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PubMed2001

Physiological characteristics of nationally competitive female road cyclists and demands of competition.

There are few published data describing female cyclists and the studies available are difficult to interpret because of the classification of athletes. In this review, cyclists are referred to as either internationally competitive (International Cycling Union world rankings provided when available) or nationally competitive. Based on the limited data available it appears that the age, height, body mass (BM) and body composition of women cyclists who have been selected to the US and Australian National Road Cycling Teams from 1980 to 2000 are fairly similar. Female cyclists who have become internationally competitive are generally between 21 to 28 years of age, 162 to 174 cm, 55.4 to 58.8 kg and 38 to 51 mm (sum of 7 skinfolds) corresponding to 7 to 12% body fat. The lower BM and percentage body fat are traits unique to the most competitive women. Internationally competitive women cyclists also possess a slightly superior ability to produce a high absolute power output for a fixed time period and a noticeably greater ability to produce power output relative to BM. In Women's World Cup races, successful women (top 20 places) spend more time >7.5 W/kg (11 +/- 2 vs 7 +/- 2%, p < 0.01) and less time <0.75 W/kg (24 +/- 4 vs 29 +/- 3%, p = 0.05) compared with non-top 20 placed riders. Additionally, cyclists in the top 20 produced higher average power (3.6 +/- 0.4 vs 3.1 +/- 0.1 W/kg, p = 0.01). Unlike professional men's road cycling, the physiological characteristics of internationally competitive female road cyclists and the demands of women's cycling competition are poorly understood.

Adult↗
PubMed2003

Market competition: everybody is talking, but what do they say?. A sociological analysis of market competition in policy networks.

From providers and insurers to governments and consumers, it appears that everybody is talking about market competition in health care. However, what do they actually mean? Are they talking about the same things? These questions are relevant for health systems consisting of policy networks, such as in the Netherlands. In policy networks, different actors (besides the government) are engaged in policy-making. Based on their particular frame ('mode of interpretation'), actors proceed and, from this, give meaning to the concept of market competition. Since there are differences in frames (of reference) among the various actors, it is important to understand what market competition means from the perspective of each network participant. This study, with regard to the Dutch health care system, demonstrates 'market competition' as a broad concept, relating to 13 different frames. Only four frames (i.e. cost control, deregulation, competition and increased power) are shared by a maximum of two (out of a total of four) network participants. Clearly, there are differences in the meanings and underlying frames about market competition amongst the key players. The resulting implications and options for policy-making are discussed.

Consumer Organizations↗
PubMed2004

Risk allocation and competition in foraging groups: reversed effects of competition if group size varies under risk of predation.

Animals often feed more quickly when in larger groups. This group-size effect is often explained by safety advantages for groups but an alternative explanation is that animals feed faster in larger groups because of greater scramble competition for limited food. We show that predation risk enhances the group-size effect if groups vary in size. By contrast, competition leads to the group-size effect only when individuals feed in groups of constant size. When individuals feed in groups that vary in size, the best strategy for dealing with competition is to feed intensely when in smaller groups and feed little when in larger (more competitive) groups. In all situations, the effects of competition interact with the effects of predation risk in a simple multiplicative way. Our results suggest that scramble competition is not a general explanation for the group-size effect on vigilance in situations where group size changes relatively rapidly.

Animals↗
PubMed2001

The effects of competition and competitiveness on cardiovascular activity.

Cardiovascular activity was measured at resting baseline and in response to a car racing game, undertaken in competition or in cooperation with an experimenter, or individually. Competitiveness and win and goal orientations were assessed by questionnaire. Competition provoked increases in blood pressure and heart rate, and a significant shortening of the preejection period, an index of enhanced beta-adrenergic influences on the heart. The cooperation task was largely without effect, and although the solo task affected cardiovascular activity, it did so to a lesser extent and much less consistently than did the competition task. The three task conditions, then, were largely distinguishable by their capacity to activate beta-adrenergic processes. Participants high in competitiveness and desire to win showed higher blood pressure reactions and greater shortening of the preejection period to competition than those low in these characteristics.

Adult↗
PubMed2006

Within-host competition in genetically diverse malaria infections: parasite virulence and competitive success.

Humans and animals often become coinfected with pathogen strains that differ in virulence. The ensuing interaction between these strains can, in theory, be a major determinant of the direction of selection on virulence genes in pathogen populations. Many mathematical analyses of this assume that virulent pathogen lineages have a competitive advantage within coinfected hosts and thus predict that pathogens will evolve to become more virulent where genetically diverse infections are common. Although the implications of these studies are relevant to both fundamental biology and medical science, direct empirical tests for relationships between virulence and competitive ability are lacking. Here we use newly developed strain-specific real-time quantitative polymerase chain reaction protocols to determine the pairwise competitiveness of genetically divergent Plasmodium chabaudi clones that represent a wide range of innate virulences in their rodent host. We found that even against their background of widely varying genotypic and antigenic properties, virulent clones had a competitive advantage in the acute phase of mixed infections. The more virulent a clone was relative to its competitor, the less it suffered from competition. This result confirms our earlier work with parasite lines derived from a single clonal lineage by serial passage and supports the virulence-competitive ability assumption of many theoretical models. To the extent that our rodent model captures the essence of the natural history of malaria parasites, public health interventions which reduce the incidence of mixed malaria infections should have beneficial consequences by reducing the selection for high virulence.

Animals↗
PubMed1986

The origin and use of the terms competitive and non-competitive in interactions among chemical substances in biological systems.

The terms competition and competitive were in use for appropriate types of interaction in human and animal behaviour from the seventeenth century. In the nineteenth and early twentieth centuries they reached more technical uses in biology, especially in darwinian studies; and in chemistry in describing competing reactions, surface phenomena and the influence of substituent groupings in reactant molecules. Use of competitive and non-competitive to describe enzyme inhibitors had a specific beginning when J. B. S. Haldane (following premonitory work of others) applied the terms in 1927 and 1930 to types of inhibition already differentiated by Michaelis and co-workers. The theoretical background in kinetics and stereochemistry so acquired gave a firmness to the application of the terms in biochemistry. The first examples concerned glycosidases, especially beta-D-fructofuranosidase or invertase, and interactions of carbon monoxide and oxygen at iron-porphyrin systems. They were thus of interest in toxicology and in enzyme and carrier studies. The sphere of application of the biochemically-defined terms expanded greatly when, following investigation of sulphonamide action, it was realized that concepts of enzyme inhibition by structurally related compounds offered a route to understanding the action of existing medicaments and to the production of new ones. Ideas and terminology based on competitive and non-competitive enzyme inhibition and receptor occupancy have subsequently been applied in many ways. Examples include application to the analysis of feedback inhibition and other processes of metabolic control; to receptor relationships among neurotransmitters and medicaments; and to understanding interactions at sensory receptors.

Animals↗
PubMed1991

Genetic differences in the effects of competitive and non-competitive NMDA receptor antagonists on locomotor activity in mice.

The effects of non-competitive (MK-801, phencyclidine, and ketamine) and competitive (CGP 39551, CGS 19755, and NPC 12626) N-methyl-D-aspartate (NMDA) receptor antagonists on locomotor activity in inbred CBA and C57, and in outbred NMRI mice were examined. Administration of the non-competitive NMDA antagonists produced a dose-dependent increase in well-coordinated locomotor activity at lower doses, followed by a bizarre behavioral syndrome (head weaving, body rolling, rotations, ataxia) after higher doses. The pharmacological profile of the competitive antagonists CGP 39551, CGS 19755, and NPC 12626 was more complex. CGP 39551 dose-dependently inhibited locomotor activity, whereas CGS 19755 and NPC 12626 displayed a biphasic action, that is low doses inhibited locomotor activity, whereas higher doses produced mild behavioral stimulation. The behavioral effects of NMDA antagonists appear to be genetically determined, since CBA animals were most sensitive to both non-competitive and competitive antagonists, followed by NMRI and C57 animals. The differential effects of NMDA antagonists in various strains of mice suggest that the observed behavioral differences may be due to genetic differences in the NMDA/glutamate receptor channel complex.

Amino Acids↗
PubMed1989

A comparison of the anticonvulsant effects of competitive and non-competitive antagonists of the N-methyl-D-aspartate receptor.

The anticonvulsant activity of two competitive antagonists of the N-methyl-D-aspartate (NMDA) receptor, 2-amino-7-phosphonoheptanoic acid (APH) and 3-[2-carboxypiperazin-4-yl]-propyl-1-phosphonate (CPP), and two non-competitive NMDA antagonists, phencyclidine (PCP) and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801), were compared in 4 models of induced seizures in mice. All 4 drugs protected against tonic extensor seizures induced by pentylenetetrazol (PTZ), by submaximal (15 mA) electroconvulsive shock (ECS) and by maximal (50 mA) ECS. Similar orders of potency (i.e., MK-801 greater than PCP greater than or equal to CPP greater than APH) were seen in each of the 3 seizure models. All 4 drugs failed to block clonic seizures induced by picrotoxin in the dose ranges that protected from tonic seizures. These data are consistent with other data demonstrating that competitive and non-competitive NMDA antagonists have similar pharmacologic effects. These results also support the suggestion that the anticonvulsant effects of competitive and non-competitive NMDA antagonists are mediated by the NMDA receptor-ionophore complex.

2-Amino-5-phosphonovalerate↗
PubMed1992

Intracerebroventricular application of competitive and non-competitive NMDA antagonists induce similar effects upon rat hippocampal electroencephalogram and local cerebral glucose utilization.

In this study we have used electrophysiological and metabolic markers to investigate the effects of competitive and non-competitive NMDA antagonists in rats after central or peripheral administration. The non-competitive antagonist, MK-801, induced dose-dependent suppression of rat hippocampal EEG energy both after intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) application. Similar effects were observed after i.p. and i.c.v. application of the competitive antagonist, DL-CPP-ene. Whereas the MK-801 was more potent after i.p. application, DL-CPP-ene was more potent after i.c.v. administration. Intracerebroventricular administration of MK-801 and DL-CPP-ene resulted in similar changes in the pattern of local cerebral glucose utilization in the olfactory tubercle and regions of the limbic system such as the anteroventral thalamus, hippocampus and entorhinal cortex. Intravenous (i.v.) administration of MK-801 induced increases in glucose metabolism similar to those observed after i.c.v. application. In contrast, i.v. administration of DL-CPP-ene induced only small decreases of glucose utilization in several regions of the central sensory system. Thus the blockade of glutamatergic (NMDA) transmission results in decreased hippocampal EEG activity which is paralleled by increased metabolic activity in this area. We conclude from EEG recordings and [14C]2-deoxyglucose uptake experiments that both non-competitive and competitive NMDA antagonists produce the same pattern of alterations after i.c.v. administration. Apparent differences in efficacy after peripheral administration may be largely due to differences in bioavailability.

Animals↗
PubMed1992

Differential behavioural and neurochemical effects of competitive and non-competitive NMDA receptor antagonists in rats.

The behavioural and biochemical effects of the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, dizocilpine and memantine, and the competitive NMDA receptor antagonist, CGP 39551, were investigated in rats. Systemic injections of dizocilpine (0.33 mg/kg) increased locomotion and rearing in an open field, whereas memantine (20 mg/kg) increased only locomotor activity. CGP 39551 (10 and 20 mg/kg) did not change open field activity. Dopamine (DA) metabolism--as measured by the ratio of dihydroxyphenylacetic acid/dopamine (DOPAC/DA)--increased in response to dizocilpine in the prefrontal cortex and the nucleus accumbens. Memantine enhanced DOPAC/DA in the prefrontal cortex, the nucleus accumbens and to a lesser degree in the posterior striatum. In contrast to non-competitive NMDA receptor antagonists, CGP 39551 did not increase DA metabolism of subcortical structures and even decreased DOPAC/DA in the prefrontal cortex. These results indicate that competitive and non-competitive NMDA receptor antagonists affect spontaneous locomotion differentially in rats. The biochemical data imply that the stimulant actions non-competitive NMDA receptor antagonists are at least partially due to activation of ascending dopaminergic systems. Potential mechanisms involved in the differential effects of both types of NMDA receptor antagonists are discussed.

2-Amino-5-phosphonovalerate↗
PubMed1996

Competitive and non-competitive NMDA receptor antagonists induce c-Fos expression in the rat anterior, cingulate cortex.

In the present study we tried to find out whether the competitive NMDA receptor antagonist CGP 40116 was capable of inducing c-Fos expression in the rat cingulate cortex in a manner similar to that described previously for the non-competitive NMDA receptor antagonist MK-801. Induction of fast early genes by MK-801, especially in the rat cortex, has recently been linked with the neurotoxic effects of non-competitive NMDA receptor antagonists on cortical neurones, hence it was of interest to extend those studies to another class of NMDA receptors antagonists i.e., competitive one. It was found that CGP 40116 (2.5 and 5 mg/kg) induced c-Fos expression in the rat anterior cingulate cortex. That effect was dose-dependent and was shown as an increase in the number of cells expressing the c-Fos immunoreactivity. A qualitatively similar, but quantitatively stronger, effect was observed after administration of MK-801 (0.2 and 0.4 mg/kg), which also caused a dose-dependent increase in the number of c-Fos positive neurones. The described dose-dependent effects of CGP 40116 and MK-801 are shown as an increase in the number of c-Fos-positive neurones, but not as an increase in the optical density of c-Fos immunostaining in c-Fos positive neurones. In control, vehicle-injected rats, the constitutive c-Fos immunoreactivity was not found in the rat anterior cingulate cortex. The obtained data indicate that both competitive and non-competitive NMDA receptor antagonists may induce similar effects on the c-Fos immunoreactivity in the rat anterior cingulate cortex, and that their administration may lead to similar functional consequences resulting form activation of fast, early genes.

2-Amino-5-phosphonovalerate↗
PubMed2002

Is healthy competition healthy? New evidence of the impact of hospital competition.

Competition among hospitals is commonly regarded as inefficient due to the medical arms race phenomenon, but most evidence for this hypothesis predates the Medicare prospective payment system and preferred provider legislation. Recent studies indicate hospital competition reduces costs and prices, but nearly all such research has focused on California. We add to the body of literature that analyzes the effects of competition in hospital markets. Using data from the state of Washington, we show that hospitals assume more risk in competitive markets by being more likely to accept prospective payment arrangements with insurers. If the arrangement is retrospective, the hospital is more likely to offer a discount as the number of competing hospitals increases. Both findings indicate that competitive forces operate the same in hospital markets as in most others: as the number of competitors increases, prices decrease and market power shifts from the suppliers to purchasers. The medical arms race hypothesis that favors more concentrated hospital markets no longer appears to be valid.

Competitive Bidding↗
PubMed1996

The impact of a competitive and a non-competitive NMDA receptor antagonist on dopaminergic neurotransmission in the rat ventral tegmental area and substantia nigra.

The study compares effects of the competitive and non-competitive NMDA receptor antagonists, CGP 40116 and MK-801 respectively, on the metabolism of dopamine and on the density of D-1 and D-2 dopaminergic receptors in the rat ventral tegmental area and substantia nigra. The effects of CGP 40116 were tested in a range of doses which either were devoid of or had locomotor- or stereotypy-stimulating effects. It was found that (1) CGP 40116 given in a dose of 5 mg/kg enhanced the locomotor activity of rats and evoked a stereotypy-like activity; doses of 1.25 and 2.5 mg/kg were devoid of such effects; (2) CGP 40116 (5 mg/kg) enhanced the concentrations of dopamine, DOPAC and HVA in the ventral tegmental area, whereas the lowest dose, 1.25 mg/kg was without effect; a dose of 2.5 mg/kg increased the concentration of dopamine only; the only effect of CGP 40116 (5 mg/kg) observed in substantia nigra, was an increase in dopamine concentration; its doses of 1.25 and 2.5 mg/kg were ineffective. (3) MK-801 (0.2 and 0.4 mg/kg) enhanced the concentrations of dopamine, DOPAC and HVA in both structures. A dose of 0.1 mg/kg increased the dopamine concentration only. The effects of MK-801 in substantia nigra were quantitatively weaker than those observed in ventral tegmental area. (4) Both CGP 40116 (5 mg/kg) and MK-801 (0.4 mg/kg) evoked alterations in the density of dopaminergic receptors. D-2 receptors, were up-regulated by MK-801 in ventral tegmental area and subregions of substantia nigra, i.e. pars compacta and pars reticulata, whereas CGP 40116 evoked similar effects in ventral tegmental area only. D-1 receptors in pars compacta and pars reticulata of substantia nigra were down-regulated after administration of either drug. It is concluded that competitive NMDA receptor antagonists in doses which evoke hyperlocomotion and stereotypy-like activity, may have a substantial impact on the dopaminergic neurotransmission in the rat ventral tegmental area and substantia nigra, similar to that described for MK-801, a non-competitive NMDA receptor antagonist. The obtained results may suggest that CGP 40116 and, possibly, other competitive NMDA antagonists may have dopaminomimetic properties, and that their clinical potentials may be limited by the risk of evoking dopamine-dependent psychotomimetic and abusing effects, similar to those described for MK-801.

2-Amino-5-phosphonovalerate↗
PubMed2005

Competitive ion-exchange adsorption of proteins: competitive isotherms with controlled competitor concentration.

The competitive adsorption processes inevitably present in chromatographic separations of complex mixtures have not been extensively studied. This is partly due to the difficulty of measuring true competitive isotherms, in which all system parameters (including competitor concentrations) are held constant. We report a novel approach to determining competitive protein adsorption isotherms in which the competitor concentration is held constant across the entire isotherm. By using the heme prosthetic group in cytochrome b5 as a quantitative spectrophotometric label, competitive isotherms between cytochrome b5 and alpha-lactalbumin can be constructed. Similarly, manganese-substituted protoporphyrin IX heme replacement allows the non-perturbing labeling of individual cytochrome b5 conservative surface charge mutants by replacement of a single atom in the interior of the protein. This labeling allows the study of competition between cytochrome b5 charge mutants of identical size and shape, which differ only in charge arrangement. Using these techniques, the effect of competing species on equilibrium behavior and the apparent heterogeneity of anion-exchange adsorbents in the presence of competitors can be quantitatively studied by fitting the data to two popular single-component binding models, the Temkin and the Langmuir-Freundlich (L-F) isotherms.

Adsorption↗
PubMed1994

A new method for estimating dissociation constants of competitive and non-competitive antagonists with no prior knowledge of agonist concentrations.

1. A method is presented which enables the dissociation constant (KI) of a competitive, pseudo-irreversible or non-competitive antagonist-receptor complex to be estimated without knowledge of agonist concentrations. 2. The technique has been tested using sets of concentration-response data which simulated these various types of antagonism. 3. The points for each set of simulated data could be plotted both as agonist concentration-response curves at fixed antagonist concentrations and vice versa, producing paired data sets. 4. pKI-values were estimated from such paired data sets using appropriate graphical and computer curve-fitting methods. 5. For competitive antagonism, for each paired data set the computer curve-fitting techniques gave the same value for pKI, assuming drug-receptor interaction to be 1:1 and agonist concentrations to be known. 6. When agonist concentrations were assumed unknown, pKIS could not be estimated by the conventional method (using agonist dose-ratios) but could still be obtained (for competitive, pseudo-irreversible and non-competitive antagonism) by the new method. 7. This new method should be especially useful for measuring dissociation constants of antagonists against neuronally- or ionophoretically-released agonists. It may also be useful when agonist is applied exogenously, especially if suitable drugs are not available to block agonist uptake and/or metabolism.

Binding Sites↗