Effects of end-tidal concentrations of cyclopropane, halothane and diethyl ether on peripheral autonomic neuroeffector systems in the rat.

The effects of the inhalation anaesthetics, cyclopropane, halothane and diethyl ether were examined on peripheral neuroeffector systems in the pithed and in the conscious rat. 2 In the absence of a suitable means of accurately quantifying doses of inhalation anaesthetics given to small animals, an apparatus was constructed whereby end-tidal gas samples were collected semi-automatically from the mechanically ventilated rat. 3 Cyclopropane (15.3 and 29.3% end-tidal), halothane (0.20, 0.52 and 0.83% end-tidal) and diethyl ether (2% and 4% end-tidal) lowered the arterial pressure of the pithed rat. Heart rate was increased by diethyl ether 4%, decreased by halothane and unchanged by cyclopropane. 4 While each anaesthetic depressed the pressor responses to sympathetic nerve stimulation, cyclopropane increased and halothane and diethyl ether depressed the pressor responses to exogenous noradrenaline. 5 Each anaesthetic reduced the motor responses of the smooth muscle of the colon to parasympathetic stimulation. 6 The significance of the effects on peripheral neuroeffector systems is discussed in relation to the overall circulatory changes produced by these anaesthetics in the whole animal.