Immune cytokine inhibition of beta-adrenergic agonist stimulated cyclic AMP generation in cardiac myocytes

We hypothesize that reversible depression of cardiac function in cardiac allograft rejection and lymphocytic myocarditis reflects down modulation of the beta-adrenergic receptor system by a soluble product of activated immune cells. Thus, exposure of cultured cardiac myocytes to mixed lymphocyte culture or activated splenocyte supernatants produces 70% inhibition of isoproterenol-stimulated cAMP concentrations (Ki = 5% supernatant) in the absence of gross cellular injury or control media effects. This cAMP suppressive factor is not dialyzable and is ammonium sulfate precipitable. Beta-adrenergic receptor density, binding constant and affinity states are unaffected. These results demonstrate the existence of a cytokine inhibitor of cAMP accumulation that may mediate, in part, depression of cardiac contractility observed when immune cells invade the myocardium.