Developmental Changes of the Alpha1-Adrenergic System in the Rat Heart

The effect of alpha$_1$-adrenergic stimulation on cardiac automaticity changes during myocardial development. To illustrate, in isolated tissues from the mature canine heart, alpha$_1$-adrenergic stimulation usually induces a decrease in automatic rate. On the other hand, many early neonatal fibers exhibit an increase in automatic rate In response to alpha$_1$-agonists, which is not seen in the adult.