Platelet-activating factor increases lung vascular permeability to protein.

Area of Science:

• Pulmonary circulation
• Vascular physiology
• Inflammation research

Background:

• Platelet-activating factor (PAF) is a potent mediator implicated in various physiological and pathological processes.
• Cyclooxygenase (COX) metabolites are known to influence pulmonary hemodynamics and vascular permeability.
• Understanding the specific roles of PAF and COX pathways in the lung is crucial for managing respiratory conditions.

Purpose of the Study:

• To investigate the effects of PAF on pulmonary hemodynamics and microvascular permeability in unanesthetized sheep.
• To determine the involvement of the cyclooxygenase pathway in PAF-induced pulmonary responses.
• To assess the direct impact of PAF on endothelial cell permeability in vitro.

Main Methods:

• Infusion of PAF in unanesthetized sheep with lung-lymph fistulas to measure pulmonary arterial pressure, vascular resistance, thromboxane B2, and lymph flow.
• Administration of sodium meclofenamate (a COX inhibitor) prior to PAF infusion to assess pathway involvement.
• In vitro studies using cultured bovine pulmonary artery endothelial cells to measure albumin permeability upon PAF exposure.

Main Results:

• PAF infusion increased pulmonary arterial pressure, vascular resistance, thromboxane B2 levels, and pulmonary lymph flow.
• Sodium meclofenamate pretreatment blocked PAF-induced thromboxane B2 generation and hemodynamic changes but not the increase in lymph flow.
• PAF did not directly alter endothelial cell albumin permeability in vitro, suggesting indirect mechanisms for increased vascular permeability in vivo.

Conclusions:

• PAF induces pulmonary vasoconstriction mediated by cyclooxygenase metabolites.
• PAF increases pulmonary vascular permeability to proteins through a mechanism independent of cyclooxygenase products.
• The observed increase in vascular permeability is not a direct lytic effect of PAF on endothelial cells.