This document discusses screening methods for evaluating bronchodilators. It describes 5 main methods: [1] measuring excess air volume in anesthetized guinea pigs to quantify bronchospasm, [2] evaluating the effects of spasmogens like arachidonic acid on respiratory function in vivo, [3] measuring time until convulsions after histamine inhalation to assess bronchial hyperreactivity, [4] using body plethysmography to measure respiratory parameters after histamine-induced bronchoconstriction, and [5] using pneumotachography to evaluate respiratory effects in anesthetized guinea pigs.

1. Screening Methods of
Bronchodilators
Guided By: Presented By:
Mr. Rupesh Gautam Prafulla Chandra Tiwari
Senior Lecturer, Dept. of Pharmacology M.Pharm Pharmacology
Jaipur College of Pharmacy Jaipur College of Pharmacy
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2. Bronchodilators
The pharmacological therapy of asthma employs
drugs aimed more directly at decreasing
bronchospasm (i.e., bronchodilators).
The main drugs used as bronchodilators are β2-
adrenoceptor agonists; others include xanthines,
cysteinyl leukotriene receptor antagonists and
muscarinic receptor antagonists.
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3. β2 Adrenergic Receptor Agonists
 The β adrenergic receptor agonists available for the
treatment of asthma are selective for the β2 -receptor
subtype.
 The mechanism of the antiasthmatic action of β2
adrenergic receptor agonists the direct relaxation of
airway smooth muscle and consequent bronchodilation
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4. Theophylline
• It inhibits phosphodiesterase and blocks adenosine
receptors.
• Theophylline has a narrow therapeutic window:
unwanted effects include cardiac dysrhythmia,
seizures and gastrointestinal disturbances.
• It is given intravenously (by slow infusion) for
status asthmaticus, or orally (as a sustained-release
preparation) as add-on therapy to inhaled
corticosteroids and long-acting β2 agonists
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5. Screening Models of Bronchodilators
1.Bronchospasmolytic activity in anesthetized guinea
pigs (Konzett-Rössler method)
2. Effect of arachidonic acid or PAF on respiratory
function in vivo
3. Bronchial hyperreactivity
4.Body plethysmography and respiratory parameters
after histamine-induced bronchoconstriction in
anesthetized guinea pigs.
5. Pneumotachography in anesthetized guinea pigs
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6. Bronchospasmolytic activity in anesthetized
guinea pigs (Konzett-Rössler method)
PURPOSE AND RATIONALE:
•The method is based on registration of air volume changes of a
living animal in a closed system consisting of the respiration
pump.
•Bronchospasm decreases the volume of inspired air and increases
the volume of excess air.
•Thus, the degree of bronchospasm can be quantified by recording
the volume of
excess air.

7. Procedure:
•Guinea-pigs of either sex weighing 250–500 g are
anaesthetized with 1.25 g/kg i.p. urethane.
•The trachea is cannulated by means of a two way cannula,
one arm of which is connected to the respiratory pump and
the other to a Statham P23 Db transducer.
•The animal is artificially respired using a Starling pump
with an inspiratory pressure set at 90–120 mm of water, an
adequate tidal volume of 3 ml/100 g body weight and a
frequency of 60 strokes per minute.
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8. •Excess air, not taken up by the lungs, is
measured and recorded on a polygraph
• The internal jugular vein is cannulated
for the administration of spasmogens and
test compounds.
• The carotid artery is cannulated for
measuring blood pressure.
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9. Effect of arachidonic acid or PAF on
respiratory function in vivo
PURPOSE AND RATIONALE:
The test allows to evaluate the sites of action of drugs,
which interfere with the mechanisms of broncho-
constriction and thrombocytopenia; in an in vivo-
model guinea pigs are challenged with the spasmogens
and platelet-aggregating substances arachidonic acid
or PAF (platelet activating factor).

10. Procedure:
1.Male guinea pigs (Pirbright White) weighing 300–600 g are
anesthetized with 60 mg/kg pentobarbital sodium (i.p.).
2. One of the jugular veins is cannulated for the administration
of spasmogen and test compound.
3. Both external carotid arteries are cannulated; one is connected
to a pressure transducer to register blood pressure, the other is
used for blood withdrawal.
4.The trachea is connected to a Starling pump with an
inspiratory pressure set of 80 mm H2O, an adequate tidal volume
of approx. 10 ml/kg body weight and a frequency of 70–75
strokes/ min.

11. 5. Spontaneous respiration is inhibited by intravenous injection
of pancuronium (4 mg/kg) or gallamine (2 mg/kg) on time.
6. In some experiments, pulmonal ß-receptors are blocked by
intraperitoneal administration of propranolol (2 mg/kg).
7. Excess air, not taken up by the lungs, is conducted to a
transducer with bronchotimer, which translates changes in air
flow to an electrical signal.
8. Changes in air flow and arterial blood pressure are recorded
continuously.

12. Bronchial hyper reactivity
PURPOSE AND RATIONALE:
• Symptoms like asphyctic convulsions resembling bronchial
asthma in patients can be induced by inhalation of histamine or
other bronchospasm inducing agents in guinea pigs.
•The challenging agents are applied as aerosols produced by an
ultra-sound nebulizer
• The first symptoms are increased breathing frequency, forced
inspiration, and finally asphyctic convulsions.

13. •The occurrence of these symptoms can be delayed by
antagonistic drugs.
• Pre-convulsion time, i.e. time until asphyctic
convulsions, can be measured.

14. PROCEDURE
•Ten male albino guinea pigs weighing 300–400 g per
group are used. The inhalation cages consist of 3
boxes each ventilated with an air flow of 1.5 l/min.
• The animal is placed into box A to which the test
drug or the standard is applied using an ultra-sound
nebulizer.
•Alternatively, the animal is treated orally or
subcutaneously with the test drug or the standard.

15. Box B serves as a sluice through which the animal is
passed into box C.
There, the guinea pig is exposed to an aerosol of a 0.1%
solution of histamine hydrochloride provided by an
ultra-sound nebulizer.
Time until appearance of asphyctic convulsions is
measured. Then, the animal is immediately withdrawn
from the the inhalation box. The aerosols are removed
from the back wall of the boxes by applying
low pressure.

16. Bibliography:
1.Goodman Gilman, Pharmacological Basis of
Therapeutics,11th Edition. Published by Mc-Graw Hill.
2.Vogel H. Gerhard, “Drug Discovery and Evaluation”,
Second Edition, Published by Springer. Page No. 359-
368.
3.Kagoshima M, Tomomatsu N, Iwahisha Y, Yamaguchi
S, Matsuura(1997) Suppressive effects of Y-24180, a
receptor antagonist to platelet activating factor (PAF),
on antigen-induced asthmatic responses in guinea pigs.
Inflamm Res 46:147–153.