Fig. 2. Guinea pig tracheal ring muscle force generated in response to nonadrenergic, noncholinergic (NANC) electrical field-stimulated (EFS) contraction expressed as percent change from baseline contraction and response to the addition of intravenous anesthetics to the organ bath. (A ) Propofol, 5–100 μm (n = 9); (B ) thiopental 5–200 μm (n = 8); (C ) ketamine, 0.5–50 μm (n = 11); (D ) etomidate, 0.008–16 μm (n = 10). *P < 0.05, **P < 0.01, ***P < 0.001. Data are presented as mean ± SEM. Only propofol relaxed NANC EFS-induced contraction at clinically relevant concentrations.