Influence of bed rest on plasma galanin and adrenomedullin at presyncope.
BACKGROUND
The role of hormones in reduced orthostatic tolerance following long-term immobilization remains uncertain. We have previously shown that plasma concentrations of adrenomedullin and galanin, two peptides with vasodepressor properties, rise significantly during orthostatic challenge. We tested the hypothesis that bedrest immobilization increases the rise in adrenomedullin and galanin during orthostatic challenge leading to presyncope.


METHODS
We measured baseline (supine), presyncope and recovery (10 min postpresyncope, supine) levels of adrenomedullin and galanin in 8 healthy men, before and after 21 days of -6° head-down bed rest (HDBR). Presyncope was elicited using a combined head-up tilt and graded lower body negative pressure protocol. Orthostatic tolerance was defined as the time taken from the commencement of head-up tilt to the development of presyncope.


RESULTS
Orthostatic tolerance time after HDBR reduced by 8·36 ± 5·39 min (P = 0·0032). HDBR increased plasma adrenomedullin concentration to orthostatic challenge (P = 0·0367). Compared to pre-HDBR, a significant rise in post-HDBR presyncopal (P < 0·001) and recovery adrenomedullin concentration (P < 0·01) was demonstrated. In contrast, we observed no change in pre- and post-HDBR galanin levels to orthostatic challenge.


CONCLUSIONS
Bedrest immobilization appears to affect adrenomedullin levels in that greater increases in adrenomedullin occur at presyncope following bedrest immobilization. Due to its peripheral vasculature hypotensive effect, the greater levels of adrenomedullin at presyncope following bedrest immobilization may have contributed to the reduced orthostatic capacity postbedrest.
Gravitational Physiology and Medicine research unit, Institute of Physiology, Medical University of Graz, Graz, Austria.|Centre of Human & Aerospace Physiological Sciences, King's College London, London, UK.
Daniel
D
O'Shea
Gravitational Physiology and Medicine research unit, Institute of Physiology, Medical University of Graz, Graz, Austria.
Helmut K
HK
Lackner
Gravitational Physiology and Medicine research unit, Institute of Physiology, Medical University of Graz, Graz, Austria.
Andreas
A
Rössler
Centre of Human & Aerospace Physiological Sciences, King's College London, London, UK.
David A
DA
Green
German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany.
Peter
P
Gauger
German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany.
Edwin
E
Mulder
Department of Biosciences, Biotechnologies and Biopharmaceutics University of Bari, Bari, Italy.
Grazia
G
Tamma
Gravitational Physiology and Medicine research unit, Institute of Physiology, Medical University of Graz, Graz, Austria.
Helmut
H
Hinghofer-Szalkay
Department of Biosciences, Biotechnologies and Biopharmaceutics University of Bari, Bari, Italy.
Giovanna
G
Valenti
Gravitational Physiology and Medicine research unit, Institute of Physiology, Medical University of Graz, Graz, Austria.
Nandu
N
Goswami
D053607:Adrenomedullin / Q000378:metabolism*; D000328:Adult; D001510:Bed Rest; D019004:Galanin / Q000378:metabolism*; D018475:Head-Down Tilt / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D008875:Middle Aged; D016683:Supine Position / Q000502:physiology; D013575:Syncope / Q000097:blood*; D018667:Tilt-Table Test; D055815:Young Adult
D053607:Adrenomedullin; D019004:Galanin
Head-up tilt; lower body negative pressure; orthostatic challenge; syncope