Lung responses and platelet release reaction following induced intravascular platelet aggregation in the cat

Pulmonary microembolism secondary to intravascular platelet aggregation causes a rise in pulmonary vascular resistance and a decrease in dynamic lung compliance. The relationship between these lung responses and the platelet release reaction was investigated in the cat. Repeated episodes of platelet aggregation were induced by intravenous infusions of either ADP or collagen. Platelet release was evaluated by serial determinations of the plasma concentration of platelet factor 4 (PF-4). An increased plasma concentration of PF-4 was found after the initial episode of such induced intravascular platelet aggregation. Consecutive infusions of an aggregating agent still elicited vigorous lung responses, but no further increase in the plasma concentration of PF-4 was observed. There are different possible explanations for this lack of correlation between the lung responses and the PF-4 release. It may well be that the pattern of release for PF-4 does not reflect those release events which result in pulmonary smooth muscle contraction. Alternatively, but less likely, pulmonary smooth muscle constriction and platelet release could be fully independent phenomena.