In isolated rat atria, practolol acts as a competitive beta-adrenergic receptor antagonist with sympathomimetic properties, but lacks quinidine-like or local anesthetic activity.
Rat atrial findings on practolol's beta-antagonism with ISA but no membrane effects remain hypothesis-generating; should not inform clinical beta-blocker use.
The β‐receptor antagonism and the effects of practolol on the mechanical and electrical behaviour of isolated rat atria suspended in an organ bath have been investigated. Practolol produced a parallel shift to the right in the log. dose‐response curves of isoprenaline with no decrease in the maximal response, indicating that the antagonism is competitive. The drug was found to exert positive inotropic and chronotropic effects in doses between 10 ‐8 M and 10 ‐5 M. Practolol 10 ‐4 M did not change the threshold for excitation and the threshold for experimentally induced atrial fibrillation to any extent, neither did it prolong the effective refractory period. The results show that practolol has β‐adrenergic receptor blocking properties as well as sympatomimetic properties. The results also indicate that practolol possesses no quinidine‐like or local anaesthetic activity.
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Refsum et al. (1972) studied this question.
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