Adrenaline was infused in incremental doses of 0.05 up to 0.1 microgram/kg/min over a 60-min period in nine patients with mild essential hypertension and six age-matched normotensive controls. Blood samples were drawn at preset time intervals and plasma adrenaline, platelet count, serum thromboxane B2 (TxB2) and plasma beta-thromboglobulin (beta-TG) were measured. Adrenaline levels (m +/- SEM) rose significantly, from 0.078 +/- 0.01 (baseline) to 0.902 +/- 0.03 ng/ml (60 min), in the hypertensive group; a similar increase was observed in the control group (from 0.049 +/- 0.007 to 0.877 +/- 0.03 ng/ml). Platelet count increased significantly at early time points and remained high throughout infusion in both groups (hypertensive from 250 +/- 25 to 305 +/- 24 x 10(3)/microliters, control from 219 +/- 16 to 260 +/- 18 x 10(3)/microliters). TxB2 levels likewise increased significantly from 15 minutes after initiation of infusion. In hypertensive subjects the mean resting value of 186 +/- 17 ng/ml rose to 312 +/- 42 ng/ml, while in control subjects the resting value of 174 +/- 29 ng/ml rose to 286 +/- 32 ng/ml. Baseline levels of TxB2 were found to be higher in the hypertensive patients but not significantly. beta-TG levels increased from an initial value of 43.84 +/- 3.69 ng/ml to 59.5 +/- 4.69 ng/ml at 60 min in the hypertensive group, while a similar change from 28.7 +/- 19.2 ng/ml to 40.36 +/- 3.16 ng/ml was observed in the control group. These changes were significant, as was the difference between basal values in the two groups.(ABSTRACT TRUNCATED AT 250 WORDS)