Are young platelets released in excess from the spleen in response to short-term physical exercise?

With a view to throwing some light on the age characteristics of platelets released into the blood in response to short-term physical exercise, we conducted exercise experiments on 23 healthy subjects previously injected with different platelet populations labelled with 111In and 51Cr. Based on comparative platelet kinetic studies of pre- and post-exercise platelets and on exercise experiments carried out while labelled-platelet populations of different age composition were circulating, we cannot support the concept that the platelets released into the blood in response to exercise are enriched with young platelets. In addition, we found that simultaneously-injected large and small platelets were released to the same extent in response to exercise, but that the sequestration patterns of large and small platelets seem to be different.