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Biomedical subjects

R B Armstrong

Publications and source records attributed to R B Armstrong.

At least 109 records · Page 6Linked to original sources
PubMed1983

Blood flows within and among rat muscles as a function of time during high speed treadmill exercise.

The purpose of these experiments was to use radiolabelled microspheres to measure blood flow distribution patterns within and among rat hind-limb skeletal muscles before, during, and after high speed treadmill running at 60 min-1 to fatigue. Exercise blood flows were measured at the 0.5, 1, 2 and 3 min time points. Pre-exercise blood flow was highest in physiological extensor muscles or muscle parts with large populations of slow-twitch muscle fibres, e.g. soleus (197 ml min-1 100 g-1). Blood flows were lowest to muscles or muscle parts with high proportions of fast-twitch glycolytic fibres, e.g. white gastrocnemius (15 ml min-1 100 g-1). The most rapid increases in blood flow at the beginning of exercise and the highest peak blood flows during exercise generally occurred in physiological extensor muscles with relatively high populations of fast-twitch oxidative fibres. For example, red gastrocnemius muscle blood flow increased by 271 ml min-1 100 g-1 during the first 30 s of exercise, and attained a peak flow of 395 ml min-1 100 g-1 by the third minute of exercise. On the other hand, the slowest elevations in blood flow at the start of exercise and the lowest peak flows were observed in muscles with high populations of fast-twitch glycolytic fibres. White gastrocnemius muscle, for example, increased its blood flow by 16 ml min-1 100 g-1 during the first 30 s of running, and had a peak flow of 76 ml min-1 100 g-1 by the end of 3 min exercise. These relationships between blood flows and fibre type populations were less consistent in physiological flexor muscle groups. Following exercise, blood flows in high-oxidative muscles returned to the pre-exercise levels within 30 s. However, in low-oxidative muscles, return of blood flows to the pre-exercise levels were slower. Thus, marked differences in the absolute magnitudes of blood flows and in the rates of change in blood flows were observed within and among the hind-limb muscles before, during and after exercise. These differences were related to the fibre type compositions of the muscles.

Animals↗
PubMed1983

Rat muscle blood flows as a function of time during prolonged slow treadmill exercise.

The purpose of these experiments was to follow blood flows (BF) within and among rat hindlimb skeletal muscles as a function of time during prolonged low-speed treadmill locomotion. Male Sprague-Dawley rats were chronically instrumented with two Silastic catheters, one in the ascending aorta via the right carotid artery for microsphere infusion and one in the left renal artery for arterial reference blood sample withdrawal. BFs were measured, using the radio-labeled microsphere technique, within and among 23 major skeletal muscles of rats before exercise and during treadmill locomotion at 15 m/min at 0.5, 1, 5, 15, 30, 54, and 71 min of exercise. During preexercise, BF was highest to deeply situated slow-twitch muscles (210 ml . min-1 . 100 g-1 in vastus intermedius) in the antigravity extensor muscle groups. During the 1st min of exercise each of the hindlimb muscles displayed one of four general BF patterns. 1) Many muscles had an "overshoot" in BF during the first 30 s of exercise; 2) some muscles attained steady-state exercise levels in the first 30 s of exercise; 3) others showed a decrease below preexercise levels; and 4) some muscles showed no change from preexercise. Most muscles showed a gradual increase in BF from 5 min through 54 min of exercise. The elevations in BF over preexercise were primarily directed to fast-twitch oxidative muscle fibers in the antigravity extensor muscles, and BFs to extensor muscle groups were generally higher than those to flexor muscle groups. The data demonstrate that BFs within and among rat muscles are heterogeneous, both before exercise and during prolonged low-intensity treadmill walking to fatigue. Mechanisms regulating the distribution of flow to the muscles remain to be elucidated.

Adipose Tissue↗
PubMed1983

Eccentric exercise-induced injury to rat skeletal muscle.

These experiments were designed to study skeletal muscle pathology resulting from eccentric-biased exercise in rats. The effects on the muscles of running on a treadmill on a 0 degrees incline (similar amounts of concentric and eccentric contractions), down a 16 degrees incline (primarily eccentric contractions), and up a 16 degrees incline (primarily concentric contractions) at 16 m . min-1 for 90 min were assessed by following postexercise changes in 1) plasma creatine kinase and lactate dehydrogenase activities, 2) glucose-6-phosphate dehydrogenase (G-6-PDase) activity (bio- and histochemically) in the physiological extensor muscles, and 3) histological appearance of the muscles. The data indicate the following. 1) Whereas all exercise protocols resulted in elevations of plasma enzymes immediately after running, only eccentric exercise caused late phase elevations 1.5-2 days postexercise. 2) Significant increases in muscle G-6-PDase activity, which were always associated with accumulations of mononuclear cells, always occurred within some muscles of each extensor group 1-3 days following downhill and uphill running and did not occur following level running; the increases in activity were usually of lower magnitude in the muscles of uphill runners than in those of downhill runners; the deeply located, predominantly slow-twitch muscles were most affected by both down- and uphill running. 3) Muscle histology demonstrated localized disruption of normal banding patterns of some fibers immediately after exercise and accumulations of macrophages in the interstitium and in some (less than 5%) muscle fibers by 24 h postexercise in the deep slow muscles of the antigravity groups. Although the data generally indicated that eccentric exercise causes greater injury to the muscles, questions remain.

Animals↗
PubMed1983

Metabolism of rats running up and down an incline.

The purpose of these experiments was to determine oxygen consumption (VO2) in rats as a function of treadmill speed (10, 20, 30, 40, and 50 m . min-1) as they ran on the level and up and down a 16 degree (17.8%) incline. The slopes of the regression lines relating VO2 (ml O2 . kg-1 . min-1) to running speed (m . min-1) were linear for all three inclines. The regression slope for uphill runners (y = 1.25x + 47.7) was greater than the regression slopes for level (y = 0.88x + 41.2) (P less than 0.025) or downhill (y = 0.68x + 39.7) (P less than 0.005) runners, and the regression slope for level runners was greater than that for downhill runners (P less than 0.10). All VO2 measurements were submaximal. In conclusion, incline has a significant effect on the metabolism of rats running on a motor-driven treadmill.

Animals↗
PubMed1983

Effect of training on skeletal muscle injury from downhill running in rats.

Experiments were conducted to test the hypothesis that injury to skeletal muscle in rats resulting from prolonged downhill running is prevented to a greater extent by prior downhill training than by either uphill or level training. Changes in plasma creatine phosphokinase (CPK) activity and glucose-6-phosphate dehydrogenase (G-6-PDase) activity in the soleus (S), vastus intermedius (VI), and medial head of triceps brachii (TM) muscles were evaluated as markers of muscle injury 48 h after 90 min of intermittent downhill running (16 m . min -1). Prior to this acute downhill run, groups of rats were trained by either downhill (-16 degrees), level (0 degrees), or uphill (+16 degrees) running (16 m . min -1) for 30 min/day. Training duration was either 5 days or 1 day. A training effect (i.e., reduced muscle injury) was indicated if muscle G-6-PDase or plasma CPK activity in a trained group following the 90-min downhill run was not different from that of nonexercised control animals and/or if it was lower than that of nontrained runners. A significant training effect was achieved in all three muscles with 5 days of either downhill or level training, but only in S after 5 days of uphill training. Elevation of plasma CPK activity was prevented by 5 days of training on all three inclines.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Influence of circadian rhythms on rat muscle glycogen metabolism during and after exercise.

Marked circadian fluctuations in skeletal muscle glycogen concentrations have previously been reported. The purpose of the present study was to estimate the influence of these rhythms on muscle glycogen metabolism during and after high-intensity treadmill exercise. Male Sprague-Dawley rats ran five 1-min sprints at 75 m min-1 interspersed by 1-3 min rest intervals either at 08.00 h (morning) or at 20.00 h (night). All muscles sampled lost significant amounts of glycogen during exercise at both time periods. There were no differences in rates of loss between morning and night, even though glycogen levels in several muscles (high-oxidative muscles) were significantly higher before exercise in the morning. Following exercise, glycogen restoration in muscle samples primarily composed of fast-twitch fibres was more rapid in the morning than at night. There was no difference in glycogen restoration rates between the two time periods in the muscle primarily composed of slow-twitch fibres. Although liver glycogen was lower after exercise at night than in the morning, there were no differences in post-exercise blood glucose levels between the two time periods. In conclusion, circadian rhythms do not appear to influence rates of glycogen loss during high-speed running. However, since glycogen loss is the same at all times of day, one would predict that circadian changes in pre-exercise muscle glycogen concentrations would affect muscular endurance. Muscle glycogen restoration after exercise does appear to be affected by circadian rhythms, although interpretation of these data is complicated by possible changes in patterns of muscle fibre contraction at different times of the day. These circadian influences should be considered in the design of exercise studies using laboratory rodents.

Animals↗
PubMed1983

Hormonal influence on diurnal glycogen rhythms in rat skeletal muscles.

1. Normal, diabetic, and sympathectomized rats were killed at intervals during a 12 h light (6 a.m. to 6 p.m.)/12 h dark cycle to determine (1) the patterns of diurnal glycogen rhythms in skeletal muscle fibre types, and (2) if the absence of insulin or the catecholamines epinephrine and norepinephrine abolished these rhythms. 2. Normal rat muscles lost and restored 40-60% of their glycogen stores during one 24-h cycle. Glycogen losses were linear between 6.30 a.m. (acrophase time for all muscles) and 8.30 a.m. and between 8.30 a.m. and nadir points (4.30 p.m. to 8.30 p.m.), but the rates of loss were non-uniform between these time frames and among fibre types. All muscles had similar linear restoration rates. 3. Glycogen stores in most muscles from diabetic and sympathectomized rats exhibited changes similar to those seen in normal animals. 4. Skeletal muscle fibre types have notable and non-uniform diurnal glycogen rhythms that should be considered in the design of metabolic and exercise experiments. These rhythms do not appear to be regulated, either differentially or in toto, either by insulin or by the catecholamines epinephrine and norepinephrine.

Adrenal Glands↗
PubMed1983

Delayed-onset muscular soreness and plasma CPK and LDH activities after downhill running.

We tested the hypothesis that running down an incline, during which muscles primarily perform eccentric contractions, causes greater delayed-onset muscle soreness and greater increases in plasma enzyme activities than does running on the level, during which muscles perform similar amounts of concentric and eccentric contractions. Subjective sensations of muscular soreness and plasma activities of CPK and LDH were assessed in seven subjects at 0, 24, 48, and 72 h after 45 min of running (one time on the level and a second time down a 10% incline). Following downhill running (57% of VO2max), significant delayed-onset soreness was experienced in gluteal, quadricep, anterior leg, and posterior leg muscles, and plasma CPK (but not LDH) activity was significantly increased (351% at 24 h). In contrast, following level running (78% of VO2max), no statistically significant soreness occurred in any muscle group, and plasma CPK and LDH activities were not elevated. Thus, our results generally support the hypothesis. Secondarily, we investigated whether delayed-onset soreness with downhill running is accompanied by increases in peripheral white blood cell counts suggestive of inflammation. No such association was observed. We suggest that both delayed-onset muscular soreness and plasma enzyme activities are affected by structural changes in muscle tissue resulting from eccentric contractions.

Adult↗
PubMed1982

Solar urticaria. Clinical features and wavelength dependence.

Solar urticaria, an uncommon photosensitivity disorder, may be disabling for affected patients, especially those who react after short exposures to artificial or natural light. The spectrodermograph, a newly developed instrument, permits rapid, accurate determination of the action spectrum of solar urticaria. It consists of a xenon arc lamp with an emission dispersed into used to establish the wavelengths responsible for solar urticaria in 12 patients during the past four years. Knowledge of the wavelengths responsible for producing the urticarial reaction has implications for selecting appropriate therapy. The clinical course of these patients is also reviewed.

Adolescent↗
PubMed1982

Distribution of fiber types in locomotory muscles of dogs.

The distribution of Type I and Type II fibers, as determined from histochemical estimation of myofibrillar ATPase activity, was studied within and among the locomotory muscles of the forelimb, trunk, and hindlimb of three mongrel dogs. All Type II fibers had high oxidative capacities as estimated from the histochemical assay for reduced nicotinamide adenine dinucleotide tetrazolium reductase, so they were not further divided into subpopulations. Furthermore, Type I and Type II fibers had similar oxidative potentials as indicated by both histochemistry and biochemistry. Type I fiber populations ranged between 14% and 100% in the muscles sampled. The highest percentages of Type I fibers were found in deep muscles of physiological extensor groups in the arm and thigh that serve to resist gravity (antigravity muscles) when the dog is in the quadrupedal standing position. More superficial muscles in these same groups had fewer Type I fibers. The patterns of Type I fiber distribution among muscles in the antigravity groups of the forearm and leg were the opposite of those in the arm and thigh, with the more superficial muscles of the distal limb segments having more Type I fibers than the deeper muscles. In all limb segments, muscle groups that do not serve to resist gravity did not show as much intermuscular variation. Type I fiber populations in these muscles did not exceed 50%. A stratification of fiber types also existed within muscles, both in extensor and flexor groups, with the deeper portions of the muscles having more Type I fibers than the more superficial portions.

Adenosine Triphosphatases↗
PubMed1982

Muscular blood flow distribution patterns as a function of running speed in rats.

Muscle blood flow (BF) was measured using the radiolabeled microsphere technique within and among nine major muscles of rats before exercise and during treadmill walking or running at speeds of 15, 30, 45, 60, and 75 m/min. Measurements were made during exercise after 1 min of steady walking or running. Male Sprague-Dawley rats were chronically instrumented with 2 Silastic catheters, one in the ascending aorta via the right carotid artery for microsphere infusion and one in the left renal artery for arterial reference blood sample withdrawal. The preexercise results demonstrated that 1) BF to deep slow-twitch muscles was three to four times that to peripheral fast muscles (e.g., soleus and gastrocnemius BFs were 138 and 33 ml . min-1 . 100 g-1, respectively); 2) BFs to red portions within mixed muscles were three to four times those to white portions (e.g, red and white gastrocnemius BFs were 54 and 18 ml . min-1 . 100 g-1, respectively; and 3) there was a direct relationship (P less than 0.05) between BFs to muscles and their slow-twitch oxidative fiber populations. The results obtained during exercise demonstrated that 1) at the slowest speed studied (15 m/min) BFs to the red portions of muscles increased, whereas BFs to the white portions of the same muscles decreased; 2) BFs to all muscles (except soleus) were increased during running at 75 m/min when there was a range of flows of 30 ml . 100 g-1 . min-1 (white gastrocnemius) to 321 (vastus intermedius), 3) at all running speeds the increases in BF to muscles were directly related to the fast-twitch, high-oxidative fiber populations of the muscles; and 4) BFs to visceral tissues and fat were decreased during exercise.

Animals↗
PubMed1982

A method for using microspheres to measure muscle blood flow in exercising rats.

A catheter-implantation procedure allowing use of the radiolabeled microsphere (MS) technique for measuring skeletal muscle blood flow (BF) in rats during high-speed treadmill running was desired. Attempts to use existing procedures were unsuccessful. We found that Silastic catheters (0.02 in. ID X 0.037 in. OD) placed in the ascending aorta (for MS infusions) and the renal artery (for reference sample withdrawal) minimized these exercise performance problems. It was then necessary to establish that aortic MS infusions result in good MS-blood mixing. We tested the method with the following: 1) the radioactivities found in reference withdrawal samples taken from two locations in the aorta were compared after left ventricular (LV) infusion and after aortic infusion; 2) BFs to bilaterally paired tissues were compared in anesthetized and conscious rats with LV and aortic infusions; 3) the distribution of MSs in the muscles was studied histologically; and 4) BFs in bilaterally paired tissues were compared in rats with aortic MS infusions during treadmill running. The results indicate that 1) the percent difference between the radioactivities found in the proximal and distal reference withdraw samples was the same for LV and aortic MS infusions; 2) BF to bilaterally paired tissue samples was the same with both LV or aortic MS infusions; 3) the MSs were distributed uniformly within muscles, and MS aggregation was not a significant problem; and 4) BFs to bilaterally paired tissue samples were the same in exercising rats. We conclude that this technique can be used to measure muscle BF in rats running on a treadmill.

Animals↗
PubMed1982

Relationship between muscle force and muscle area showing glycogen loss during locomotion.

This experiment was designed to study the relationship between the cross-sectional area of rat skeletal muscle showing glycogen loss and the muscle forces exerted during exercise. Muscular force exerted by the extensors of the elbows and ankle was increased by 24% by loading rats with 24% of their body mass while running them on a treadmill at 30 m.min-1. VO2 increased by 24% and stride frequency was unchanged when the rats ran with loads. Cross-sectional areas of the elbow and ankle extensor muscles showing glycogen loss were compared from rats running with and without the load. We found a nearly direct proportionality between the changes in force and the changes in muscle area showing glycogen loss, i.e. when the force of the extensors was increased by 24%, the cross-sectional area of the elbow extensors showing glycogen loss increased by 28%, and that of the ankle extensor group increased by 24%. The more peripheral muscles in each group accounted for a greater proportion of the increase in cross-sectional area of the group showing glycogen loss (i.e. lateral and long heads of triceps brachii muscle accounted for 91% of the increase in the elbow extensor group, and gastrocnemius muscle accounted for 84% of the increase in the ankle extensor group). Most of the increases in muscle area showing glycogen loss occurred in fast-twitch-glycolytic fibres (84% in the elbow and 88% in the ankle). The data suggest that increasing muscle force requirements by 24% by loading resulted in proportional increases in cross-sectional area of muscles recruited to produce the force, i.e. that spatial recruitment primarily accounted for the elevation in force. The relatively greater increases in cross-sectional area showing glycogen loss of peripheral muscles within a group indicate the importance of studying whole groups of muscles when considering muscular recruitment patterns during exercise.

Animals↗
PubMed1982

Current status of predictive animal models for drug photoallergy and their correlation with drug photoallergy in humans.

The number of adverse responses considered to be drug photosensitivity reactions account for only an exceedingly small percentage of the total undesirable effects from environmental chemicals. However, the rising incidence of and severe disability resulting from drug photosensitivity, especially when the photosensitivity is of the persistent light reactor type, indicate that increased photobiologic research and development efforts are required. Predictive tests are an obvious approach to minimize or eliminate those chemicals showing a risk-benefit ratio that is undesirable to society in general or to an unknowing individual in particular. Animal models with predictive value for determining the risk of photoallergic contact dermatitis in humans have undergone considerable modification during the past decade. This study reports an improved experimental guinea pig model for inducing photoallergic contact dermatitis to musk ambrette. In contrast to previously described models that used Freund's adjuvant, this model does not require nuchal stripping with cellophane tape. Control studies for primary irritancy, phototoxicity, allergic contact dermatitis, and "angry back" syndrome were included in the experimental design. Only photoallergic contact dermatitis was observed. Although the technique used to demonstrate this phenomenon is conducive to standardization, additional studies are required to ascertain whether or not other chemicals known to be photoallergic in humans can also be demonstrated with this animal model.

Animals↗
PubMed1982

Methotrexate and ultraviolet radiation.

Reactivation of a sunburn has been reported after the administration of methotrexate for cancer chemotherapy. A similar reaction is described in a patient with psoriasis who was receiving both coal tar with ultraviolet radiation for cutaneous lesions and methotrexate for arthritis. Knowledge of this poorly understood side effect of methotrexate is particularly important for physicians administering phototherapy and, perhaps, photochemotherapy.

Adult↗