Sympathomimetic effects of amezinium on the cardiovascular system and plasma catecholamines in man

The cardiovascular effects of the sympathomimetic agent amezinium were investigated in a double-blind, placebo-controlled, randomized trial in six volunteers. Before and 2 h after oral administration of amezinium 30 mg or placebo the cardiovascular responses to orthostatic stress, induced by 80 degrees passive head-up tilt, were assessed by recording blood pressure, systolic time intervals, and echocardiogram. Plasma catecholamines were also determined. After amezinium treatment, the average supine systolic blood pressure was increased by +30 mm Hg and after tilting it remained above both the pre-treatment and placebo values. Compared to placebo, amezinium elicited only minor changes in heart rate and diastolic blood pressure. The effect of amezinium on the pre-ejection period corrected for heart rate (PEPc) and mean velocity of fiber shortening (VCFmean) indicated positive inotropic properties. Its effects were distinctly more pronounced during tilt than with the subjects supine. Plasma concentrations of noradrenaline and adrenaline were not influenced by amezinium during rest or tilt. From these results and previous research it is concluded that amezinium induces its sympathomimetic effects by preferentially inhibiting the re-uptake of noradrenaline which is released by the drug itself, or by sympathetic activation during tilt. This mechanism of action might explain the pronounced sympathomimetic effects of the drug, especially during orthostatic stress.