Humoral blockade on lethal pulmonary embolism in the awake dog

Humoral mechanisms have been suspected in the pathophysiology of pulmonary embolism. In this study the individual influence of α adrenergic, β adrenergic and serotonin blockade on the lethal dose of pulmonary emboli made of autologous blood clot in awake dogs was determined. The mean lethal dose of pulmonary emboli (cc clot/kg) and the standard deviation for each treatment group were as follows: untreated 1.98±0.63; methysergide treated 2.83±1.38 (P<0.05); phenoxybenzamine pretreated 2.01±0.47 (P>0.9); propranolol pretreated 2.35±0.74 (P>0.3). During embolization, all animals developed progressive tachycardia, tachypnea, dyspnea, systemic venous hypertension and systemic arterial hypotension. Systemic arterial hypotension was significantly (P<0.05) less severe in methysergide pretreated dogs than in untreated dogs. There were no significant differences between pretreated and control dogs.