Effects of injected sympathomimetic amines on plasma catecholamines and circulatory variables in man.

We measured blood pressure, heart rate (HR), and plasma catecholamine responses to a 5-minute infusion of 0.3 mg/kg d-amphetamine (d-A) and to graded bolus injections of tyramine (Tyr) to a similar increment in systolic pressure (BPs), in 9 and 7 healthy people, respectively. Both sympathomimetic agents dramatically increased BPs (mean increases peaking at 39 and 36 mm Hg for d-A and Tyr), associated with increased plasma norepinephrine (NE) (224 and 149 pg/ml) but unassociated with changes in plasma epinephrine or HR. The time course of BPs and NE responses to Tyr was much shorter than to d-A, but the pattern was similar. The results are consistent with the hypotheses that both agents increase BPs via increased synaptic cleft NE, and that circulating plasma NE reflects "spillover" from the cleft into the general circulation.