Platelet catecholamine contents are cumulative indexes of sympathoadrenal activity.

Blood platelets continually accumulate catecholamines (CA) from plasma. Plasma CA levels fluctuate rapidly, but platelet CA appear to have a slower turnover, making them potentially useful as long-term indexes of sympathoadrenal activity. We measured the effect of different types of human physical exertion on epinephrine (E), norepinephrine (NE), and dopamine (DA) and their sulfoconjugates in both plasma and washed platelets using a radioenzymatic assay. Acute strenuous exercise caused only a small (26%) rise in unconjugated plus sulfated platelet E, but regular training (140 +/- 30 km/wk) was associated with levels of platelet CA or CA sulfates 39-112% higher than controls. After completion of an ultramarathon (607-1,020 km in 6-8 days), platelet CA and CA sulfates were 139-405% higher than controls. Platelet CA declined over several days postrace, and the loss of platelet NE was significantly slower than the loss of platelet E. Plasma CA sulfates were significantly elevated in the runners, whereas plasma CA were normal apart from a transient elevation in NE postrace. Platelet CA levels provide a useful index of chronic sympathoadrenal activity but may be affected by changes in platelet turnover or activation.