[Effect of clonidine on plasma-catecholamine levels at rest and on ergometric exercise (author's transl)]

The effect of clonidine on peripheral venous-plasma catecholamine concentration was assessed in ten subjects with normal circulation, at rest and on submaximal bicycle exercise. Three hours after oral intake of 300 micrograms clonidine in single dose there was significant lowering of the plasma adrenaline and noradrenaline levels. Six hours after intake the lowest plasma catecholamine level was reached, but after 24 hours the clonidine effect had largely disappeared. The sympatholytic effect of clonidine was relatively less marked with bicycle exercise than at rest. When clonidine had been given for only a short period at moderate dosage, there was no exaggerated catecholamine rise. Clonidine administration did not effect plasma dopamine levels. These results indicate that clonidine decreases plasma adrenaline and noradrenaline levels without significant effect on circulatory regulation.