Platelet activating factor (PAF) is a potent stimulator of porcine tracheal fluid secretion in vitro.

Mucus hypersecretion is a major clinical feature of chronic obstructive lung diseases such as asthma. The possible role of the inflammatory and bronchoconstrictor ether lipid PAF (platelet activating factor) has been studied in isolated porcine trachea with the tantalum 'hillock' technique used to visualize fluid production from tracheal submucosal glands. PAF caused a rapid, dose-dependent (0.001-1 nM) stimulation of fluid secretion which could be detected after 5 min and which increased with time up to at least 15 min. The PAF-induced fluid secretion was unaffected by both antagonists of histamine, acetylcholine and leukotriene D4 and inhibitors of prostaglandin and leukotrienes synthesis. A purported PAF receptor antagonist (CV 3988) inhibited the PAF responses in a dose-dependent manner implying a receptor-mediated event. These results may be of relevance to the mucus hypersecretion seen in chronic airway diseases.