The exchangeable splenic platelet pool in response to intravenous infusion of isoprenaline

8 healthy volunteers and 4 asplenic subjects, in whom autologous platelets had been labelled with radioactive sodium chromate, received i.v. infusions of isoprenaline in a dose of 0.03 microgram x kg-1 x min-1 over a period of 6 min. In the former group these infusions caused a significant decrease in the concentration of labelled as well as unlabelled platelets in the peripheral blood. Body surface countings showed that a significant increase in the count rate over the spleen occurred concomitantly with the decrease in the circulating platelet-bound radioactivity (PBR). In the group of asplenic subjects no change in PBR occurred. It is concluded that adrenergic beta-receptor stimulation causes a transitory trapping of platelets in the exchangeable splenic platelet pool.