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Effects of High Altitude and Hypophagia on Mineral Metabolism of Rats¹

Letterman Army Institute of Research, Presidio of San Francisco, California. 94129

Electrolyte excretion and balance were compared in meal-eating, ad libitum-fed rats maintained in Denver (1,600 m) and on Pikes Peak (4,300 m) and in meal-eating rats maintained in Denver but pair-fed to the Pikes Peak animals. Most of the changes in excretion and balance at Pikes Peak were attributable to hypophagia. At both elevations, equivalent decrements in mineral intake led to nearly equivalent decrements in mineral excretion. Comparisons of the Pikes Peak and Denver pair-fed animals, however, revealed certain changes that were unique to high altitude. These included a marked and sustained reduction in ammonia excretion over the 13-day period of exposure. The higher elevation also produced an enhanced sodium excretion on day 1 of exposure and a reduced sodium blance over the first 6 days. Potassium balance showed no changes unique to high altitude during the first 6 days on Pikes Peak but was significantly reduced during week 2 of exposure. The urinary sodium:potassium ratio was elevated during the first 4 days at 4,300 m, but this effect was attributable to altitude on day 1 only. Enhanced calcium and magnesium excretions, relative to those observed in the pair-fed rats, were observed over the middle and latter portions of the exposure period. The balance of these two minerals showed no altitude-dependent effects. Chloride and phosphate excretions showed an altitude-dependent reduction during day 1 and week 1 of exposure, respectively. These changes were associated with more positive balances. It is concluded that the altitude-dependent effects on mineral metabolism are largely, if not entirely, attributable to hypocapnia and associated alkalosis.

KEY WORDS: • altitude • hypophagia • mineral metabolism

¹ The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. In conducting the research described in this report, the investigators adhered to the Guide for Laboratory Animal Facilities and Care, as promulgated by the Committee on the Guide for Laboratory Animal Facilities and Care of the Institute of Laboratory Animal Resources, National Academy of Sciences-National Research Council.

² Present address: Smith Kline & French Laboratories, West Chester, Penn. 19380.

³ Present address: Chemistry Department. University of Arkansas, Fayetteville, Ark. 72701.

Manuscript received 17 September 1973.

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