Shah Nawaz, Jalal -ud- Din, Qazi Rashid Ahmed, Tahir Saleem Khan, Muhammad Jan


Background: Propranolol is a non-selective, while acebutolol is a cardioselective beta blocker. This study was
designed to implore into the effect of nonselective and cardioselective beta blockers on the electrically stimulated
contractile response of isolated diaphragm of rat. Methods: Study was conducted on male and female rats of albino
variety, weighing 150-200 grams, in Jinnah Postgraduate Medical Centre Karachi. Diaphragmatic strips were
prepared. Tissue was transferred to a tissue bath containing oxygenated Krebs solution kept at 32°C. One end of the
strip was connected to the electrodes of an electric stimulator, while its other end was connected to a polygraph through
a force displacement transducer. Normal recordings of the response of tissue to electrical stimulation was obtained.
The response was observed with 10-8 – 10-3 M concentrations of propranolol and acebutolol separately and in series.
Contractile response of the tissue was measured in millimeters. Arithmetic mean for each set of observation was
T test was performed and P value was determined from the t table Results: Both propranolol and acebutolol produced
significant depression of the contraction of rat isolated diaphragm as a result of electrical stimulation. Conclusion:
Our study has shown that the depressant effect of beta adrenoceptor blocking drugs. perhaps, do not play important
role in the etiology of respiratory distress produced by these drugs, because the depressant effect of both propranolol
and acebutolol on diaphragm are only produced in high doses.


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