Central and peripheral noradrenergic responses to 14 days of spaceflight (SLS-2) or hindlimb suspension in rats.
BACKGROUND
The purposes of this work were to assess the influence of microgravity on the central and peripheral noradrenergic activity to reevaluate SLS-1 mission findings and to compare it with that of simulated microgravity in rats.


METHODS
The norepinephrine (NE) contents of the brainstem cell groups (A1, A2, A5, and A6) and organs (heart and kidneys) involved in blood pressure regulation were determined in rats after a 14-d spaceflight (SLS-2 with animals sacrificed 6 h after landing) and after a 14-d hindlimb suspension followed with 6 h of recovery.


RESULTS
After SLS-2 spaceflight, NE contents were not significantly different between flight and ground-based rats either in A1 (5.2 +/- 0.5 vs. 5.7 +/- 0.4 pmol/structure), rostral A2 (12.1 +/- 0.5 vs. 11.1 +/- 0.9 pmol/structure), caudal A2 (3.2 +/- 0.6 vs. 4.3 +/- 0.5 pmol/structure) and A5 (4.4 +/- 0.4 vs. 4.3 +/- 0.5 pmol/structure) nuclei or in cardiac atria (98.6 +/- 7.5 vs. 83.4 +/- 8.9 pmol.mg-1 protein), ventricles (38.3 +/- 2.2 vs. 44.1 +/- 2.8 pmol.mg-1 protein) and kidneys (13.4 +/- 0.8 vs. 17.7 +/- 1.5 pmol.mg-1 protein). NE content was unchanged in A6 nucleus after SLS-2 comparing with control rats (respectively 4.1 +/- 0.3 vs. 4.5 +/- 0.5 pmol/structure), while it was depleted after SLS-1 mission (2.9 +/- 0.3 vs. 8.8 +/- 0.7 pmol/structure, p < 0.001) probably in relation with the stressful conditions on return to Earth. Similarly, no alterations between suspended and control rats were noted in central and peripheral NE contents after 14 d of suspension and after 6 h of recovery, whereas NE turnover studies evidenced large changes in the activities on structures on suspension and on recovery.


CONCLUSIONS
These results suggest that only NE turnover determination will provide information about the role of the sympathetic system in the cardiovascular deconditioning. This raises the problem of the necessity to experiment inflight (injections, sacrifice) in order to avoid the recovery effects of the few hours following the landing.
Fagette
S
S
Laboratoire de Physiologie de l'Environnement (Groupement d'Intérêt Public Exercice), Faculté de Médecine Lyon-Grange Blanche, France.
Somody
L
L
Koubi
H
H
Fareh
J
J
Viso
M
M
Gharib
C
C
Gauquelin
G
G
D000818:Animals; D001933:Brain Stem / Q000737:chemistry; D007668:Kidney / Q000737:chemistry; D008297:Male; D009206:Myocardium / Q000737:chemistry; D009638:Norepinephrine / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D011941:Receptors, Adrenergic; D013026:Space Flight; D013564:Sympathetic Nervous System / Q000502:physiology*; D014893:Weightlessness
D011941:Receptors, Adrenergic; D009638:Norepinephrine