Effect of cervical and thoracic vagal stimulation on luminal serotonin release and regional blood flow in cats

In acute experiments on 14 cats, the transected vagus nerves were stimulated at two levels (10 V, 5 ms, 10 Hz, 10 mA, 15 min). Fifteen-centimeter proximal jejunal segments were perfused with saline (1.0 ml/min). Basal luminal immunoreactive serotonin secretion averaged 206 ± 67 ng/5 min. After stimulation of the vagus nerves, there was an immediate two- to threefold increase in the rate of secretion of immunoreactive serotonin into the lumen. There were no significant differences in the stimulated secretory rates that resulted from stimulation at the cervical or thoracic levels. Shortly after cessation of vagal stimulation, immunoreactive serotonin secretory rates returned to basal. Vagal nerve stimulation did not result in any change in peripheral or portal venous blood concentrations of serotonin. In 12 additional cats, the effects of stimulation of the vagus nerves at the cervical and thoracic levels on regional blood flow, as determined using the microsphere technique, were compared. Cervical vagal stimulation resulted in hypotension, bradycardia, decreased perfusion of the heart, kidney, and small and large bowels, but preservation of the perfusion of the fundus and antrum. In contrast, stimulation of the transected nerves in the chest stimulated gastric blood flow but did not alter either flow to other viscera or central hemodynamics.