SALT EXCRETORY CAPACITY IN ADAPTED TO MODERATE HIGH-ALTITUDE LIVING AFTER ACUTE MOBILIZATION TO SEA-LEVEL

The sodium excretory capacity of six normal subjects born and raised a t moderately high altitude (2600 m) was evaluated at high altitude (HA ), and after acute mobilization to sea level (SL). The ability of thes e individuals to respond to an acute salt load was evaluated by infusi ng a volume of 100 ml . m(-2) body surface area (BSA) of 5% sodium chl oride solution over a 30-min time period in both experimental conditio ns. HA natives were able to excrete a significantly greater salt load at HA than at SL (41.8% vs. 31.6%, respectively, p < 0.05) in 3 h. No changes in plasma atrial natriuretic factor (ANF) concentration were f ound in either experimental condition. Despite an increase in serum os molality, no vasopressin (AVP) response was noted either at HA or SL. No correlation between serum AVP levels and urine c-AMP concentrations was found. The enhanced excretory response to a salt load at HA was n ot explained by the measured hormonal changes. The lack of AVP respons e to increased serum osmolality, both at HA and SL, in high altitude a dapted subjects is presently unexplainable.