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Biomedical subjects

W S Barnes

Publications and source records attributed to W S Barnes.

At least 37 records · Page 2Linked to original sources
PubMed1988

Mechanisms of differential strain sensitivity in gastric carcinogenesis.

The genetically-controlled, distinct sensitivity of different rat strains to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced cancer of the glandular stomach and duodenum was investigated. MNNG is activated through thiols, and the thiol content of the glandular stomach, duodenum, and liver of the BN rat tended to be slightly, but not significantly higher than that of the Wistar, Sprague-Dawley, Lewis, and Buffalo rats. The levels of the DNA repair system, O6-alkylguanine transferase (AGT), in sensitive Wistar strain rats had values similar to those in resistant Buffalo strain rats. Administration of 80 mg/liter of MNNG in the drinking water for six weeks up to the time of tissue collection yielded the same AGT levels. Of all the parameters examined to account for genetically-mediated sensitivity to gastrointestinal cancer induction, namely, N-denitrosation, thiol activation, AGT-related DNA repair, and cell duplication rates, the latter yielded the best association, although these factors acting together may be involved.

Animals↗
PubMed1988

Caffeine, maximal power output and fatigue.

The purpose of this investigation was to determine the effects of caffeine ingestion on maximal power output and fatigue during short term, high intensity exercise. Nine adult males performed 15 s maximal exercise bouts 60 min after ingestion of caffeine (7 mg.kg-1) or placebo. Exercise bouts were carried out on a modified cycle ergometer which allowed power output to be computed for each one-half pedal stroke via microcomputer. Peak power output under caffeine conditions was not significantly different from that obtained following placebo ingestion. Similarly, time to peak power, total work, power fatigue index and power fatigue rate did not differ significantly between caffeine and placebo conditions. These results suggest that caffeine ingestion does not increase one's maximal ability to generate power. Further, caffeine does not alter the rate or magnitude of fatigue during high intensity, dynamic exercise.

Adult↗
PubMed1988

Depressing effects of calcium antagonists on oxygen consumption in isolated skeletal muscle during potassium depolarization.

The effects of two Ca2+-antagonizing drugs, dantrolene sodium (DAN) and TMB-8, on subcontracture, K+-induced increased oxygen consumption were studied in isolated frog sartorius muscles. Incubation in Ringer's solution +18 mM KCl caused a marked increase in averaged resting oxygen uptake (52.8 +/- 4.1 to 278.2 +/- 20.0 mm3.g-1.h-1). Incubation in Ringer's +18 mM KCl containing either 0.116 mM TMB-8 or 0.035 mM DAN resulted in a significant reduction in the averaged metabolic response (264.4 +/- 30.8 (control) vs. 142.3 +/- 19.0 (TMB-8) vs. 72.2 +/- 3.4 (DAN]. The results suggest that the enhanced metabolic rate observed upon elevating extracellular [K+] to just below contracture levels is due to increased intracellular Ca2+ release.

Animals↗
PubMed1988

A constant-load ergometer for measuring peak power output and fatigue.

A constant-load cycle ergometer was constructed that allows maximal power output to be measured for each one-half pedal revolution during brief, high-intensity exercise. To determine frictional force, an electronic load cell was attached to the resistance strap and the ergometer frame. Dead weights were attached to the strap's free end. Flywheel velocity was recorded by means of a magnetic switch and two magnets placed on the pedal sprocket. Pedaling resulted in magnetically activated switch closures, which produced two electronic pulses per pedal revolution. Pulses and load cell output were recorded (512 Hz), digitized, and stored on disk via microcomputer. Power output was later computed for each pair of adjacent pulses, representing average power per one-half pedal revolution. Power curves generated for each subject were analyzed for peak power output (the highest one-half pedal revolution average), time to peak power, power fatigue rate and index, average power, and total work. Thirty-eight males performed two 15-s tests separated by 15 min (n = 16) or 48 h (n = 22). Peak power output ranged from 846.0 to 1,289.1 W. Intraclass correlation analysis revealed high test-retest reliability for all parameters recorded on the same or different days (R = 0.91-0.97). No significant differences (P greater than 0.05) were noted between parameter means of the first and second tests. These results indicate that the ergometer described provides a means for conveniently and reliably assessing short-term power output and fatigue.

Ergonomics↗
PubMed1987

Respiration and lactate production in isolated frog skeletal muscle: effects of passive stretch.

The effects of varying degrees of passive stretch on in vitro oxygen consumption and intracellular lactate efflux have been investigated in paired recti abdomini muscles from small male frogs. Oxygen consumption [mm3 (STP)/mg (dry wt)/hr] was found to be linearly related to load (r = 0.98), increasing from 1.57 +/- 0.11 (SE) at 2 g to 2.30 +/- 0.18 at 10 g, 2.89 +/- 0.16 at 20 g and 3.26 +/- 0.21 at 30 g. Lactate released into the medium [microM/g (dry wt)/hr] was inversely related to load (r = -0.52), increasing initially from 36.84 +/- 3.28 (SE) at 2 g to 108.55 +/- 12.9 at 10 g, then abruptly decreasing with additional loading (18.10 +/- 2.60 at 20 g and 11.71 +/- 2.80 at 30 g). Results suggest that as stretch-related oxidative energy metabolism increases, there is a lessening dependence on anaerobic energy-yielding processes.

Animals↗
PubMed1987

Effects of ischemia on myo-electrical signal characteristics during rest and recovery from static work.

Twenty male college students served as subjects for a study which investigated how artificially-induced ischemia, with and without muscular fatigue, affects the: 1) input/output (IEMG/Force) relationship, and 2) power density spectrum of EMG signals during submaximal static contractions. In the first experiment, subjects maintained constant-force (60% MVC) static handgrip contractions for 55 sec. Following exercise, EMG mean power frequency (MPF) was significantly (P less than 0.05) reduced and EMG amplitude (rmsEMG) was significantly (P less than 0.05) increased. With circulation intact during 5 min recovery, MPF and rmsEMG values returned to pre-exercise levels. With ischemic recovery, MPF remained significantly (P less than 0.05) lower than pre-exercise values, while rmsEMG returned to approximately normal levels. In the second experiment, subjects performed either 3 sec ramp (90 N/sec) or constant-force (40% MVC) contractions immediately before, during the final 3 sec of, and 1, 3, 5 and 10 min after a 10 min tourniquet application. No statistically significant differences (P greater than 0.05) in the IEMG/Force slope coefficients, IEMG/Force ratios or MPF were observed for subjects performing either static ramp or constant-force contractions following temporary ischemia. Results suggest that reduced blood flow may contribute to fatigue-induced EMG changes. However, in the absence of motor activity, ischemia is an insufficient stimulus to cause either increased amplitude or frequency shift of the EMG signal during static contractions.

Action Potentials↗
PubMed1987

Influence of caffeine on force and EMG in rested and fatigued muscle.

At present, it is unclear how caffeine induced alterations in neuromuscular function might affect force production and EMG signal characteristics during isometric exercise. These data suggest that acute caffeine ingestion (7 mg/kg) has no significant effect on force production during a maximal isometric hand grip contraction or endurance during a sustained submaximal contraction. Further, maximal motor unit activation, the relationship between submaximal motor unit activation and subsequent force production, and frequency content of the EMG signal were not significantly altered following caffeine ingestion. These results indicate that although caffeine may be a potential ergogenic aid for some activities, its ingestion may not improve performance in activities requiring strength and/or short-term endurance.

Adult↗
PubMed1986

Fibrinolytic therapy in bacterial endocarditis: experimental studies in dogs.

An investigation was undertaken to assess the value of adding streptokinase therapy to standard penicillin treatment of artificially induced infective endocarditis due to Streptococcus sanguis. In pigs a low-grade infection could be induced which closely simulated streptococcal endocarditis in man, but for technical reasons this model proved unsatisfactory for further experimentation. In dogs the induction of S. sanguis endocarditis produced a more severe illness with a short natural history. Dogs were divided into two groups, one treated with penicillin alone, the other with penicillin and streptokinase. A five-day course, in which twice daily injections of an acylated streptokinase-plasminogen complex were given, caused a substantial reduction in the size of vegetations and possibly a higher proportion of cures and less damage to the valves. Infarction of the brain, almost certainly due to embolism, was significantly greater in the streptokinase treated group, but the same was not true of the kidneys. The possible value of such treatment for certain kinds of bacterial endocarditis in man, especially in the right side of the heart, is discussed.

Animals↗
PubMed1986

Genotoxicity, carcinogenicity, and mode of action of the fried food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ).

Because mutagens typified by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) observed in cooked foods are widely consumed, detailed studies of their biochemical and biological properties including carcinogenicity are most important. IQ induces unscheduled DNA synthesis in liver cells, which when taken together with its powerful mutagenicity in the Salmonella typhimurium test system, predicts carcinogenicity. In female Sprague-Dawley rats, IQ did exhibit potent carcinogenicity for the mammary gland, the ear duct, and to a lesser extent, pancreas and bladder. Data from Japanese laboratories indicate carcinogenicity also to the intestinal tract. Thus, one of the mutagens formed during cooking is a versatile carcinogen that because of extensive human intake requires urgent exploration for specific human cancer risk.

Animals↗
PubMed1986

Primary malignant cardiac tumors in children.

A child with a primary malignant cardiac tumor prompted a review of all 13 cases reported in Great Britain from 1962-1983. Only 4 definitely malignant tumors were identified, giving an incidence of between 1 in 38 and 1 in 90 x 10(6). All 4 patients died without evidence of metastases. Cardiac transplantation should be considered.

Chest Pain↗
PubMed1985

Glycogen utilization in isolated frog muscle: an effect of passive mechanical stretch.

The effect of passive mechanical stretch on glycogen utilization and total protein maintenance in paired sartorii muscles from small male frogs has been investigated, in vitro. Glycogen content of stretched muscles decreased 72.6% over a 24-hr incubation period, compared to a 23.1% decline in unstretched control muscles. Stretched muscles retained 54.7% of their total protein content over a 24-hr period, compared to 38.4% in the unstretched control muscles. Unstretched muscles demonstrated a significant (11.1%) increase in wet weight following 24 hr of incubation, presumably due to increased water retention. There were no significant changes in the wet wts of stretched muscles.

Animals↗
PubMed1985

Metabolic differentiation of red and white skeletal muscle in vivo and in monolayer culture.

Cytochrome oxidase, succinate oxidase and lactate dehydrogenase were compared in: (a) leg and breast muscle from 11-19-day-old chick embryos; and (b) 2, 6, 10 and 14-day-old primary cell cultures established from myoblasts of embryonic leg and breast muscle. Cytochrome oxidase, succinate oxidase and lactate dehydrogenase activities were higher (48.8, 65.4, 277.6%, respectively) in leg muscle after 19 days in ovo. Cytochrome and succinate oxidase activities were higher (111.3, 48.1%, respectively) in leg muscle cell cultures after 14 days in vitro. The data represent evidence for intrinsic developmental patterns for certain enzymes.

Animals↗
PubMed1985

Genotoxicity of the food mutagen 2-amino-3-methylimidazo-[4,5-f]quinoline (IQ) and analogs.

The food mutagen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) is an analogue of quinoline, a hepatocarcinogen. 2-Aminofluorene, benzidine and 3,2'-dimethyl-4-aminobiphenyl (DMAB) are potent inducers of unscheduled DNA repair in primary culture rat liver hepatocytes, as was IQ (151 grains/nucleus at 1 X 10(-6) M). Quinoline, on the other hand, is only weakly positive in this assay (15 grains/nucleus at 1 X 10(-3) M). IQ, quinoline and DMAB were applied topically to shaved skin of Sencar mice with promotion by 12-O-tetradecanoylphorbol 13-acetate (TPA) for 20 weeks, when 14 of 20 mice in the quinoline group had 25 tumors, but only one of 30 animals in the IQ group and five of 30 in the DMAB group were tumor-bearing. Analogs of IQ synthesized by substitution at the 2- or 3-position with amino or methyl groups were assayed with the Ames Salmonella typhimurium tester strains TA98 and TA100. Mutagenicity for TA98 is reduced in the absence of the 3-methyl group and is completely abolished with removal of the 2-amino moiety. None of these analogs are strong mutagens for TA100. Exocyclic N-oxidation is a likely obligatory step in the activation of IQ to a mutagen.

Animals↗