Exercise-induced changes in the in vivo distribution of 111In-labelled platelets.

In order to throw some light on the mechanisms underlying exercise-induced thrombocytosis, we investigated 15 healthy persons subjected to short-term vigorous pedalling on a bicycle ergometer 1 d after injection of autologous 111In-labelled platelets. Scintigraphic studies during the post-exercise period showed the spleen to be the major platelet-releasing organ. There was, however, a considerable interindividual variability manifested as signs of a contributing platelet release from the lungs in some cases and of deposition of a surplus of released platelets in the liver of others. Our results also seem to be compatible with the existence of an intravascular marginal platelet pool.