Relation of age to effects of phentolamine and phenylephrine on heart

In the present study, the responses of neonatal and adult dog hearts to phenylephrine (PE) and phentolamine (PA) were investigated in order to determine the influence of age factors. PA resulted in the slowing of the heart rate, the prolongation of corrected sinus node recovery time, atrial refractory period (ARP), ventricular effective refractory period (VERP), and ventricular functional refractory period (VFRP), and a significant inhibition of conducting tissues in neonatal dogs. In contrast, no such effects were seen in adult dogs. PE had a positive chronotropic effect in neonatal dogs but no such effect in adult dogs. In conclusion, alpha-adrenoceptors played an important excitatory role in the neonatal dog heart.