Role of 5-HT2 receptor inhibition in pulmonary embolization

We examined the role of serotonin at the 5-HT2 receptor site after pulmonary embolization for changes in hemodynamics, gas exchange, and lung water. Pulmonary embolization was induced using 0.75 gm/kg autologous clot in anesthetized artificially ventilated dogs. Pulmonary vascular resistance rose by 5 min from 3.4 +/- 1.5 to 14.2 +/- 2.1 mm Hg/liter/min (p less than 0.001), arterial oxygenation decreased from 91 +/- 5 to 68 +/- 5 mm Hg (p less than 0.01), platelet count decreased from 201 +/- 64 to 141 +/- 32 ml X 10(3), and the wet to dry weight lung ratio increased from 2.59 +/- 0.34 to 4.21 +/- 0.21 (p less than 0.001). Inhibition by ketanserin, a selective serotonergic inhibitor at the 5-HT2 receptor site substantially attenuated the increase in pulmonary vascular resistance from 3.6 +/- 1.4 to 8.0 +/- 2.5 mm Hg/liter/min, ablated the hypoxemia and platelet reduction and inhibited the formation of pulmonary edema. Infusion of serotonin simulated only some of the above changes as the pulmonary vascular resistance increased from 3.16 +/- 1.6 to 13.5 +/- 4.1 mm Hg/liter/min (P less than 0.01) and the oxygenation decreased from 96 +/- 5 to 57 +/- 4 mm Hg (P less than 0.01). Serotonin infusion, however, did not cause pulmonary edema. The administration of ketanserin ablated the increase in pulmonary vascular resistance and the hypoxemia following serotonin infusion. We conclude that following pulmonary embolization, serotonin at the 5-HT2 receptor is responsible for the fall in PaO2 and partially responsible for the increased pulmonary vascular resistance. Although ketanserin inhibits the formation of pulmonary edema following pulmonary embolization, serotonin does not seem to be directly responsible.