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PubMed1978

Competitive inhibition of specific steroid-protein binding: practical use of relative competition ratios for the derivation of equilibrium inhibition constants.

The relative competition ratio (RCR) is widely used to express the relative affinities of inhibitor(s) and agonist for a binding protein. The RCR is not a constant; it depends on the concentrations of binding sites and of radioactive hormone, and on the presence of nonsaturable binding component(s). According to the assay conditions used, equating the RCR value to the ratio Ka/Ki of the equilibrium association constants of agonist and inhibitor can lead to large errors. In the case of homogeneous non-interacting binding sites, simple correction factors permit one to calculate the ratio Ka/Ki from the measured RCR value. Calculations are given for the eventual contribution of nonsaturable binding components. Corrections can be unnecessary under well defined experimental conditions, where the bound fraction of hormone in absence of competitor is reduced by using a large dilution of binding protein and/or an increased concentration of radioactive hormone.

Binding, Competitive↗

PubMed2001

Managed competition for the poor or poorly managed competition? Lessons from the Colombian health reform experience.

BACKGROUND: In 1993, Colombia enacted and subsequently implemented a radical reform in its system of providing health care for the poor, moving in a short time from a traditional model of providing health services in public hospitals to a managed competition model in which the government buys health insurance for the poor. This study examines and attempts to draw lessons from the early experience with this reform. METHODS: Information was gathered from document reviews and interviews with key actors at both the national and local levels. Other quantitative data, such as data from existing national surveys and financial operating data, were also used as available. RESULTS: The new system made important achievements in its first few years, including the enrollment of 7 million Colombians (about half of the targeted population) in health insurance plans and improving access to care. Nevertheless, there were substantial problems with the lack of managerial infrastructure and flow of information needed for the new system to function properly. Because of these difficulties, substantial resources were wasted, and insurance coverage did not always result in true access to health care. CONCLUSIONS: Other countries contemplating similar reforms should educate health administrators and the public, and establish solid administrative capacity in advance of implementation. In Colombia, many initial problems still need to be overcome while maintaining and extending the programme's important accomplishments.

Colombia↗

PubMed2002

Selection for restraint in competitive ability in spatial competition systems.

The absence of 'super competitors' in nature is usually attributed to organisms facing trade-offs in resource allocation. Here we identify another mechanism, dependent on indirect interactions among species and non-random spatial organization, in which selection favours restraint in competitive ability. In simple spatial models of a three-species intransitive network, indirect interactions favour slower growth and selection limits the difference in growth rate among species. The mechanism involves a trade-off between selection at the individual level, which selects for increased growth rate, and at the community level, which acts to limit growth rate to less than the maximum possible. If the difference in growth rates among species becomes too large, then the community becomes unstable and collapses to a monoculture of the slowest growing species. The mechanism requires both the intransitive network structure and self-organized spatial structure in the system. Similar behaviours arise in more complex systems of more than three species, and where there are reversals in interaction outcomes between species pairs. The work suggests that spatial self-structuring, indirect interactions and selection acting on community properties can be important in evolution. It provides a partial explanation of the high level of species coexistence and apparent restraint in interspecific interactions evident in some assemblages of sessile marine colonial organisms.

Animals↗

PubMed1976

Competition by 24,25-dihydroxycholecalciferol in the competitive protein binding radioassay of 25-hydroxycalciferol.

24,25-dihydroxycholecalciferol (24,25-(OH)2D3) is equipotent to 25-hydroxycholecalciferol in the displacement of 3H25-OHD3 from rat serum binding sites, and is extracted by the ethanol procedure recommended in non-chromatographic competitive protein binding radioassays for 25-OHD. Serum 24,25-(OH)2D content was measured following 24,25-(OH)2D3 isolation from lipid extracts by liquid-gel partition chromatography. Since normal serum 24,25-(OH)2D concentration is appreciable, non-chromatographic 25-OHD assays most probably overestimate serum 25-OHD levels as a result of their recognition of 24,25-(OH)2D3.

Animals↗

PubMed1992

Observations on the conformational changes in the structure of a cell surface protease, followed by its ability to be recognised by competitive and non-competitive inhibitors.

Lung tumour cells possess a cell surface protease which can be inhibited by a cytoplasmic protein inhibitor extracted from these cells. The dissociation of this enzyme-inhibitor complex on the surface of tumour cells in sections treated with 10(-4) M sodium dodecyl sulphate has been studied. The dissociation of the inhibitor and regain of enzymic activity was followed by the use of a fluorescent probe which binds to the active centre of the cell surface enzyme in a competitive manner.

Aminacrine↗

PubMed1988

[Work prohibition or prevention of competition? Various marginal legal notes concerning the legality of a competition stipulation contracted with a (generally female) veterinarian married to a veterinarian].

With reference to legal principles such as freedom of contract and freedom of labour, it is examined whether a non-restraint of trade agreed upon with a (female) veterinary surgeon married to a veterinarian is legally operative in view of the fact that this contract in restraint of trade is not based on any legal relationship. This leads to the conclusion that arguments may be advanced, which cast doubt on the legality of these contracts. This does not imply that now the cause is open to the free setting up of a practice by the veterinarian married to a veterinary surgeon. It is briefly stated for which reasons possible competition may be unlawful in this case, so that the veterinarian will be liable in damages when damage has been sustained. In conclusion, attention is drawn to a number of other legal problems, bearing all these stipulations.

Career Choice↗

PubMed2004

Competitive effect versus competitive response of invasive and native wetland plant species.

Non-native plants can have adverse effects on ecosystem structure and processes by invading and out-competing native plants. I examined the hypothesis that mature plants of non-native and native species exert differential effects on the growth of conspecific and heterospecific seedlings by testing predictions that (1) invasive vegetation has a stronger suppressive effect on seedlings than does native vegetation, (2) seedlings of invasive species are better able to grow in established vegetation than are native seedlings, and (3) invasive species facilitate conspecific and inhibit heterospecific seedling growth. I measured growth rates and interaction intensities for seedlings of four species that were transplanted into five wetland monoculture types: invasive Lythrum salicaria; native L. alatum, Typha angustifolia, T. latifolia; unvegetated control. Invasive L. salicaria had the strongest suppressive effect on actual and per-individual bases, but not on a per-gram basis. Seedlings of T. latifolia were better able to grow in established vegetation than were those of L. salicaria and T. angustifolia. These results suggest that L. salicaria is not a good invader of established vegetation, but once established, it is fairly resistant to invasion. Thus, it is likely that disturbance of established vegetation facilitates invasion by L. salicaria, allowing it to compete with other species in even-aged stands where its high growth rate and consequent production of aboveground biomass confer a competitive advantage.

Biomass↗

PubMed1988

Kynurenate and FG9041 have both competitive and non-competitive antagonist actions at excitatory amino acid receptors.

The antagonist profile of kynurenate and FG9041 have been characterised in a modified preparation of the baby rat hemisected spinal cord. Both kynurenate and FG9041 were competitive antagonists of responses to kainate and AMPA, although neither antagonist was selective for kainate versus AMPA. In contrast, both antagonists produced an apparent unsurmountable antagonism of responses to NMDA, indicating a different mode of action at the NMDA receptor.

Animals↗

PubMed1988

Dendritic competition: competition for what?

A lesion to the retina of a newborn rat results in the retrograde degeneration of ganglion cells in a sector of retina peripheral to the lesion. The dendritic tree of ganglion cells bordering the region depleted of ganglion cells have their dendrites preferentially directed into this area. We have examined the factors which play a role in this rearrangement of the dendritic tree. The results show that the lesion in neonates selects for or produces a population of cells with the axon directed away from the depleted area and primary dendrites directed towards the depleted area. The abnormal dendritic bias cannot be accounted for solely on the basis of a decrease in contact inhibition since a reduction in the density of all ganglion cells by 30% prior to making the retinal lesion does not attenuate the abnormal dendritic bias into the depleted area. The abnormal dendritic bias is present in animals operated on up to 15 days of age postnatally but not in more mature animals. The abnormal dendritic bias develops prior to the formation of a large number of synapses in the inner nuclear layer. Our results cannot be easily accounted for by competition for synaptic contacts or a loss of contact inhibition as previously suggested. We propose that chemotropic factors produced within the area depleted of ganglion cells induce the abnormal dendritic bias and the number of synaptic contacts may limit the size of the dendritic field.

Aging↗

PubMedDate not supplied

The effect of competitive and non-competitive NMDA receptor antagonists, ACPC and MK-801 on NPY and CRF-like immunoreactivity in the rat brain amygdala.

Amygdala is the brain structure responsible for integrating all behavior connected with fear, and in this structure two neuropeptides, neuropeptide Y (NPY), corticoliberin (CRF) and the most abundant excitatory neurotransmitter glutamate seem to take part in the regulation of anxiety behavior. Our previous studies showed the modulation of NPY and CRF expression by classical neurotransmitters in some brain structures, therefore in the present study we investigated the effect of NMDA receptor antagonists on the expression of NPY and CRF immunoreactivity in the rat brain amygdala. A non-competitive NMDA receptor antagonist, MK-801, or a functional NMDA antagonist, ACPC were used. Brains were taken out and processed by immunohistochemical method using specific NPY or CRF antibodies. The staining intensity and density of IR neurons were evaluated under a microscope in amygdala sections. It was found that both MK-801 and ACPC induced a significant decrease in NPY-immunoreactivity in amygdala nerve cell bodies and terminals, which may suggest an increased release of this peptide. CRF-IR was decreased after ACPC only. The obtained results indicate that in the amygdala, the NMDA receptors mediated glutamatergic transmission may regulate NPY neurons.

Amino Acids, Cyclic↗

PubMed2004

Effect of competitive distance on energy expenditure during simulated competition.

Concepts of how athletes should expend their aerobic and anaerobic energetic reserves are generally based on results of tests where an "all out" strategy is imposed on/required from the athlete. We sought to determine how athletes spontaneously expend their energetic reserves when the only instruction was to finish the event in minimal time, as in competition. Well trained, and task habituated, road cyclists (N = 14) completed randomly ordered laboratory time trials of 500 m, 1000 m, 1500 m and 3000 m on a windload braked cycle ergometer. The pattern of aerobic and anaerobic energy use was calculated from total work accomplished and V.O (2) during the trials. The events were completed in 40.3 +/- 0.6 s, 87.4 +/- 4.1 s, 133.8 +/- 6.6 s and 296.0 +/- 7.2 s. The peak V.O (2) during the terminal 200 m of all events was similar (2.72 +/- 0.22, 3.01 +/- 0.34, 3.23 +/- 0.44 and 3.12 +/- 0.13 l x min (-1)). In all events, the initial power output and anaerobic energy use was high, and decreased to a more or less constant value over the remainder of the event. However, the subjects seemed to reserve some ability to expend energy anaerobically for a terminal acceleration which is contrary to predictions of an "all out" starting strategy. Although the total work accomplished increased with distance (23.14 +/- 4.24, 34.14 +/- 6.37, 43.54 +/- 6.12 and 78.22 +/- 8.28 kJ), the energy attributable to anaerobic sources was not significantly different between the rides (17.29 +/- 3.82, 18.68 +/- 8.51, 20.60 +/- 6.99 and 23.28 +/- 9.04 kJ). The results are consistent with the concept that athletes monitor their energetic resources and regulate their energetic output over time in a manner designed to optimize performance.

Adult↗

PubMed1975