Evidence of α-Adrenoceptor-Mediated Chronotropic Action in Children

We investigated α-adrenoceptor-mediated positive chronotropic action in children using a pharmacological autonomic function test. Under cardiac vagal and sympathetic blockade, chronotropic responses to intravenous infusion of an α-agonist, phenylephrine, were determined in 129 patients with suspected autonomic dysfunction. Heart rate changes to phenylephrine infusion (0.4 μg/kg/min) for 5 minutes ranged from −2 to 50 beats/min (mean ± SD, 13.8 ± 9.7 beats/min). α-Adrenoceptor-mediated chronotropic (APC) action more than 5 beats/min was observed in 88 (68%) subjects. APC was negatively correlated with age. Multivariate analysis showed that APC was correlated negatively with β-sympathetic tone and positively correlated with intrinsic heart rate. These results suggest that the α-adrenoceptor-mediated chronotropic action is a developmental phenomenon and may play an important role in controlling heart rate in response to cardiac sympathetic activation.