Modification of sarcolemmal enzymes by chagasic IgG and its effect on cardiac contractility.

It has been shown that sera from chagasic patients contain an antibody which binds to beta-adrenoceptors of myocardium and modulates their activity. Chagasic IgG triggered a marked stimulation of myocardial contractility with an increase in intramyocardial cyclic AMP and inhibition of (Na+ + K+)-ATPase activity. Both the mechanical and enzymatic effects of the IgG could be prevented by beta-adrenoceptor blockade or after the absorption of chagasic IgG with turkey red blood cells. In contrast, guinea pig red blood cells were unable to remove the beta-reactivity of chagasic IgG. These findings suggest that the IgG from chagasic patients increases myocardial contractility by behaving as a beta-agonist. This effect is likely related to stimulation of the adenylate cyclase coupled to the cardiac beta-adrenoceptor.