Chemical methods bioassays

The measurement of the catalytic activity of an enzyme is also a bioassay despite the fact that chemical methods may be used to measure the amount of substrate of product. Although the use of radioimmunoassays may enable the determination of the molar concentration of an enzyme, the problem of the relationship between molar concentration and physiological effects still remains. 

Laboratory analyses on poisoned animals are essendally normal, except that the insecdcide is found in dssues by means of bioassay. A method for specific, quandtadve chemical analysis for chlordane is now available using small amounts of subcutaneous fat. Chronically poisoned animals show degeneradve changes in the liver and kidney tubules. 

Stimulation of the presynaptic nerve results in the release of ACh in a Ca dependent manner. Release of ACh can be demonshated using a bioassay of the type originally employed by Loewi or more commonly no adays by a direct chemical method. 

Biological assay (bioassay) is the process by which the activity of a substance (identified or unidentified) is measured on living material e.g. contraction of bronchial, uterine or vascular muscle. It is used only when chemical or physical methods are not practicable as in the case of a mixture of active substances, or of an incompletely purified preparation, or where no chemical method has been developed. The activity of a preparation is expressed relative to that of a standard preparation of the same substance. Biological standardisation is a specialised form of bioassay. It involves matching of material of unknown potency with an International or National Standard with the objective of providing a preparation for use in therapeutics and research. The results are expressed as units of a substance rather than its weight, e.g. insulin, vaccines. 

There are two different methods used to assess contamination (1) experimental measurements of contamination and (2) prediction of the possible contamination. We considered above some of the detailed predictive methods. For contamination measurements there are chemical methods and bioassays. In the first case a more detailed assessment of the composition of the contaminants is done. The clear identification of the components related to the pollution phenomenon is useful in identifying the remediation or mitigation initiatives to be adopted. However, there are limitations to the chemical approach ... 

Historically, assessment of thiamine status was by animal bioassay (the correction of bradycardia in thiamine-deficient rats) and later by microbiological assays using the fungus Phycomyces hlakesleeanus, yeast fermentation, or bacteria of the Staphylococcus, Streptococcus, or Lactobacillus species. Some bacterial microbiological assays are still in use in the food industry. Early chemical methods were often based upon the production of a fluorophore, thiochrome, when thiamine is oxidized with ferricyanide in alkaline solution, a property that is used in some modern chromatographic methods. 

In contrast a number of isolated organ preparations have been used as bioassay systems. Historically bioassay systems were developed when the nature of the chemicals themselves were often unknown and/or the sensitivity of chemical methods was insufficient to measure the extremely small concentrations of chemicals necessary to produce responses in bioassay systems. Thus, these systems could be used not only to measure the effect of the chemical on the system, but once the system was calibrated the concentration of a solution of the chemical could be determined based on the response it produced in the system. Furthermore, bioassay systems allowed for the demonstration of specific principles. For example, the desionstration by Loewi... 

Complete information on pollution available. If all contaminants present in the sample have been analysed using conventional physical or chemical methods, the application of bioassays provides further information e.g. on toxicity interactions and bioavailability. It has to be emphasised that for multiple contamination, bioassays reveal an overall combined toxicity response to the bioavailable part of each contaminant present in the mixture. The identification of the bioavailable fraction of a particular substance by relating the measured effect to the measured concentration of the chemical is only possible for a single substance contamination (only one toxic chemical present). Although it may be tempting for risk assessors, the response of multiple pollution cannot be used to calculate the bioavailable fraction (percentage of the total concentration of a compound) of a particular chemical from the mixture, unless toxicant... 

Lodhi, G.N. R. Renner D.R. Clandinin. Available carbohydrate in rapeseed meal and soybean meal as determined by chemical method and chick bioassay. J. Nutr. 1969, 99, 413 18. 

The determination of pesticide contents in water, organic substrates,. sediments, and animal tissues depends on the chemical methods. The solid materials of plant and animal tissues are homogenized and extracted with acetone or hexane, evaporated to a small volume for microdetermi-nation by various chromatographic methods. The concept of in situ bioassays is mainly based on exposure of test animals In the contaminated water and determination of... 

There are also chemical methods such as HPLC, the most widely used method after bioassays LC-MS the enzyme-inhibition assays such as protein phosphatase inhibition assays, an inexpensive technique [75,76] and the immunoassays (monoclonal antibodies to OA and DTX-1, and enzyme-linked immunoabsorbent assay). There are several commercial kits available, and the cytotoxicity assays obviate the morphological changes caused by the DSP toxin activity in various cell lines for example, human KB cells, salmon and rat hepatocytes, and cultured neurons. 

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