Platelet catecholamine contents as related to trait anxiety and aerobic fitness.

Abstract

Platelet catecholamines (CA) are derived from plasma and are considered as a cumulative index of sympathoadrenal activity. We investigated whether trait anxiety (TA) and aerobic fitness, two interrelated long-term determinants of sympathoadrenal activity, affect platelet CA concentration as measured in rest and after acute increments of plasma epinephrine (Epi). For that purpose, platelet CA were measured 15 min before and after Epi infusion (5-160 ng.kg-1.min-1, increased in 6 steps) in 45 healthy male students with high (n = 21) and low (n = 24) TA, of whom maximal aerobic power (VO2max) was assessed. Plasma CA and electrolytes were measured during each infusion rate. Epi infusion significantly raised platelet Epi by 67% and decreased platelet and plasma norepinephrine (NE) by 23 and 17%. Plasma potassium significantly decreased by 32% and plasma sodium slightly increased. Platelet Epi increase was inversely related to basal platelet Epi (r = -0.58, P less than 0.001). Platelet NE decrease was positively associated with basal platelet NE and plasma potassium levels (r = 0.50, P less than 0.01). TA and VO2max were not related to basal levels and responses of electrolytes and platelet NE. VO2max was correlated with platelet Epi increase in low TA (r = 0.62, P = 0.002), whereas no such relationship existed in high TA (r = 0.008). We conclude that fitness positively influences platelet Epi accumulation, but that high TA interferes with this relationship.