Platelet-activating factor effects on pulmonary ultrastructure in rabbits.

Morphometric analysis of endothelium in rabbit lungs demonstrated a dramatic effect of platelet-activating factor (PAF) on the ultrastructure of pulmonary vasculature. Plasmalemmal vesicles in capillaries were increased both in size (638 A PAF vs 538 A control) and in number (386/micrograms 3 cytoplasm PAF vs 125/micrograms 3 cytoplasm control) when PAF was administered as a single acute low dose (chi less than 3 micrograms/kg). High concentrations of PAF (chi greater than 3 micrograms/kg) as a single acute dose also increased vesicle number (203/micrograms 3 cytoplasm), but frequently precipitated the respiratory distress syndrome. Chronic administration of PAF with daily doses over periods of either 3.5 or 7 weeks resulted in changes paralleling the acute observations, but did not lead to more extensive lung disease.