Right ventricular infundibular beta-adrenoceptor complex in tetralogy of Fallot patients

Patients with tetralogy of Fallot may have episodes of paroxysmal hypoxic spells ("tet spells") or could be asymptomatic. In patients who have these episodes, treatment with a beta-adrenoceptor (betaAR) blocking agent can often ameliorate or attenuate the severity of the symptoms. Additionally, excitement, crying, and situations associated with increased sympathetic activity could provoke the occurrence of these hypoxic spells. We hypothesized that altered myocardial betaAR function may contribute to the development of paroxysmal hypoxic spells in the symptomatic tetralogy patient. Surgically excised right ventricular infundibular myocardial specimens from symptomatic (patients with spells) and asymptomatic patients were used to determine total beta1 and beta2 betaAR density and betaAR adenylyl cyclase activity. Symptomatic patients had a significantly greater number of total betaAR. The relative proportion of beta1 and beta2 receptors was comparable in both patient groups. betaAR-stimulated adenylyl cyclase activity was found to be more enhanced in the symptomatic patient group. Our results indicate that infundibular betaARs may play a role in the development of paroxysmal hypoxic spells.