Abstract
1. 4-Hydroxypropranolol, a metabolite produced after oral administration of propranolol, has been shown to be a β-adrenoceptor blocking drug. It is of similar potency to propranolol in antagonizing the effects of isoprenaline on heart rate and blood pressure in cats and against isoprenaline protection of guinea-pigs from bronchospasm. It is not cardioselective.
2. In rats depleted of catecholamine 4-hydroxypropranolol produced an increase in heart rate, suggesting that it has intrinsic sympathomimetic activity.
3. In anaesthetized dogs 4-hydroxypropranolol produced a decrease in heart rate and dP/dt and an increase in A-V conduction time at doses within the range 0·09-1·25 mg/kg. These effects are a result of β-adrenoceptor blockade. In dogs depleted of catecholamines these same doses produced an increase in heart rate and dP/dt and a decrease in A-V conduction time. These responses were antagonized by propranolol, and were due to the intrinsic sympathomimetic activity of the compound. At higher doses (5·25 and 13·25 mg/kg) a further dose dependent decrease in heart rate and dP/dt and an increase in A-V conduction time occurred. This trend was also seen in animals depleted of catecholamines. These changes represent membrane stabilizing activity of 4-hydroxypropranolol.
4. 4-Hydroxypropranolol is a potent β-adrenoceptor blocking drug with both intrinsic sympathomimetic activity and membrane stabilizing activity.
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Selected References
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