Augmentation of Drug-induced Blood Pressure Increases in Rats by Amorbarbital

The effects of amobarbital anaesthesia on blood pressure responses to angiotensin and noradrenaline were determined in rats with chronically implanted venous and aortic catheters. Responses were tested twice on the same day in each rat, first in the conscious state and then during anaesthesia. Blood pressure rises produced by noradrenaline and angiotensin were larger when the rats were anaesthetized with amobarbital than when they were conscious. This enhancement was not characteristic of general anaesthesia since urethane, instead of enhancing, depressed the pressor responses.Blockade of acetylcholine receptors with atropine also increased the response to pressor drugs. However, amobarbital in anaesthetic doses did not affect the response to acetylcholine, indicating that removal of compensatory parasympathetic reflexes was not a major cause of its enhancing effect. The effects of amobarbital on arterial pressure and heart rate were similar to those of the ganglion blocking drug pentolinium. When pressor responses were increased by amobarbital, autonomic ganglia were depressed as indicated by the loss of the response to nicotine. These findings suggest that amobarbital enhances blood pressure responses to noradrenaline and angiotensin by blocking autonomic ganglia.