Effects of ketamine on ovalbumin-induced airway hyperresponsiveness in vivo. Airway reactivity to intravenous acetylcholine (Ach) was measured 16–18 hr after the last challenge, and is given as the increase in expiratory resistance (Re). (A) Responses were calculated as log percentages of the maximum Re increase above baseline following administration of different concentrations of Ach. (B, C, D) PC100, PC200 and PC400 represent the provocation concentration required to increase Re by 100, 200 and 400%, respectively. The log transformation linear regression U-test was used to examine pair-wise differences in concentration under the same % increase of Re above baseline, with the post-hoc Bonferroni method used to adjust the P-values. The data presented are given as the mean ± SEM (n = 6–8). # P < 0.05 vs. PBS control, * P < 0.05 vs. OVA control. PBS, negative control; OVA, positive control; 12.5 mg/ml, OVA-sensitized/12.5 mg/ml nebulized ketamine-exposed/OVA-challenged; 25 mg/ml, OVA-sensitized/25 mg/ml nebulized ketamine-exposed/OVA-challenged; 50 mg/ml, OVA-sensitized/50 mg/ml nebulized ketamine-exposed/OVA-challenged; 50 μg/kg, OVA-sensitized/50 μg/kg ketamine-injected i.p./OVA-challenged; 100 μg/kg, OVA-sensitized/100 μg/kg ketamine-injected i.p./OVA-challenged.