Key result
In conscious dogs with chronic heart-block, acebutolol, metoprolol, and propranolol significantly lowered ventricular rate in a dose-dependent manner, with metoprolol and acebutolol exhibiting 2 and 3 times weaker ventricular beta-blocking potency than propranolol.
Why the study?
Do acebutolol, metoprolol, and propranolol affect atrial and ventricular rates in conscious dogs with chronic heart-block?
Do acebutolol, metoprolol, and propranolol affect atrial and ventricular rates in conscious dogs with chronic heart-block?
In conscious dogs with chronic heart-block, acebutolol, metoprolol, and propranolol dose-dependently depress ventricular rate proportional to their beta-blocking potency, while acebutolol and metoprolol also increase atrial rate.
Supports differential beta-blocker potency for ventricular rate control in experimental heart block; leaves open relevance to human AV conduction disorders.
1 Atrial and ventricular chronotropic effects of acebutolol, metoprolol and propranolol were studied in conscious dogs with chronic heart-block. Ventricular beta-adrenoceptor blocking activity was assessed for the three dogs against isoprenaline (1 microgram/kg) under the same experimental conditions. 2 Acebutolol and metoprolol significantly increased atrial rate. The effect was proportional to the dose for acebutolol, independent for metoprolol. Propranolol had no significant effect on atrial rate. All three drugs significantly lowered ventricular rate in proportion to the dose. 3 Ventricular beta-blocking potencies of metoprolol and acebutolol were respectively 2 and 3 times weaker than that of propranolol as indicated by ED50 values. 4 The ventricular depressor effect observed was proportional to the degree of ventricular beta-blockade present, although this may not be the only factor involved.
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Boucher et al. (1980) studied Chronic heart-block (n=10). Acebutolol, metoprolol, and propranolol vs. Saline was evaluated on Ventricular rate reduction and ventricular beta-blocking potency. In conscious dogs with chronic heart-block, acebutolol, metoprolol, and propranolol significantly lowered ventricular rate in a dose-dependent manner, with metoprolol and acebutolol exhibiting 2 and 3 times weaker ventricular beta-blocking potency than propranolol.
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