Platelets and bronchospasm.

The intrathoracic accumulation of radiolabelled platelets and concomitant changes in airway resistance have been recorded continuously in anaesthetised guinea pigs. Platelet-activating factor (PAF-acether) and antigen (in sensitised animals) elicited dose-related intrathoracic accumulation of platelets that could be associated with an increase in airway resistance. Maximal increases in airway resistance preceded maximal increases in platelet accumulation. Low doses of antigen could elicit substantial platelet accumulation, without detectable changes in lung function. It is concluded that physical obstruction of the pulmonary vasculature is not the sole determinant of platelet-dependent bronchoconstriction.