Endocrine responses in long-duration manned space flight

Area of Science:

• Space physiology
• Endocrinology
• Biochemistry

Background:

• Space flight imposes unique stresses including weightlessness and confinement.
• Assessing physiological adaptation to space is crucial for crew health and performance.
• Endocrine and fluid balance changes are key indicators of adaptation.

Purpose of the Study:

• To evaluate biochemical adaptation to space flight.
• To identify hormonal, fluid, and electrolyte changes in crew members.
• To understand the physiological cost of maintaining performance in space.

Main Methods:

• Bioassay of body fluids (blood and urine).
• Measurement of hormonal parameters (aldosterone, vasopressin, catecholamines, cortisol).
• Correlation of fluid and electrolyte balance with weight loss and hormonal changes.

Main Results:

• Consistent patterns observed: body weight changes, increased plasma renin activity, elevated urinary catecholamines, antidiuretic hormone (ADH), aldosterone, and cortisol.
• Plasma cortisol decreased initially post-flight, then increased in 24-hour urine samples.
• Changes indicate a shift in fluid volume regulation, leading to increased renin and secondary aldosteronism.

Conclusions:

• Space flight induces significant fluid and electrolyte shifts, interpreted as volume expansion leading to diuresis.
• Adaptation to null-gravity involves compensatory hormonal mechanisms (renin-aldosterone system).
• While adapted, crew members may experience reduced functional reserve due to physiological costs of adaptation.