Chronotropic effects of pindolol. Relation between ventricular effects and control resting ventricular rate values in conscious dogs with chronic A-V block.

The chronotropic effects of pindolol were studied in the conscious dog with chronic A-V block. Pindolol significantly increased atrial rate, probably through both its strong intrinsic sympathomimetic activity and reflex withdrawal of atrial vagal tone in response to its hypotensive effect. Pindolol did not alter ventricular rate overall. However, in individual dogs, pindolol caused ventricular chronotropic effects that were inversely related to resting ventricular rate: it increased ventricular rate when the resting ventricular rate was low and reduced it when it was high. In view of the fact that pindolol is a beta-adrenoceptor antagonist endowed with a strong intrinsic sympathomimetic activity, this finding contributes to a better understanding of how pindolol affects heart rate.