The functional significance of anatomically reduced cardiac sympathetic innervation in the newborn is not known. This problem was investigated by examining ventricular contractile responses to repeated maximal left stellate ganglion stimulation in adrenalectomized and sham-adrenalectomized newborn (4-12 days of age) and adult dogs. At the end of five periods (5 min/period) of stimulation, sham-adrenalectomized puppies were still able to augment left ventricular force 13.0 +/- 3.8% (mean +/- SE; P less than 0.05) above control values. However, adrenalectomized puppies did not maintain their ability to enhance left ventricular force after the first period of stimulation. Similar results were obtained with measurements of the first 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 five stimulation periods whether or not their adrenal glands were intact. After five stimulation periods, adrenalectomized newborn dogs responded to isoproterenol, indicating that their cardiac beta-adrenergic receptors remained functional. We conclude that 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 that adrenal integrity is required in the newborn to maintain appropriate ventricular responses to sympathetic stimulation.