Effects of ketamine and halothane on normal and asthmatic smooth muscle of the airway in guinea pigs.

In vitro preparations of trachea isolated from normal and asthmatic guinea pigs were used to measure their maximum contractile response to histamine challenge and to determine spontaneous relaxation of smooth muscle of the airway. The effect of ketamine and halothane on these reactions was investigated. The optimal ketamine concentration was found to be 10 micrograms/ml. This dose attenuated the maximum contraction and produced greater relaxation (p less than 0.01) of isolated trachea. However, ketamine failed to prevent an anaphylactic (Schultz-Dale) response when antigen (one per cent albumin) was added in an experimental chamber containing pre-sensitized guinea pig trachea. In contrast, halothane abolished any response to histamine challenge and prevented development of the Schultz-Dale response of smooth muscle from the airway of asthmatic guinea pigs.