The Adrenergic Blocking Activity of Pure Beta Blockers in Comparison with Labetalol (α and β Blockers).

This study was carried out in the Laboratory of Experimental Pharmacology Allama Iqbal Medical College. Anaesthetized dogs were used as the experimental animals. Recording of the carotid arterial pressure was taken on a kymograph. Adrenaline and Isoprenaline were given in two doses each (A1, A2, I1, 12) to get their pressor and depressor responses (Control).Then the animal was injected with the drug under study in a dose of 2.5mg /kg intraveneously. The same doses A1, A2, ‘11 I were repeated in presence of the Beta Blocking drug. It was seen that Prophranolol, Timolol and Atenolol (Pure Beta receptor blockers) almost doubled the pressor response to adrenaline; whereas Labetalol (a f and Œ blocker) allowed only a minimal rise in the blood pressure. As regards depressor activity of Isoprenaline, Labetalol showed a very strong blocking effect, whereas the blockade produced by the Pure Beta Blockers, was about on third of the depressor effect.