Chagasic IgG binds and interacts with cardiac beta adrenoceptor-coupled adenylate cyclase system

It has been previously shown that sera from chagasic patients have an antibody specific for beta adrenoceptors, independently of other tissue-reactive antibodies as the EVI (endocardium, blood vessels, interstitium) system, and it is highly specific to other heart diseases. In this paper we demonstrate that the IgG present in chagasic sera was able to bind to beta adrenoceptors of the heart and also to interact with the membrane bound adenylate cyclase complex, inducing stimulation of enzymatic activity. Moreover, this antibody stimulated contractile activity of guinea pig myocardium, that could be blocked by a specific beta adrenoceptor antagonist. Chagasic IgG inhibited the binding of (-)-(3H)-dyhidroalprenolol to a beta-adrenergic receptor of purified guinea pig myocardial membranes behaving as non-competitive inhibitor. This IgG also exerted a non-competitive inhibition upon the mechanical effect of exogenous norepinephrine.