Salt loading test in a population adapted to moderately high altitude living (3,000 m)

The sodium excretory capacity of normal subjects acutely mobilized from sea level to moderately high altitude was compared to native subjects adapted to high altitude living (3,000 meters). This study was conducted in order to provide insights into hormonal adaptations associated with acute mobilization to a hypoxemic environment and to try to determine how these variables could influence the renal handling of a salt load. A standard amount of 5% NaCl solution at a volume of 100 ml/m2 BSA was infused over a 30-min period to all subjects. Urine collections were obtained periodically over the next 3 h. Subjects adapted to moderately high altitude living were able to excrete a salt load faster than unadapted subjects (57.1 vs. 32.9 mmol.m-2.h-1, respectively). No change in plasma atrial natriuretic factor (ANF) concentration in either group of subjects was observed during the salt administration period. Adapted individuals had significantly higher baseline levels of antidiuretic hormone (ADH). The high altitude natives enhanced excretory response to a salt load was not explained by any observed hormonal changes and their lack of increased ADH release to serum osmolar changes was unexplained.