Toxic effects of hypoxia on neonatal cardiac function in the rat: alpha-adrenergic mechanisms

Stimulation of peripheral alpha-adrenergic receptors by circulating catecholamines derived from the adrenal medulla is essential for surviving neonatal hypoxia. In 1-day-old rats, where sympathetic innervation of cardiovascular sites has not yet developed, blockade of these receptors results in failure of cardiac performance from a progressive decline in sinus rate and atrioventricular conduction deficits. These effects are absent in 8-day-old rats, where sympathetic efferent innervation has become established.