Depressant effect of propranolol on the isolated diaphragmatic tissue of rat.

The effect of propranolol on the electric stimulation of rat isolated diaphragm shOwed the depression of its isometric force of contraction. This depressant effect of propranolol on the rat isolated diaphragm was produced in doses much higher than the doses required for the beta adrenergic receptor blocking activity. Isoprenaline showed no effect on the rat isolated diaphragm and it did not antagonise the depressant effect of propranolol on the tissue. Thus depression of the rat isolated diaphragm by propranolol is not related to its beta— receptor blocking activity and as it is propranolol at high doses, it does not seem to contribute significantly to the bronchospasm produced by the administration of propranolol (JPMA 38 183, 1988).