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Biomedical subjects

D W Barnett

Publications and source records attributed to D W Barnett.

24 records · Page 2Linked to original sources
PubMed1991

Effects of cocaine on plasma catecholamine and muscle glycogen concentrations during exercise in the rat.

This study was designed to test the hypothesis that cocaine (C) alters the normal physiological responses to exercise. Male rats were injected with saline (S) or C (12.5 mg/kg) either intravenously (iv) or intraperitoneally (ip). After injection the animals were allowed to rest for 30 min or were run on the treadmill (26 m/min, 10% grade). At rest plasma epinephrine values were 245 +/- 24 pg/ml in the S group and 411 +/- 43 (ip) and 612 +/- 41 (iv) pg/ml in the C groups (P less than 0.05 between S and C). During exercise plasma epinephrine levels were 615 +/- 32 pg/ml in S and 1,316 +/- 58 (ip) and 1,208 +/- 37 (iv) pg/ml in the C groups (P less than 0.05 between S and C). Similar results were obtained for norepinephrine. Glycogen content in the white vastus lateralis muscle was reduced to 31 +/- 2 mumol/g in S after exercise, but after C and exercise the values were 12 +/- 4 (ip) and 16 +/- 3 (iv) mumol/g (P less than 0.05 between S and C). There was no effect of the drug on this parameter at rest. Blood lactate rose to 4.8 +/- 1.0 (ip) and 5.8 +/- 1.3 (iv) mM in the C groups but to only 3.0 +/- 0.2 in the S group after exercise (P less than 0.05 between S and C). These results show that C and exercise combined exert a more dramatic effect on plasma catecholamine, muscle glycogen, and blood lactate concentrations than do C and exercise alone. They provide further insight into explaining the adverse effects of C on exercise endurance observed previously (Bracken et al., J. Appl. Physiol. 66: 377-383, 1989).

Animals↗
PubMed1990

Glycogen repletion and exercise endurance in rats adapted to a high fat diet.

It is well accepted that exercise endurance is directly related to the amount of carbohydrate stored in muscle and that a low carbohydrate diet reduces glycogen storage and exercise performance. However, more recent evidence has shown that when the organism adapts to a high fat diet endurance is not hindered. The present study was designed to test that claim and to further determine if animals adapted to a high fat diet could recover from exhausting exercise and exercise again in spite of carbohydrate deprivation. Fat-adapted (3 to 4 weeks, 78% fat, 1% carbohydrates) rats (FAT) ran (28 m/min, 10% grade) as long as carbohydrate-fed (69% carbohydrates) animals (CHO) (115 v 109 minutes, respectively) in spite of lower pre-exercise glycogen levels in red vastus muscle (36 v 54 mumols/g) and liver (164 v 313 mumols/g) in the FAT group. Following 72 hours of recovery on the FAT diet, glycogen in muscle had replenished to 42 mumols/g (v 52 for CHO) and liver glycogen to 238 mumols/g (v 335 for CHO). The animals were run to exhaustion a second time and run times were again similar (122 v 132 minutes FAT v CHO). When diets were switched after run 1, FAT-adapted animals, which received carbohydrates for 72 hours, restored muscle and liver glycogen (48 and 343 mumols/g, respectively) and then ran longer (144 minutes) than CHO-adapted animals (104 minutes) that ate fat for 72 hours and that had reduced glycogen repletion. We conclude that, in contrast to the classic CHO loading studies in humans that involved acute (72 hours) fat feedings and subsequently reduced endurance, rats adapted to a high fat diet do not have a decrease in endurance capacity even after recovery from previous exhausting work bouts. Part of this adaptation may involve the increased storage and utilization of intramuscular triglycerides (TG) as observed in the present experiment.

Adaptation, Physiological↗
PubMed1989

Cocaine does not alter cardiac glycogen content at rest or during exercise.

Cocaine is a potent sympathomimetic drug, and has been implicated as a causative factor in cardiac seizures. However, little is known about the effect of the drug on myocardial substrate utilization. In the present study, rats were injected intravenously with saline solution or one of three doses of cocaine-HCl (1.25, 5.0, 10.0 mg/kg) and subsequently rested or exercised (22 m/min at 15% grade) for 20 minutes. Hearts were removed and frozen within 30 seconds after the injection of anesthetic and within 10 seconds after opening the thoracic cavity. The mean values for resting glycogen content ranged from 24.9 to 27.0 mumol/g, and for glucose-6-phosphate, from 0.27 to 0.30 mumol/g across groups. These values were unaffected by cocaine or exercise. We conclude, based on the conditions of this study, that cocaine has no direct or indirect effect on glycogen storage of the myocardium at rest or during exercise.

Animals↗
PubMed1984

The effects of a commercial dietary supplement on human performance.

Twenty male runners were recruited to test whether a commercial ergogenic supplement was of any physiological benefit to endurance performance. Either a placebo or the supplement (a vitamin, mineral, amino acid, and unsaturated fatty acid complex) was administered to the subjects in a dose of three capsules daily over a 4-wk period in a double-blind design. A 60-min submaximal treadmill run (65 to 70% VO2 max) and a max VO2 test were completed by each subject before and after supplementation. The results demonstrated that even though exercise caused a significant decrease in muscle glycogen (36 to 48%) and blood glucose (24 to 34%) levels and an increase in blood free fatty acid (350%) and lactate concentration (200 to 230%), these changes were similar for both placebo and supplement groups. Similarly, the supplement had no effect on maximum oxygen consumption. We conclude that the supplement had no beneficial effect on performance as indicated by its inability to alter significantly any of the metabolic or physiological parameters, and that supplements of this nature are of no physiological value to the athlete who consumes a normal nutritionally balanced diet.

Adolescent↗
PubMed1977

Validating a measure of children's others-concept through population and behavior variables.

Data are presented to support the Paired Hands Test (PHT) as a valid measure of the others-concept in children. This construct is defined as a person's general expectancies or perceptions about other people along a positive-negative continuum. Behavioral data are reported which replicate findings from earlier, smaller studies that children who have relatively high others-concepts are likely to interact more positively in small, unsupervised groups than children having relatively low others-concepts. Population data are also given, based upon 1,235 PHT test scores broken down by such variables as sex and socioeconomic status. Additionally, content validity inherent in the nature of the test is discussed. The conclusion drawn is that the data can be best explained by employing the others-concept as a theoretical construct measured by the PHT.

Journal Article↗