Effect of epidural blockade on the pentazocine-induced increase in plasma catecholamines and blood pressure.

To elucidate the mechanism and site of action of pentazocine-induced sympathetic stimulation, plasma catecholamines were measured after intravenous pentazodne 1.2 mg/kg in 20 patients with epidural blockade extending to different levels. In patients with low epidural blockade (below T8) total plasma catecholamines increased during the 20-minute observation period to a ma;imnm of about 40% 5 minutes after the injection of pentazodne. The increase in catecholamines comprised mainly noradrenaline and corresponded to the rise in blood pressure and heart rate. In patients with high epidural blockade (over T6) pentazodne caused a slight fall in catecholamine level. In these patients the pentazocine-induced rise in blood pressure was nearly abolished. It is considered that the site of pentazocine-induced sympathetic stimulation is central.