The effects of aspirin and methysergide on responses to clot-induced pulmonary embolism.

This study reports the effect of pretreatment of rabbits with aspirin and methysergide on pulmonary vascular and other responses to clots introduced into the lobar pulmonary artery. Pretreatment with 250 mg/kg aspirin significantly (p less than 0.01) reduced the pulmonary artery pressure, the heart rate, and the systemic blood pressure changes induced by embolization. Pretreatment with methysergide 3 mg/kg also significantly (p less than 0.005) reduced the pulmonary artery pressure rise but had no effect on heart rate, systemic blood pressure, or ventilation rate. Pretreatment with a combination of aspirin and methysergide produced an additive effect and reduced the pulmonary artery pressure rise at 2 minutes post embolization from 10 +/- 2 mm Hg in control subjects to 1.3 +/- 0.9 mm Hg. There were no significant alterations in heart rate, systemic blood pressure, or ventilation rate following combined treatment. Responses to arachidonic acid and serotonin were virtually abolished by aspirin and methysergide, respectively. These results suggest a positive role for more than one mediator in the response to clot-induced pulmonary embolism.