Effects of Exposure of Obese Rats to Simulated High Altitudes

¹ From the National Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

Osborne-Mendel rats became obese when fed a high fat diet for 6–15 months. Obese rats and stock-fed rats were exposed 6 1/2 hours a day, 5 days a week to 18,000 or 25,000 feet simulated altitude for from 4 to 6 months. Both groups of rats developed the same degree of polycythemia and had the same mortality rate. The obese rats lost more weight from altitude exposure and also showed a slightly higher incidence of cardiovalvular thickening and cardiac vegetations, particularly among those that died. The mean heart weight of unexposed obese rats was 50% greater than that of stock-fed rats; the heart weights of both groups increased about 70% following 191 days of exposure. In acute altitude tests at 33,500 feet simulated altitude, both Osborne-Mendel and Sprague-Dawley rats on the high-fat diet, irrespective of the degree of obesity, died within 86 minutes. Sixty per cent of the stock-fed rats survived for a longer period. Some of the heaviest Osborne-Mendel rats on the high-fat diet died within 3 minutes at this altitude. Preoxygenation prevented these early deaths, but neither preoxygenation nor a slow rate of ascent (500 ft/min) had any effect on the high mortality of rats on a high-fat diet exposed to altitude.