Vasoactive Substances in Pulmonary Embolism

Embolisation of the pulmonary vasculature with microspheres releases prostaglandin-1ike substances, PGLS (Piper and Vane, N.Y. Acad. Sei. 180: 363, 1971) but the capacity of autologous blood clots (ABC) to release pulmonary vasoactive substances is disputed. Ten normal mongrel dogs were anesthetised with pentobarbitone sodium and instrumented. Pulmonary venous blood was continuously superfused over isolated tissues for bioassay and then returned to the animal. Injection of ABC into the right atrium increased pulmonary artery pressure from 21 ± 6.5 mm Hg to 38 ± 15 mm Hg (mean ± S.D.), increased arterial pCO2 and decreased arterial pO2. No significant changes in heart rate, systemic arterial blood pressure or cardiac output occurred. In three animals contractions of the blood superfused assay tissues occurred following embolism. This effect was produced in normal assay tissues and those pretreated with antagonists of ACh, Serotonin, Histamine and Catecholamines and could therefore be attributed to PGLS. No cardiovascular or assay tissue tension changes were observed when equivalent volumes of saline or clot lysate were injected into the right atrium.Therefore, pulmonary embolism with ABC can release PGLS which may contribute to the pulmonary artery pressure rise. Vasoactive substances may normally be inactivated in the lung but in some animals appear in pulmonary venous blood. (Supported by the Ontario Heart Foundation)