Release of immunoreactive serotonin following acid perfusion of the duodenum.

Cannulas were placed in the portal vein, hepatic vein, and infrarenal vena cava in eight anesthetized dogs. The duodenum of each dog was irrigated with saline (control) and 0.1 N HCI (50 ml in 10 min). Heparinized blood samples were taken from each cannula 5 min before, and 1, 5, 10, 30 and 60 min after each irrigation for measurement of immunoreactive serotonin concentrations. Serotonin concentrations did not change during saline irrigation of the duodenum. In contrast, serotonin release was consistently observed after duodenal acidification (pH 1.5-2.0). Portal venous serotonin concentrations were increased at 1 min (356 +/- 147 ng/ml) and following a biphasic pattern remained elevated at 30 and 60 min (499 +/- 131 and 489 +/- 187 ng/ml, respectively). Concentrations in the hepatic vein rose more slowly and to a lower peak (357 +/- 123 ng/ml at 10 min). Caval serotonin concentrations were increased at 10 min (342 +/- 121 ng/ml) but promptly returned to baseline levels. In the canine gastrointestinal tract, immunoreactive serotonin concentrations were highest in the duodenal bulb (15.4 mug/gm). This study demonstrated serotonin release from the duodenum following acid perfusion and documented that some of the released serotonin escaped hepatic inactivation. These findings support the possibility that serotonin may be a gastrointestinal hormone involved in the feedback inhibition of gastric acid secretion.