Effects of high altitude and water deprivation on arginine vasopressin release in men

High-altitude exposure changes the distribution of body water and electrolytes. Arginine vasopressin (AVP) may influence these alterations. The purpose of this study was to examine the effect of a 24-h water deprivation trial (WDT) on AVP release after differing altitude exposures. Seven healthy males (age 22 ± 1 yr, height 176 ± 2 cm, mass 75.3 ± 1.8 kg) completed three WDTs: at sea level (SL), after acute altitude exposure (2 days) to 4,300 m (AA), and after prolonged altitude exposure (20 days) to 4,300 m (PA). Body mass, standing and supine blood pressures, plasma osmolality (P_osm), and plasma AVP (P_AVP) were measured at 0, 12, 16, and 24 h of each WDT. Urine volume was measured at each void throughout testing. Baseline P_osm increased from SL to altitude (SL 291.7 ± 0.8 mosmol/kgH₂O, AA 299.6 ± 2.2 mosmol/kgH₂O, PA 302. 3 ± 1.5 mosmol/kgH20, P < 0.05); however, baseline P_AVP measurements were similar. Despite similar P_osm values, the maximal P_AvP response during the WDT (at 16 h) was greater at altitude than at SL (SL 1.7 ± 0.5 pg/ml, AA 6.4 ± 0.7 pg/ml, PA 8.7 ± 0. 9 pg/ml, P < 0.05). In conclusion, hypoxia appeared to alter AVP regulation by raising the osmotic threshold and increasing AVP responsiveness above that threshold.