The Excretion of Catecholamines in Rats During Acute and Chronic Exposure to Altitude

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Abstract
The response of the sympathoadrenal medullary system in rats exposed to altitude has been assessed in terms of excretion of free noradrenaline (NA) and adrenaline (A) in the urine. Male Sprague–Dawley rats were either exposed acutely to simulated altitudes of 18 000 ft and 24 000 ft for 6 h or chronically to 18 000 ft for 5 weeks. Acutely exposed animals showed a considerable increase in the excretion of both catecholamines at 18 000 ft and 24 000 ft accompanied by a fall in body temperature. Acclimation to 18 000 ft by chronic exposure was achieved either by allowing the animals to reach the final altitude in stages during the 1st week, or by placing them directly at 18 000 ft. Body weight measurements confirmed that the second exposure condition was the more stressful. Although both groups showed an increase in NA excretion in the initial stages, only the second group exhibited an increase in A excretion. As the exposure continued, NA excretion returned towards sea level values. Preexposed animals maintained their body temperature at 18 000 ft and, when subsequently exposed to 24 000 ft for 6 h, did not excrete increased levels of NA or A. Increased activity of the sympathoadrenal medullary system appears to be involved only in the initial stages of acclimation to altitude.

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