Four studies were designed to test the hypothesis that platelet catecholamine levels may provide a stable index of circulating plasma catecholamine concentrations, and that these are unaffected by acute elevations of plasma levels with physical and psychological stress. 2. To assess the biological variability within individuals, ten subjects were sampled on five occasions over 8-30 h. The intra-individual coefficients of variation for plasma and platelet noradrenaline levels were 19.5 +/- 10% and 9.5 +/- 4.2%, respectively, and for plasma and platelet adrenaline levels 48.3 +/- 22% and 25.3 +/- 8.4%, respectively. 3. Three other studies investigating the response to physical and psychological stress were performed. In the first study, plasma and platelet catecholamine levels were studied in 12 healthy subjects before and after bicycle ergometry. Plasma catecholamine concentrations increased [noradrenaline by +346 +/- 323% (P = 0.002) and adrenaline by +314 +/- 352% (P = 0.003)], whereas platelet concentrations showed little change [noradrenaline +4 +/- 18% (P = 0.94) and adrenaline +38 +/- 116% (P = 0.67)]. 4. In the study, catecholamine concentrations were measured in eight subjects after hand immersion in iced water. Plasma noradrenaline concentrations increased significantly (+58 +/- 19%, P = 0.001), but no significant change was found in plasma adrenaline concentrations (+8 +/- 44%, P = 0.48). Platelet catecholamine concentrations showed no significant change (noradrenaline +15 +/- 15%, P = 0.052, and adrenaline 19 +/- 82%, P = 0.84). 5. In the third study, catecholamine concentrations were measured in 22 medical students before and after their end-of-year examination.(ABSTRACT TRUNCATED AT 250 WORDS)
