Metabolism rate-concentration relationship

Just as qualitative judgments of toxicity are made using a reference point on the metabolism rate-concentration relationship, quantitative evaluation of toxicity is also made with respect to a reference point. It would seem that the definition of the point of reference for quantitative evaluation should be more exact than that used for qualitative judgment. Unfortunately, this is not the case for waste treatment system studies. In virtually all quantitative toxicity studies, the performance of units containing added quantities of the substance under study is compared with the performance of a control unit. Invariably, the control unit is one which exhibits satisfactory biological activity and to which none of the substance under study has been added. Very rarely is the concentration of the substance under study established or fixed in the control. 

Many studies predicting metabolism have concentrated on quantitative aspects (e.g., relating the rate characteristics or proportion of a particular metabolic reaction to the experimental or calculated properties of a molecule), or the characterization of the structural requirements (i.e., structure-metabolism relationship for a particular enzyme or class of enzyme). 

By simultaneous monitoring of tidal volume and respiratory rate, or minute volume, and the concentration of an inhaled vapor in the bloodstream and the vapor in the exposure atmosphere, pharmacokinetic studies on the C t relationship have shown that the effective dose was nearly proportional to the exposure concentration for vapors such as 1,1,1-trichloroethane (Dallas et al., 1986), which has a saturable metabolism, found that the steady-state plasma concentrations were disproportion-ally greater at higher exposure concentrations. 

As a result of the highly reduced state of petroleum hydrocarbons, the preferred and most thermodynamically terminal electron acceptor for microbial processes is oxygen. The inverse relationship between the concentrations of BTEX and dissolved oxygen within a plume is indicative of the extent of microbial metabolism of this class of contaminant. Data from various sites indicate that the natural attenuation of BTEX proceeds at higher rates under oxygenated conditions. The biodegradation of... 

Structure-activity relationships are generally applied in the pharmaceutical sciences to drug molecules. The value of any structure-activity correlation is determined by the precision of the biological data. So it is with studies of the interaction of nonionic surfactants and biomembranes. Analysis of results is complicated by the difficulty in obtaining data in which one can discern small differences in the activity of closely related compounds, due to i) biological variability in tissues and animals, ii) potential differential metabolism of the surfactants in a homologous series (2), iii) kinetic and dynamic factors such as different rates of absorption of members of the surfactant homologous series (2) and iv) the typically biphasic concentration dependency of nonionic surfactant action (3 ). 

Single-dose pharmacokinetics including relationship among dose and plasma concentration, absorption rate, total, metabolic and renal clearance, volume of distribution, elimination rate constant and half-life... 

Much has been published on the extrapolation of in vivo data from animals to humans. These include pharmacokinetic data (e.g. half-lives, plasma concentrations, clearances and rates of metabolism) and pharmacodynamic data (e.g. effective and toxic doses). Two excellent reviews present many examples and insightful discussions on isometric and allometric relationships, time scales, interspecies pharmacokinetic and pharmacodynamic scaling, and physiological models (Boxenbaum and D Souza, 1990 Chappell and Mordenti, 1991). 

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