Inhibition of depressor cardiovascular reflexes by a derivative of gamma-aminobutyric acid (GABA) and by general anesthetics with suspected GABA-mimetic effects.

Several general anesthetics and baclofen (Lioresal), an analog of gamma-aminobutyric acid, were tested for their effects on reflexes evoked by stimulation of afferent fibers in the carotid sinus nerve, aortic nerve and cervical vagus nerve. In both anesthetized and decerebrate unanesthetized cats, baclofen, barbiturates (methohexital and pentobarbital) and alpha-chloralose converted depressor responses evoked by afferent fiber stimulation to pressor episodes. The original depressor responses were reinstated temporarily by the gamma-aminobutyric acid antagonists bicuculline and picrotoxin, but not by strychnine or pentylenetetrazol. Baclofen, chloralose and barbiturate general anesthetics also blocked the inhibition of aortic nerve, carotid sinus nerve and vagus nerve stimulation of neural sympathetic vasomotor discharges. Other general anesthetics (halothane, nitrous oxide, urethane and ketamine) did not have these effects. The effects of baclofen, barbiturates and chloralose are attributed to selective blockade of baroreceptor reflexes. It is suggested that the underlying mechanism may be related to enhancement or imitation of the action of gamma-aminobutyric acid at central vasomotor synapses.