Prolonged hypobaric hypoxemia attenuates vasopressin secretion and renal response to osmostimulation in men

Effects of hypobaric hypoxemia on endocrine and renal parameters of body fluid homeostasis were investigated in eight normal men during a sojourn of 8 days at an altitude of 4,559 m. Endocrine and renal responses to an osmotic stimulus (5% hypertonic saline, 3.6 ml/kg over 1 h) were investigated at sea level and on day 6 at altitude. Several days of hypobaric hypoxemia reduced body weight (−2.1 ± 0.4 kg), increased plasma osmolality (+5.3 ± 1.4 mosmol/kgH2O), elevated blood pressure (+12 ± 1 mmHg), reduced creatinine clearance (122 ± 6 to 96 ± 10 ml/min), inhibited the renin system (19.5 ± 2.0 to 10.9 ± 0.9 mU/l) and plasma vasopressin (1.14 ± 0.16 to 0.38 ± 0.06 pg/ml), and doubled circulating levels of norepinephrine (103 ± 16 to 191 ± 35 pg/ml) and endothelin-1 (3.0 ± 0.2 to 6.3 ± 0.6 pg/ml), whereas urodilatin excretion rate decreased from day 2 (all changes P < 0.05 compared with sea level). Plasma arginine vasopressin response and the antidiuretic response to hypertonic saline loading were unchanged...