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SummaryThe spleen is well-known as a site for platelet pooling, although the mechanisms controlling intrasplenic platelet transit are essentially unknown. We tested the possibility that thromboxane A2 might be involved in this control by measuring intrasplenic platelet transit time in 10 subjects receiving a specific thromboxane A2 receptor antagonist (AH23848B; 70 mg; Glaxo Group Research Ltd), in 10 receiving aspirin (300 mg) plus dipyridamole (75 mg), and in 9 receiving placebo. All doses were administered 3 times daily commencing 4 days prior to transit time measurement.Mean intrasplenic platelet transit time was measured by monitoring the kinetics of equilibration of 111In radiolabelled platelets between blood and spleen following intravenous injection. There was no difference between the mean transit time in the 3 groups of subjects, lending no support to the hypothesis that thromboxane A2 is involved in the control of platelet traffic through the spleen.

Thrombus formation within arterial aneurysms may lead to embolisation and distal ischaemia. We have investigated the use of 111-indium labelled platelets in the diagnosis of atherosclerotic and false aneurysms. Autologous platelets labelled with 111-indium oxine were injected into patients with eleven proven aneurysms (8 atherosclerotic, 3 false) . Gamma camera imaging performed between 24 and 72 hours later was positive for 10 of the aneurysms. In every case there was increased uptake of label over the aneurysm when compared to undiseased blood vessels (p < 0.05). Most aneurysms could be demonstrated within 24 hours of labelling platelets. 111-indium labelled platelets may prove useful in identifying the source of peripheral arterial emboli.

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