[70]

EFFECT OF AGE ON INACTIVITY IN RESPONSE TO INCREASED BODY WEIGHT INDUCED BY EXPOSURE TO HYPER-GRAVITY.   C.E. Wade¹, M.M. Moran¹, P.A. Fuller², T.M. Hobin-Higgins², L.A. Baer¹, T.P. Stein³ and C.A. Fuller². ¹Life Sciences Division, NASA Ames Research Center, Moffett Field, CA; ²Section of Neurobiology Physiology and Behavior, University of California, Davis, CA; and ³Department of Surgery, University of Medicine and Dentistry of NJ Stratford, NJ.

   We have previously demonstrated a reduction in activity related to the increase in body weight induced by centrifugation. The decrease in activity allows energy balance to be sustained. This work was conducted in young growing animals. With age there is a reduction in activity and energy expenditure. We hypothesized that mature animals would not adjust their activity and thus would have to increase energy intake to sustain balance. Young (Y; 1.5 mo.) and Mature (M; 8 mo.) male rats were divided into control (C) and hyper-gravity (2 g; HG) exposure groups (n= 8/group) and studied over 14 days. Body mass was reduced in both ages in response to HG: Y-C- 310 ± 4; Y-HG- 277 ± 3; M-C- 500 ± 9; M-HG- 438 ± 8 g. Energy balance and activity measurements were made over days 8-14. Energy intake and expenditure were greater in Y animals. Energy balance was 56± 16.7 and 10± 5.1 for Y and M.  There was no effect of HG. Activity was increased in the young rats compared to mature, 16 ± 0.5 vs. 7 ± 0.8 counts/min. In HG activity was reduced to 54 and 68% of control. The reduction in activity was inversely proportional to the increase in body weight (mass x g-level), 178% and 175%, to sustain energy balance. The reduction in activity was not effected by the age of the animals.

(Supported by NASA Grants: 121-10-30, 121-10-40, 121-10-50.)

[