ACEBUTOLOL, METOPROLOL AND PROPRANOLOL IN CONSCIOUS DOGS WITH CHRONIC HEART‐BLOCK: CHRONOTROPIC EFFECTS AND RELATION BETWEEN DEPRESSION OF VENTRICULAR ACTIVITY AND β‐ADRENOCEPTOR BLOCKING POTENCY

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Abstract
1 Atrial and ventricular chronotropic effects of acebutolol, metoprolol and propranolol were studied in conscious dogs with chronic heart-block. Ventricular β-adrenoceptor blocking activity was assessed for the three drugs against isoprenaline (1 μg/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 β-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 β-blockade present, although this may not be the only factor involved.

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