The effects of exogenously infused serotonin on central and regional hemodynamics were investigated in 14 dogs. Using intravenous doses that mimic postprandial levels of serotonin, we were able to demonstrate no changes in cardiac output or mean arterial pressure. However, there were region-specific changes in blood flow. Blood flow to the fundus, antrum, brain, heart, and skeletal muscle were increased by both the low-dose (4 μ/kg-min) and the high-dose (10 μg/kg-min) infusions. In contrast, blood flow to the kidney, spleen, and liver decreased. Whole blood 5-HT levels were measured in mixed venous blood and systemic arterial blood. Based on the differences between serotonin levels in these two circulations, pulmonary inactivation of exogenously infused serotonin was calculated to be 44%. The half-life of exogenous serotonin was measured at 1.2 min. The data thus suggest that at doses which mimic those released from the intestinal enterochromaffin cells, serotonin may play a role in mediating postprandial hemodynamic responses.
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