which could be induced by various exposure regimes. Hematocrit values showed that polycythemia developed in proportion to the frequency, intensity, and duration of the hypoxia. The upper limit of the hematocrit was approx. 80 with the greatest degree of stress. Relatively high hematocrit values (55-75) could be maintained by exposures at intervals of 2 or 3 days, but not by exposures at greater intervals. After max. hematocrit values were reached for each exposure regime, they could be maintained relatively constant for many mos. The rate of occurrence of testis damage, the nature of the reproductive performance, and the rate of recovery of reproductive function in rats exposed for 4-hr. periods at 25,000 feet were studied. The 1st evidence of damage to the testis was detected after only 3 daily 4 hr. exposures. Sterility developed when rats were exposed repeatedly up to once per week, but not when exposures were admd. at greater intervals. After sterility developed prolonged removal from high altitude was necessary to restore fertility. Cardiac hypertrophy, cardiac valvular vegetations, and widespread hemosiderosis of the kidney, spleen, and lungs were often found in rats exposed to 25,000 feet 80 or more times at intervals of from 1-3 days. The incidence and severity of these changes increased as the exposures were continued and decreased with rest. However, some of the changes were noted 80 days after the last exposure to altitude.