Mechanism whereby halothane reverses the pressor responses to acetylcholine.

The initial and secondary components of the biphasic pressor response to acetylcholine in the atropinized dog were analysed separately. Deep halothane anaesthesia reversed the initial pressor response to acetylcholine owing to a decrease in total peripheral vascular resistance in the absence of an increase in cardiac output. The secondary pressor response was not reversed but was suppressed owing to a marked reduction of the increase in cardiac output responsible for this pressor response; total peripheral resistance increased.