Site of alpha blockade in the demonstration of nonvagally mediated gastric acid secretion.

Results of previous reports from this laboratory have indicated that electrical centripetal vagal stimulation in the dog that has a bilateral vagotomy evokes mucus secretion from the pyloric antrum and produces an inhibition of motor activities from the stomach to the terminal ileum. We have subsequently observed that electrical central vagal stimulation after the administration of the alpha adrenolytic, phenoxybenzamine to these preparations results in general augmentation of gastrointestinal motor activity. It was also determined that electrical central vagal stimulation, using the same stimulus parameters that were stimulatory for mucus secretion, now resulted in significant increases in both volume and titratable acid secretions. The intact arterial pressor response during periods of electrical central vagal stimulation which enhanced gastric acid output in the dog that had a bilateral vagotomy eliminates the possibility that the mechanism of acid release involves the necessary suppression of the systemic pressor reflex. It is further concluded that the acid-enhancing effect of phenoxybenzamine appears to be limited to the pyloric antrum, even though the acid is secreted from the corpus. This suggests that the neural portion of the acid effect is confined to the antrum. We have successfully demonstrated that the acid-enhancing reflex effect is associated with a definite rise in the concentration of circulating gastrin.