Indirect action

Finally, there are also pollutants that do not cause direct health impacts hut that may have the potential to cause harm indirectly, through their actions on the overall ecology, or as they function as precursor chemicals that lead to the production of other harmful chemicals. The major indirect-action pollutants include volatile organic carbon (VOC) compounds that act as precursors to more harmful species chemicals called halocarbons and chemicals called greenhouse gases. 

MTX caused a contraction of vascular smooth muscle and positive inotropic, positive chronotropic and arrhythmogenic effects on cardiac muscle. The effect of MTX was little affected by various receptor blockers, a Na channel blocker or a catecholamine depleting agent. Further, MTX had no effect on the enzymes which were related to Ca movements, such as Na , K -ATPase, cyclic AMP phosphodiesterase, and sarcoplasmic reticulum Ca -ATPase. These results would eliminate the possible involvement of an indirect action elicited by the release of chemical mediators and direct modifications of their receptors, Na channels, or various enzymes as a major mechanism of action of MTX. 

Tyramine is produced by decarboxylation of tyrosine and is present in the CNS in higher (threefold) concentrations than m-tyramine, the hydroxylated derivative of phenylethylamine. In the periphery / -tyramine is easily hydroxylated to octopamine, which has some direct effects on ai adrenoceptors, unlike tyramine which functions by releasing NA. When tested on central neurons tyramine always produces the same effects as NA but they are slower and less marked, implying an indirect action. By contrast octopamine often produces the opposite effect to NA and it is probable that octopamine may have a functional role in the invertebrate CNS where it is found in higher concentrations (5pg/g) than in the mammalian brain (0.5ng/g). Neither tyramine nor octopamine have distinct behavioural effects, unlike phenylethylamine,... 

By indirect action of the shock wave after it has been reflected from solid surfaces in the vicinity of the explosion. 

Chemical weathering of minerals during pedogenesis can be enhanced by microbial activity by a factor as high as 106 (Kurek 2002). Microorganisms can dissolve minerals by direct and indirect actions under aerobic and anaerobic conditions (Robert and Berthelin 1986 Ehrlich 2002 Kurek 2002). In some cases of attack, the microorganisms may be dispersed in the soil solution in others, they may grow in biofilms on the surface of susceptible minerals. 

Quinn JM, Itoh K, Udagawa N, Hausler K, Yasuda H, Shima N, Mizuno A, Higashio K, Takahashi N, Suda T, Martin TJ, Gillespie MT (2001) Transforming growth factor beta affects osteoclast differentiation via direct and indirect actions. J Bone Miner Res 16 1787-1794... 

All of the stimulants discussed have some potential for abuse, varying with environmental factors, context of use, and individual predispositions. Still, pharmacology plays a major causal role drugs with direct or indirect actions on dopamine systems are more likely to be used compulsively. Stimulants have important roles in the cultures that use them. Whether used for positive or negative purposes, it is likely that our relationships with stimulant plants will long continue. 

There is no doubt that cerebral lipids, and EEA-derived LC-PUFAs in particular, have significant direct and indirect actions on cerebral function. Not only does the lipid composition of neural membranes affect the function of their embedded proteins, but also many LC-PUFAs are converted to neurally active substances. There is good evidence that psychiatric illness is associated with depletion of EFAs and, crucially, that supplementation can result in clinical amelioration. Ar well as challenging traditional views of aetiology and therapeutics in psychiatry, the clinical trial data may herald a simple, safe and effective adjunct to our standard treatments for many disabling conditions. 

RDMs and 2-HRDMs. This may be due to the fact that the different spin-blocks of these matrices are forced to contract correctly and therefore an indirect action on the spin components of the 2-G matrix may occur. On the other hand, the correction of the negativity of the spin components of the 2-G matrix in the AV purification procedure is carried out still more effectively than the negativity correction of the 2-RDM and 2-HRDM. This is illustrated for Li2 and BeH2 molecules in Table VII. The conditions imposed on the spin components of the 2-G and their contractions are essential for the N- and 5-representability of this matrix and, hence, for those of the 2-RDM and 2-HRDM. 

Practically every examined substance of mixed action has indirect action (such as that of tyramine), in addition to a direct action (activation of adrenoreceptors), and aU are a- and j3-adrenomimetics of indirect (mediated) action. 

Metaraminol is a sympathomimetic amine of both direct and indirect action that has hemodynamic characteristics similar to norepinephrine. It has the ability to elevate both systohc and diastolic blood pressure. 

The general cardiodynamic effects of cardiac glycosides are quite complex because of the combination of their direct action on the heart and indirect action, which changes the electrophysiological properties of the heart (automatism, conductivity, and excitability). 

Although indirect and probably quite rare, another route has been reported for allelochemical interference with plant-water relationships. Lovett and Duffield (47) identified benzylamine as an allelochemical in the leaf washings from the cruciferous weed Cametina sativa (L.) Crantz. Subsequent work showed benzylamine induced hydrophobic conditions in the soil, and these conditions could reduce water availability for plant growth (48). Thus, indirect action through changes in soil structure could be partially responsible for adverse effects on linseed (Linseed usitatissimm L.) and could enhance more direct allelopathic effects. 

Such unspecific oxidative attack is also discussed as a possible route in the biodegradation fate of PVA. Oxidation of PVA should be possible, as very aggressive oxidative species can be generated by the extracellular enzyme mixtures of wood-rotting fungi. Unspecific oxidative incidents are to be expected when strongly oxidising low molecular mediators react with PVA, a mechanism that is described as the indirect action of laccase enzymes [77]. Reports about the beneficial... 

Ephedrine is a naturally occurring alkaloid that can cross the blood-brain barrier and thus exert a strong CNS-stim-ulating effect in addition to its peripheral actions. The latter effects are primarily due to its indirect actions and depend largely on the release of norepinephrine. However, ephedrine may cause some direct receptor stimulation, particularly in its bronchodilating effects. Because it resists metabolism by both COMT and MAO, its duration of action is longer than that of norepinephrine. As is the case with aU indirectly acting adrenomimetic amines,... 

Both the direct and indirect actions of quinidine are important in determining its ultimate effect on A-V conduction. The indirect (anticholinergic) properties of quinidine prevent both vagally mediated prolongation of the A-V node refractory period and depression of conduction velocity these effects lead to enhancement of A-V transmission. Quinidine s direct electrophysiological actions on the A-V node are to decrease conduction velocity and increase the ERP. 

The effects of disopyramide on the myocardium and specialized conduction tissue (Table 16.2) are a composite of its direct actions on cardiac tissue and its indirect actions mediated by competitive blockade of muscarinic cholinergic receptors. 

The net effects of bretylium on the electrical and mechanical properties of the heart are a composite of the direct actions of the drug on cardiac tissues and indirect actions mediated through the drug s effects on the sympathetic nervous system. 

Chemical and biological effects of ionizing radiation are thought to occur through two main mechanisms direct interaction of the radiation with food components and living cells in materials exposed to it, and indirect action from radiolytic products, such as the radicals formed from water molecules (see Chap. 12). 

Psvchopharmaceutieals are medications that can affect the behavior and subjective state of man and are used therapeutically on account of these psychotropic effects. Apart from psychopharmaceuticals, there are man) other substances with psychotropic action, such as alcohol, nicotine, cocaine and heroin, which are characterized as social or addictive products and have no generally recognized therapeutic applications in Western medicine. Analgesics and members of other drug classes also have direct or indirect actions on subjective state and behavior but are not considered to be psychopharmaceuticals because they are not used primarily for their psychotropic effects. 

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