Biomedical subjects

T J Walters

Publications and source records attributed to T J Walters.

25 records · Page 2Linked to original sources

PubMed1991

Influence of electrical stimulation on a fast-twitch muscle in aging rats.

Recently we observed that the flexor digitorum longus muscle of the Fischer 344 rat, which is comprised primarily of type IIb muscle, does not change in size, fiber type, or physiological characteristics during senescence [Am. J. Physiol. 258 (Cell Physiol. 27): C1031-C1035, 1990]. This muscle was utilized to determine whether a predominantly fast-twitch glycolytic muscle would respond to tonic electrical stimulation (ES) with the same degree of fiber-type transformation in aging and young rats. The extent of transformation was quantified by measuring the contractile and metabolic properties, as well as the fiber-type composition, of the flexor digitorum longus muscle after ES (10 Hz, 8 h/day) imposed on the tibial nerve for periods of 0-90 days in young adult (YG; 6-8 mo), middle-aged (MA; 16-18 mo), and senescent (SN; 26-28 mo) male Fischer 344 rats. Although ES induced a IIb-to-IIa fiber-type shift in all groups, in the SN rats the shift was significantly less pronounced at the intermediate time points and remained incomplete after 90 days, compared with YG and MA rats. ES resulted in a reduction in tetanic tension (Po), which in the YG and MA rats was due to a reduction in muscle cross-sectional area. In the SN rats the reduced Po was due to a combined loss of cross-sectional area and specific tension (Po, N/cm2). Contraction and half-relaxation times were largely unaffected by ES, and maximal velocity of unloaded shortening declined throughout ES in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1990

Aging does not affect contractile properties of type IIb FDL muscle in Fischer 344 rats.

The purpose of this study was to examine the influence of aging on the contractile, metabolic, and histochemical properties of the predominantly fast-twitch flexor digitorum longus muscle (FDL) in the Fischer 344 (F344) rat strain. Contractile measurements were made in situ by stimulating the motoneuron while the animals were under pentobarbital sodium anesthesia. Fiber-type composition, capillarity, aerobic capacity, and myosin light chain composition were also examined. The results of this investigation were striking in that there was no alteration in any parameter measured. Collectively, these results suggest that aging does not induce a functional alteration in the neuromuscular relationship in the predominantly fast-twitch FDL of F344 rats, and consequently, there is no loss of functional capacity of the muscle. This study demonstrates that alteration in predominantly fast-twitch muscle is not a universal phenomenon and that care must be taken when generalizing about the influence of aging on skeletal muscle. Some of the conflicting results regarding the influence of aging on predominantly fast-twitch muscle in rodents may be either strain or muscle specific.

Aging↗

PubMed1988

Determinants of endurance in well-trained cyclists.

Fourteen competitive cyclists who possessed a similar maximum O2 consumption (VO2 max; range, 4.6-5.0 l/min) were compared regarding blood lactate responses, glycogen usage, and endurance during submaximal exercise. Seven subjects reached their blood lactate threshold (LT) during exercise of a relatively low intensity (group L) (i.e., 65.8 +/- 1.7% VO2 max), whereas exercise of a relatively high intensity was required to elicit LT in the other seven men (group H) (i.e., 81.5 +/- 1.8% VO2 max; P less than 0.001). Time to fatigue during exercise at 88% of VO2 max was more than twofold longer in group H compared with group L (60.8 +/- 3.1 vs. 29.1 +/- 5.0 min; P less than 0.001). Over 92% of the variance in performance was related to the % VO2 max at LT and muscle capillary density. The vastus lateralis muscle of group L was stressed more than that of group H during submaximal cycling (i.e., 79% VO2 max), as reflected by more than a twofold greater (P less than 0.001) rate of glycogen utilization and blood lactate concentration. The quality of the vastus lateralis in groups H and L was similar regarding mitochondrial enzyme activity, whereas group H possessed a greater percentage of type I muscle fibers (66.7 +/- 5.2 vs. 46.9 +/- 3.8; P less than 0.01). The differing metabolic responses to submaximal exercise observed between the two groups appeared to be specific to the leg extension phase of cycling, since the blood lactate responses of the two groups were comparable during uphill running. These data indicate that endurance can vary greatly among individuals with an equal VO2 max.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed1987

Endurance training effects on striatal D2 dopamine receptor binding and striatal dopamine metabolites in presenescent older rats.

Endurance training is associated with higher binding of 3H-spiperone to striatal D2 dopamine receptors of rats sacrificed 48 h following the last exercise bout (Gilliam et al. 1984). In the present study we investigated the effects of endurance training in presenescent older rats on the relationship between steady-state levels of DA and its metabolites in striatum versus the affinity and density of striatal D2 DA receptors. Citrate synthase activity of the gastrocnemius-plantaris muscle was 29.06 +/- 2.27 mumole/g wet wt in 21-month-old trained rats versus 22.88 +/- 1.13 mumole/g wet wt in 21-month-old untrained animals. DOPAC levels and DOPAC/DA ratios were greater in the old controls. Endurance training was associated with lower DOPAC levels in the 21-month-old animals. Thus, endurance training may postpone selectively changes in DA metabolism over a portion of the lifespan. As expected, the number of D2 DA binding sites was reduced with age (6 months Bmax:429 +/- 21 fmoles/mg protein; 21 months:355 +/- 20) with no change in affinity. The Bmax of old runners was significantly higher (457 +/- 38 fmoles/mg protein) than that of old controls. Thus, endurance training appears to exert a protective effect on D2 dopamine receptors during the lifespan. Taken together, the present results suggest that there may be a possible reciprocal relationship between changes in DA metabolites and DA binding as a function of exercise in presenescent older rats, and that endurance training may decelerate the effects of age both on nigrostriatal dopamine neurons and on striatal D2 dopamine receptors during a portion of the lifespan.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1985

Substrate usage during prolonged exercise following a preexercise meal.

The effect of a high-carbohydrate meal 4 h before 105 min of exercise at 70% of maximal O2 uptake was determined in seven endurance-trained cyclists and compared with exercise following a 16-h fast. The preexercise meal produced a transient elevation of plasma insulin and blood glucose, which returned to fasting basal levels prior to the initiation of exercise. The meal also resulted in a 42% elevation (P less than 0.05) of glycogen within the vastus lateralis at the beginning of exercise. The 1st h of exercise when subjects were fed was characterized by a 13-25% decline (P less than 0.05) in blood glucose concentration, a suppression of the normal increase in plasma free fatty acids and blood glycerol, and a 45% (P less than 0.05) greater rate of carbohydrate oxidation compared with exercise when subjects were fasted. After 105 min of exercise, there were no significant differences when subjects were fed or fasted regarding blood glucose levels, rate of carbohydrate oxidation, or muscle glycogen concentration. The greater muscle glycogen utilization (97 +/- 18 vs. 64 +/- 8 mmol glucosyl units X kg-1; P less than 0.05) and carbohydrate oxidation when subjects were fed appeared to be derived from the glycogen synthesized following the meal. These results indicate that preexercise feedings alter substrate availability despite a return of plasma insulin to fasting levels prior to exercise and that these effects persist until the 2nd h of exercise.

Bicycling↗

PubMed1984

The effects of exercise training on [3H]-spiperone binding in rat striatum.

Thirty male Sprague-Dawley rats 100 days of age were divided into three groups: interval trained, endurance trained, and pair-weighted controls. Both trained groups ran up to one hour per day, 6 days per week for 12 weeks. The interval trained group ran up to 20 repeat intervals at 54 meters per minute for 30 seconds, while the endurance trained group ran at 27 meters per minute for 60 minutes. The animals were sacrificed, and the effects of aerobic training were documented by measuring cytochrome oxidase activity in the mixed quadriceps muscles. The cytochrome oxidase activity of the interval and endurance trained groups increased 49%, and 31% respectively, above the control group. [3H]-spiperone was used to label dopamine receptors in the striatum. The endurance group was not significantly different from the interval group in [3H]-spiperone receptor binding, so the two exercise groups were combined to form one group of runners. The runners had significantly higher [3H]-spiperone receptor binding than the controls, F(1,26) = 4.87, p less than 0.05. The mean and standard error for receptor binding was 89 +/- 13 fmoles/mg protein for the runners and 60 +/- 5 fmoles/mg protein for the controls.

Animals↗

PubMedDate not supplied

Uncoupling of changes in skeletal muscle beta-adrenergic receptor density and aerobic capacity during the aging process.

The results of the present study indicate that the density of the beta-adrenergic receptors in the skeletal muscle does not decline with age, despite declines in oxidative capacity both in the skeletal muscle and whole body oxygen consumption. When young rats and old rats of equal body weight trained daily at the same duration and speed for 6 months on the treadmill, skeletal muscle of young and old rats reached the same aerobic capacity. The young demonstrated a significant rise in Bmax of the beta receptors, while the old rats did not change their density of receptors. When both young and old rats had the contractile activity of their skeletal muscle raised to the same level through chronic tonic electrical stimulation, the aerobic-capacity and beta receptor density rose to the same levels in the skeletal muscle. Thus, the contraction-dependent pathway in the senescent muscle appears to function normally given a maximal chronic stimulus via electrical stimulation. These data indicate that the relationship between oxidative capacity, beta-adrenergic receptor properties, exercise training, and aging does not appear to be readily explicable by a single unifying mechanism, but probably resides in the interaction of age with a differential responsiveness of the beta-adrenergic and/or contraction dependent pathway for stimulation of aerobic capacity in the aging skeletal muscle.

Aging↗