Permanent depression of plasma cGMP during long-term space flight

Area of Science:

• Cardiovascular Physiology
• Space Medicine
• Biomarker Research

Background:

• Spaceflight alters physiological systems, impacting fluid balance and cardiovascular regulation.
• Atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP) are key regulators of fluid and electrolyte homeostasis.
• Understanding these biomarkers' response to microgravity is crucial for astronaut health.

Purpose of the Study:

• To investigate plasma concentrations of cGMP and ANP during and after real and simulated space flight.
• To assess the impact of short- and long-duration space missions on these biomarkers.
• To evaluate the effects of head-down tilt bed rest as a simulation of weightlessness.

Main Methods:

• Blood samples were collected from two cosmonauts preflight, inflight, and postflight.
• Blood samples were collected from five subjects before, during, and after a 5-day head-down tilt bed rest simulation.
• Plasma cGMP and ANP levels were measured using established assays.

Main Results:

• Plasma cGMP levels decreased significantly in both cosmonauts during spaceflight.
• Long-duration spaceflight (438 days) led to a near-complete disappearance of plasma cGMP.
• Simulated weightlessness (head-down tilt bed rest) also resulted in a marked reduction in plasma cGMP.
• Cosmonaut 2 showed low inflight ANP, returning to baseline postflight.

Conclusions:

• Real and simulated weightlessness consistently lower plasma cGMP levels.
• Long-duration spaceflight causes a profound and prolonged reduction in plasma cGMP.
• These findings highlight the significant physiological adaptations occurring during spaceflight and bed rest.