Frequency response

Food Toxicology 2(2+0)
Lesson 4 : General Principles of Toxicology

Frequency response

If a chemical is capable of producing a response (such as death), and the response is quantitated, not all members of the group will respond to the same dose in an identical manner. What was considered as an all-or-none response applies only to a single member of the test group and is actually found to be a graded response when viewed with respect to the entire group. Such deviations in the response of apparently uniform populations to a given concentration of the chemical are generally ascribed to result from biological variation.

The frequency–response curve plots identical response vs. dose (quantal response curve) and represents the range of doses required to produce a quantitatively identical response in a large population of test subjects.

  • Explanation; in response to a toxicant, biological variation within members of a species is usually low compared with variation between species. The species population differences reflect metabolic or biochemical variations within the species itself. Testing a toxicant’s effect on a homogeneous animal population eliminates the potential causes of high variation that might occur in a heterogeneous population, if gender and age are controlled. Homogeneity of test subjects allows for valid comparisons between members of a population, and they share common characteristics. Thus, toxicity studies often use inbred strains of rodents or organisms.
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Last modified: Monday, 26 March 2012, 1:42 PM