Search NASA⌕ Search

Engineering topics

Philpott, D.

Publications and source records attributed to Philpott, D..

4 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Muscle mitochondrial density after exhaustive exercise in dogs - Prolonged restricted activity and retraining

The effect of exhaustive treadmill exercise on mitochondrial density (MD) and ultrastructural changes in quadriceps femoris muscle was studied in 7 normal, healthy, male mongrel dogs before and after restricted activity (RA) and following a subsequent 2-month exercise retraining period. Mean time to exhaustion in the 2-month group decreased from 177 +/- 11 min before to 90 +/- 16 min after RA; retraining increased tolerance to 219 +/- 36 min above the pre-RA and 143 percent above the post-RA time. Post-RA exhaustion time in the 5-months group was 25 and 45 min. Muscle samples taken after RA showed abnormalities indicative of degeneration, which were reversed by retraining. Resting MD decreased from a control level of 27.8 percent to 14.7 percent and 16.3 percent, and was restored to 27.1 percent after retraining. Exhaustive exercise caused an increase in MD under control conditions and after RA, but not following retraining. Disruption of mitochondria after exercise was evident after 5-month confinement. Factors causing mitochondrial changes and eventually their disruption during exercise after restricted activity are not related as much to the state of fatigue as to the pre-exercise quality of the muscle modified by disease or training.

Nazar, K.↗
NASA NTRS1991

Muscle ultrastructural changes from exhaustive exercise performed after prolonged restricted activity and retraining in dogs

The effect of exhaustive treadmill exercise on ultrastructural changes in the quadriceps femoris muscle was studied in 7 normal, healthy dogs, before and after restricted activity (RA), and following a subsequent 2 month treadmill exercise retraining period for the 5 mo group. Mean time to exhaustion in the 2 mo group decreased from 177 + or - 22 min before to 90 + or - 32 min after RA. Retraining increased tolerance to 219 + or - 73 min; 24 pct. above the before RA and 143 pct. above the after RA time. After RA exhaustion time in the 5 mo group was 25 and 45 min. Before RA, pre-exercise muscle structure was normal and post exercise there was only slight swelling of mitochondria. After RA, pre-exercise, numerous glycogen granules and lipid droplets appeared in the muscle fibers, mitochondria were smaller, and sarcoplasmic reticulum channels widened; post exercise these changes were accentuated and some areas were devoid of glycogen, and there was fiber degradation. After 5 mo RA pre-exercise there were more pronounced changes; mitochondria were very small and dense, there were many lipid droplets, myofibrils were often separated, and the fibers appeared edematous and degenerating; post exercise the sarcoplasmic reticulum was swollen, no glycogen was present, and there was marked swelling and deformation of mitochondria. After retraining, both pre-exercise and post exercise there was still evidence of fiber degeneration. Thus, susceptibility of active skeletal muscle structures and subcellular elements, e.g., mitochondria, to the action of damaging factors occurring during exhaustive exercise is enhanced considerably by prolonged disuse.

Nazar, K.↗
NASA NTRS1978

Effects of Radiation on Rat Retina after 18 days of Space Flight

Although cumulative effects an retina from low-dose radiation during prolonged spaceflight are not known, ary impairment of vision could set limits for spaceflight duration. Cosmic rays are now considered to be the cause of the "light flashes" seen during spaceflight by activating retina cells as they pass through the photoreceptors. Previous studies have also shown retinal cellular alterations and cell necrosis from high-energy, particle (HZE) radiation. Ten rats, 5 centrifuged during flight (FC) to simulate gravity and 5 in-flight stationary (FS) experiencing hypogravity, orbited Earth for 18.5 days on Cosmos 936. The animals were sacrificed 25 days post-recovery and the eyes flown to Ames Res. Ctr. The pattern of cell necrosis in the retinas from the FC group showed the same response to radiation as the FS. This would indicate that hypogravity was not a factor in the observed results. Also the cellular response in the retinas exposed in the Berkeley accelerator again matched both the FC and FS eyes. Thus all three conditions provide comparable changes and indicate HZE particles as the possible cause of the cellular alterations, channels, and breakdown.

Philpott, D.↗