Abstract
Although the location and mechanism of increased lung vascular permeability in pulmonary microembolism are still controversial, it has been suggested that vascular permeability could increase in open perfused portions of the microvascular bed by physical injuries. To test this hypothesis, unilateral microembolization was induced in anesthetized dogs by injected glass beads (80-120μm in diam., 0.1g/kg) into the right pulmonary artery and the filtration coefficient of the nonebolized left lower lobe was measured according to weight transient method of Drake and his associates. The filtration coefficient of the left lower lobe was doubled 30 minutes after microembolization, and the calculated vasculated resistance of left lower lobe did not change significantly. To further investigate the contribution of microvascular endothelial cell injury to a sequence leading to the heightened pulmonary vascular permeability, the concentration of 6-keto PGF1α in the arterial blood was measured by radioimmunoassay and found to increase progerssively following microembolization. Pretreatment by indomethacin (10mg/kg) resulted in an increase in the filtration coefficient not only 30min but also 60min after embolization. The calculated arterial resistance increased significantly immediately after microembolization. Coutinuous infusion of PGI2 methyl ester (20ng/kg/min) prevented an increase in the filtration coefficient observed at 30min following microembolization. By administration of mepyramine maleate, histamine H1-blocker, (3.0mg/kg bolus+1.5mg/kg/hour) neither the filtration coefficient nor the concentration of 6-keto PGF1α increased following microembolization.
Based on these results, the author concluded that:
(1) The lung vascular permeability increased in the nonembolized portion after microembolization. (2) Endogenous PGI2 could be responsible for protection against increased lung vascular permeability induced by microembolization. (3) The release of endogenous PGI2 could be mediated by histamine through H1-receptor action. (4) Although glass beads activate Hageman factor resulting in activation of kinin system, histamine could play an important role in increased lung vascular permeability following microembolization in the present experiment.
