Hormonal changes with lower body negative pressure on the 6th day in microgravity in one cosmonaut

We measured volume regulating and stress hormones (AVP, aldosterone, ANP, c-GMP, angiotensin II, PRA, epinephrine, norepinephrine, ACTH, cortisol) in venous blood twice during a lower body negative pressure (LBNP) maneuver in one cosmonaut (31 years, 75 kg, 180 cm) preflight (supine), inflight (6th d in orbit), and on the 4th d (supine) after a 10-d flight. Antecubital blood was taken at the beginning (3 min: "a") and after ceasing (2 min: "b") 40 min LBNP (-15/-30/-35 mm Hg for 15/15/10 min). At the beginning of LBNP, no big changes of resting hormone levels are to be expected. Comparison of "a" values: Inflight, there was a 4-5-fold increase in vasopressin and epinephrine, a slight increase in aldosterone, ANP, norepinephrine, cortisol and ACTH, and a decrease in PRA levels. Postflight, vasopressin was almost as much increased as inflight, and aldosterone and ANP levels were higher than pre- or inflight. PRA, epinephrine, norepinephrine, and cortisol were moderately increased, whereas ACTH and angiotensin II were diminished. Comparison of "b" to "a" values (2 min after LBNP to 3 min intra-LBNP): Preflight, ANP, PRA, and epinephrine rose more than 100%. The inflight response was higher for aldosterone but lower for all other volume active hormones. Postflight, the increase in PRA was pronounced, whereas little change occurred in other hormones. Cortisol and ACTH fell similarly during LBNP under all conditions. In summary, the data provide evidence that not only the endocrine status but also the neuroendocrine responsiveness to stimulation; i.e., the hormone response during cardiovascular load, are altered by the stay in microgravity and readaptation to normal conditions.