The role of β‐adrenergic activity in the production of cardiac and aortic arch anomalies in chick embryos

Abstract

The sympathomimetic amines isoproterenol, epinephrine, norepinephrine, and phenylephrine are structural derivatives of β‐phenylethylamine and have proportionately different effects on α‐ and β‐adrenergic receptors. Chick embryos in ovo were each administered a single dose of one of these compounds at concentrations ranging from 0.4 × 10⁻⁹ to 20 × 10⁻⁹ mol/5 μl saline during Hamburger and Hamilton stages 20–27. In other experiments embryos were pretreated with the β‐antagonist propranolol and subsequently administered isoproterenol, 743 cardiovascular anomalies were produced. The production of cardiovascular anomalies was proportional to the degree of β‐adrenergic activity of each drug. The frequency of anomalies was significantly reduced by pretreatment with propranolol. At all concentrations tested the anomaly rate was greater in chick embryos receiving an experimental compound than in controls. The general types of anomalies included aortic arch defects, ventricular septal defect, double outlet right ventricle, aortic hypoplasia, and truncus arteriosus. These results demonstrate that activation of the β‐adrenergic receptor mechanism is directly related to the cardiovascular anomalies produced in the chick embryos.