Hemodynamic Responses of Broiler Pulmonary Vasculature to Intravenously Infused Serotonin

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Serotonin is a potent pulmonary vasoconstrictor actively accumulated by mammalian platelets and avian thrombocytes and released into the plasma during platelet or thrombocyte aggregation. Serotonin has been implicated in the mechanisms responsible for pulmonary hypertension in several human and animal studies. However, the role of serotonin in pulmonary hypertension syndrome (PHS, ascites) in broilers previously had not been evaluated. In the present study we evaluated the pulmonary hemodynamic responses of broilers to intravenous infusions of serotonin dissolved in 2.5% (wt/vol) mannitol solution (carrier vehicle). Carrier vehicle infusion alone had no influence on any of the hemodynamic variables. Serotonin infusion triggered rapid increases in pulmonary arterial pressure to approximately 50% above pre-infusion baseline values, accompanied by decreases in mean systemic arterial pressure and cardiac output. The peak pulmonary arterial pressure response occurred within approximately 70 s after the start of serotonin infusion and remained elevated above baseline values over the course of a 10-min infusion period. Pulmonary arterial pressure and cardiac output returned to pre-infusion baseline values upon cessation of serotonin infusion, whereas mean systemic arterial pressure returned toward pre-infusion base-line values. Pulmonary hypertensive responses were associated with increased pulmonary vascular resistance (pulmonary vasoconstriction). The peak pulmonary arterial pressure attainable was inadequate to propel the normal cardiac output through the elevated pulmonary vascular resistance. Consequently, the impeded venous return to the left ventricle caused dependent reductions in stroke volume, cardiac output, and mean systemic arterial pressure. Reductions in cardiac output were associated with reductions in stroke volume but not heart rate. Any factor that reduces the pulmonary vascular capacity or increases the pulmonary vascular resistance theoretically can increase the incidence of PHS. The present study provides direct evidence that serotonin can trigger pulmonary vasoconstriction and pulmonary hypertension in broilers.