Exogenous exposure

The in vitro data and the results from this clinical trial were synthesized in a so-called dynamic model of receptor kinetics by Liggett [72]. According to this theory, Gly/Gly homozygous individuals are already down-regulated as a result of exposure to endogenous catecholamines. Thus, the recurring exogenous exposure to... 

If an analytic method lacks sufficient specificity, chemical interferences will result in an erroneously high reported concentration. If a measured chemical is introduced as an artifactual contaminant during sample collection or analysis, reported concentrations will also be overestimated. For example, credibly estimating human exposure to phthalates was hindered by the difficulties involved in avoiding specimen contamination with these ubiquitous chemicals the problem was resolved by focus on the much less prevalent metabolic product, the phthalate half-ester (Silva et al. 2004). Alternatively, a chemical measured as a marker of exogenous exposure may be identical with a chemical formed by an unrelated endogenous metabolic pathway. In each of those cases, a rigorous laboratory-method validation should detect the problem before data are reported. More subtly, the measured biomarker of exposure may be chemically identical with a dietary... 

The spectrophotometric methods generally compare favorably with gas chromatographic procedures at carboxy-hemoglobm concentrations greater than 2% to 3%, but their precision is poor below these levels. Therefore, they are sufficiently accurate and precise for measurement of carbon monoxide after exogenous exposure but are too insensitive to detect the increased endogenous production of carbon monoxide that occurs in hemolytic anemias. 

Bjerselius R, Lundstedt-Enkel K, Mayer I, Olsen KH (2001) Male goldfish reproductive behaviour and physiology are severely affected by exogenous exposure to 17P-estradiol. Aquat Toxicol 53 139-152... 

Evig, C.B., Kelley, E.E., Weydert, C.J., Chu, Y., Buettner, G.R., and Bums, C.P. (2004). Endogenous production and exogenous exposure to nitric oxide augment doxorubicin cytotoxicity for breast cancer cells but not cardiac myoblasts. Nitric Oxide 10,119-129. 

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