The effects of low-dose epinephrine infusion on spleen size, central and hepatic circulation and circulating platelets

In several conditions associated with adrenergic stimulation, an increase in peripheral count of larger platelets has been observed, but the mechanism remained elusive. Larger platelets have greater prothrombotic potential and increase the risk of acute thrombotic events. The human spleen retains one-third of total body platelets, with mean volume (MPV) about 20% greater than that of circulating platelets. We aimed to answer whether low-dose epinephrine infusion results in spleen contraction and MPV increase. We undertook the continuous ultrasonic measurements of spleen volume, hepatic and central circulation with concurrent blood sampling in response to intravenous infusion of epinephrine (6 min of 0.06 mu g kg-1 per min, followed by 3 min of 0.12 mu g kg-1 per min) in nine healthy young subjects. The spleen volume started to decrease immediately after the onset of infusion, in the presence of substantial decreases in peripheral resistance and mean blood pressure and increases in heart rate and cardiac output. The majority of spleen emptying, approximately 25%, (95% CI 71.3299.7) was observed 1 min after infusion onset, the hepatic vein flow peaked at the end of infusion for 28.4% (95% CI 1074.6407.9), while increases in platelet count for approximately 31% (95% CI 187.8314.8) and MPV for 4.4% (95% CI 7.310.9) lagged until 1 min after infusion cessation. We suggest that spleen is a dynamic reservoir of large platelets, which are mobilized even by low-dose epinephrine infusion in conditions of decreased blood pressure.