Bioassays... highly specific

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Hello bloggers,
Sorry for the delay and I am going to give you all an idea about BIOASSAYS. Many new active ingredients are found in different species of plants which have different pharmacological properties .But do all these show equal reponse? To know the concentration of the active ingredient ASSAYS are performed.
They can be either
* Chemical: where concentration is estimated through chemical methods
* Biological: where concentration in a biological material is estimated using animal models.

Bioassays are very sensitive and specific and they are performed on whole animals or isolated tissues or even cells.

WHY ONLY BIOASSAY?
1. Certain drugs cannot be estimated chemically whose chemical composition is not known.
2. When chemical assay is too complex.
3. When drugs obtained from different sources have different compositions.
4. When active constituent is not known.
Bioassays are done either indirectly or directly.

Indirect assays: If the dose and response are compared to know the potency of the sample then it is called Indirect bioassays.
Ex. Ergot preparations cause vasoconstriction and cause blue discoloration in the comb of a leghorn cock.The intensity of blue color changes with the dose.
Direct assays:

The dose required to produce a pharmacological action is called threshold dose and this is directly measured.
The ratio of threshold dose of the sample to the threshold dose of standard is calculated and potency is determined. Like bioassay in guinea pigs.
The concentration of unknown is determined directly using methods like
Interpolation: Here log dose and response of atleast 4 standard concentrations are plotted and the unknown is read through graph.
Matching: A constant dose and response of sample is bracketed with different doses of standards till they match and thus the potency is calculated
SPECIFICITY:
Rats are used for vasopressin, mice for insulin, and rabbits for d-tubocurarine.
Reference:
R.S.Satoskar and S.D. Bhandarkar ,Revised 21stedition,Popular prakashan pivate ltd,saurabh printers.

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Gangadhar Hari's picture
Author: Gangadhar Hari

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Maanasa's picture

please guide me how to post blogs here...plzzzzz mail me bmaanasa@ymail.com

maanasa

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