Functional significance of reduced cardiac sympathetic innervation in the newborn dog

Abstract

The functional significance of anatomically reduced cardiac sympathetic innervation in the newborn is not known. Ventricular contractile responses to repeated maximal left stellate ganglion stimulation were examined in adrenalectomized and sham-adrenalectomized newborn (4-12 days of age) and adult dogs. At the end of 5 periods (5 min/period) of stimulation, sham-adrenalectomized puppies were still able to augment left ventricular force 13.0 .+-. 3.8% (mean .+-. SE; P < 0.05) above control values. Adrenalectomized puppies did not maintain their ability to enhance left ventricular force after the 1st period of stimulation. Similar results were obtained with measurements of the 1st time derivative of left ventricular force (dF/dt), right ventricular force, right ventricular dF/dt and peak left ventricular pressure. Adult dogs were able to augment these measurements of cardiac function significantly throughout 5 stimulation periods whether or not their adrneal glands were intact. After 5 stimulation periods, adrenalectomized newborn dogs repsonded to isoproterenol, indicating that their cardiac .beta.-adrenergic receptors remained functional. Evidently, the known sparse ventricular sympathetic innervation in the newborn dog is associated with inability to maintain significant cardiac functional responses after repeated sympathetic stimulation and adrenal integrity is required in the newborn to maintain appropriate ventricular responses to sympathetic stimulation.