Beta-2 adrenoceptor-mediated effects on sinus rate and atrial and ventricular contractility on isolated, blood-perfused dog heart preparations.

Changes in the sinus rate, right atrial contractile force and left ventricular contractile force in response to isoproterenol, epinephrine, dobutamine, salbutamol and procaterol were studied in isolated, blood-perfused right atrial or left ventricular cardiac preparations of the dog. Each substance elicited dose-dependent increases in the three parameters and the ranking of the potency (ED50) for each effect was isoproterenol greater than epinephrine greater than dobutamine greater than or equal to salbutamol greater than or equal to procaterol. The ED50 of procaterol for changing sinus rate was lower than for altering atrial and ventricular contractile force, whereas the ED50 of dobutamine for changing sinus rate was higher. Ranking on the basis of the ratio of increase in sinus rate to increase in atrial tension induced by the agonists gave the following order: procaterol greater than or equal to salbutamol greater than epinephrine greater than or equal to isoproterenol greater than dobutamine. Procaterol-induced increases in sinus rate and atrial contractile force were dose-dependently inhibited by the beta-2 adrenoceptor antagonist, ICI 118,551, but only attenuated slightly by the beta-1 antagonist, atenolol. On the other hand, the positive chrono- and inotropic effects on the right atrium induced by dobutamine and isoproterenol were blocked completely by atenolol. The epinephrine- or salbutamol-induced positive chrono- and inotropic responses in the right atrium were inhibited moderately by both antagonists, but ICI 118,551 inhibited sinus rate increases more effectively than the atrial tension increases.(ABSTRACT TRUNCATED AT 250 WORDS)