Interaction between adenosine and inotropic interventions in guinea pig atria

Isolated guinea pig atria stimulated to contract isometrically were used to determine whether adenosine at a concentration that does not cause a direct depressant effect on peak contractile force, rate of force development, and rate of relaxation was capable of influencing the elevation in these contractile parameters caused by an increase in preload, paired electrical stimulation, an increase in contraction frequency, and catecholamine stimulation in K+-depolarized and nondepolarized atrial muscle. Adenosine had no effect on the contractile parameters that were enhanced by an increase in preload or paired electrical stimulation. The nucleoside reduced the increases in the contractile parameters produced by isoproterenol stimulation, an increase in contraction frequency, and isoproterenol-induced contractions in depolarized atria. All adenosine reductions were inhibited by theophylline, an antagonist of adenosine actions. The adenosine reduction of the elevated contractile parameters caused by increasing contraction frequency was not prevented by atropine (a muscarinic antagonist) or propranolol (a beta-adrenergic blocking agent). These results suggest that adenosine at a concentration that does not produce direct negative inotropic responses is capable of attenuating the elevation in contractility elicited by catecholamine stimulation, an increase in contraction frequency, and catecholamine-induced contractions in depolarized atria. However, the reduction by adenosine of the contractile responses elicited by an increase in contraction frequency appears to be independent of catecholamines.