Abstract
Armstrong 1 has reported that humans subjected daily to a simulated altitude of 12,000 feet in a low-pressure chamber excreted on the average 100% more urine than at sea level. An even more marked polyuria has been invariably observed in white rats maintained at a level of 15,000 feet for periods of 3 hr; 2 though in the case of anesthetized dogs breathing low-oxygen gas mixtures, Van Liere et al. 3 and Toth 4 have observed oliguria to occur more frequently than polyuria. The present experiments were undertaken to determine whether, on repeated daily exposure to low barometric pressure, this polyuria would be maintained over a long period of time, or whether acclimitization and consequent normal urine output would result.
Healthy male white rats, weighing from 150 to 200 g, were maintained on a stock diet of Purina Dog Chow and liberal amounts of greens, with water allowed ad libitum. Food, but not water, was removed from the 12 animals comprising an experimental group 12 hr before the start of an experiment, and the following morning the rats were placed in wire-mesh metabolism cages set over graduated cylinders in a specially-designed low-pressure chamber (capacity 500 liters). The chamber was evacuated to a pressure of 428.8 mm Hg (15,000 feet altitude equivalent) and maintained at this level for 3 hr, at the end of which time air was admitted; the animals removed; and the urine volume read and recorded. The temperature of the chamber was not precisely controlled; in each experiment, however, a thermometer inserted through the wall was observed to rise, in the course of the 3-hr period, from an initial 23° to a final 28°C.
A group of 36 animals, placed in metabolism cages for 3 hr at room pressure, excreted an average of 0.4 cc urine per 100 g body weight.
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