Saturday 12 May 2012

Bioassay of digitalis

Bioassay of digitalis
Principle: Potency of the test sample is compared with that of the standard preparation by
determining the action on the cardiac muscle. Any other equivalent method, which gives
results similar to those obtained by this method as also valid.



Standard Preparation and Units: The standard preparation is a mixure of dried and
powdered digitalis leaves (1 unit = 76 mg.)

Preparation of Extracts: Exact amount of the powder is extracted with dehydrated
alcohol in a continuous extraction apparatus for six hours. The final extract should
contain 10 ml. (5 ml. alcohol + 5 ml. water) per 10 g. of digitalis powder. It should be
stored in between 5
oC and –5
oC.

1. Guinea–pig Method (End point method) : Standard and test sample extracts are
diluted with normal saline in such a way that 1 g of digitalis powder is diluted to 80 ml.
A guinea pig is anaesthetized with a suitable anaesthetic. It is dissected on the operation
table. The jugular vein is traced out by removing adhering tissues and cannulated by
means of venous cannula. A pin is inserted in the heart, such that it gets inserted in the
apex of the heart. In this way, we can observe the heart beats by up and down movements
of the pin. The injection is continued through venous cannula untill the heart is arrested in
systole. The amount of extract required to produce this effect is taken as the lethal dose of
the extract. Another set of 19 animals of the same species are used for this experiment
and the average lethal dose is determined. It is not necessary to determine the lethal dose
of the std. during each time of the experiment. But it should be occasionally checked.

The lethal dose of the test sample is determined in a similar way using minimum 6
guinea–pigs of the same strain.

The potency of the test sample is calculated in relation to that of the std. preparation by
dividing the average lethal dose of the sample to the test and expressed as units per gram.

132. Pigeon Method: Minimum 6 pigeons are used for testing each sample. They should be
free from gross evidence of disease or emaciation. The weight of the heaviest pigeon
should not exceed twice the weight of the lightest pigeon. Food is withheld 16-28 hours
before the experiment. Pigeons are divided on the basis of their sex, weight and breed,
into two groups. They are anaesthetized with anaesthetic ether.

One side of the wing is dissected and the alar vein is cannulated by means of a venous
cannula. Dilutions are made with normal saline. Average lethal dose of each sample is
determined; results are tabulated and calculated as per guinea pig method. The lethal dose
per kg. of body weight is determined for each pigeon. The potency of the test sample is
determined by dividing the mean lethal dose of standard by the mean lethal dose of the
test sample.

In pigeons, stoppage of heart is associated with a characteristic vomiting response called
‘emesis’. The milk from the crop sac of pigeons is being ejected out. This may be taken
as the end point response of digitalis.

14 comments:

Unknown said...

A GOOD MATERIAL FOR BIOASSAYS

Unknown said...
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Unknown said...

Very informative and easily understandable method

uuuuu said...
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uuuuu said...
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uuuuu said...
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uuuuu said...
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Unknown said...

Good material for bioassay

Unknown said...

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Unknown said...

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