Sympathoadrenal Activity in Humans During Spaceflight (Sympatho)
Research Area: Nervous and Vestibular Systems
Expedition(s): 5, 8, 11
Principal Investigator(s): ● Niels J. Christensen, University of Copenhagen,
Copenhagen, Denmark
RESEARCH OBJECTIVES
Sympathoadrenal Activity in Humans During Spaceflight (Sympatho) studies the influence of
microgravity on adrenal activity in the sympathetic nervous system, which has importance for
cardiovascular system regulation such as accelerating heart rate, constricting blood vessels, and
raising blood pressure in short-duration space explorers. Ground-based experiments have shown
that the sympathetic activity is decreased in response to displacement of the blood from the lower
part of the body to the heart-lung area after changing from the upright or sitting position to the
supine (lying on back) position. In space, sympathetic activity is expected to be decreased but
experiments have suggested that it actually increases during weightlessness. This is the core
element of the Sympatho experiment.
RESULTS
Long-term changes in sympathoadrenal activity were
measured through platelet norepinephrine and
epinephrine levels. Ten normal, healthy subjects were
studied before and during head-down bed rest (HDBR)
of 2 weeks duration, as well as during an ambulatory
study period of a similar length. Platelet norepinephrine
and epinephrine concentrations (preflight and
postflight) were studied in 5 cosmonauts who
participated in 3 different Soyuz missions to the
International Space Station (ISS). Due to the long half-life
of norepinephrine and epinephrine in platelets
(approximately 2 days), data obtained early after landing
would still reflect the microgravity state. Platelet
norepinephrine decreased markedly during HDBR.
During microgravity platelet norepinephrine and
epinephrine increased in 4 of the 5 cosmonauts. Platelet
norepinephrine and epinephrine concentrations
expressed in percentage of preflight and pre-HDBR values, respectively, were significantly
increased during microgravity as compared to HDBR. The increase in platelet norepinephrine and
epinephrine during microgravity is most likely due to an increase in sympathoadrenal activity. The
reason why sympathoadrenal activity does not decrease to low levels during microgravity as one
would expect remains to be resolved.
The exact interrelationship in microgravity between the increase in cardiac output, the
decrease in plasma volume and the increase in sympathoadrenal activity during spaceflight
remains to be clarified. Plasma volume decreases inflight, but this change is unlikely to explain
the increase in sympathetic nervous activity. There did not appear to be a pronounced early
Freezer Kriogem-03 for storage of blood
samples. ESA image.