Fig. 3. Guinea pig tracheal ring muscle force generated in response to exogenous acetylcholine-induced contraction expressed as percent change from baseline peak contraction and response to the addition of intravenous anesthetics to the organ bath. (A) Propofol, 0.5–100 μm (n = 10); (B ) thiopental, 0.5–200 μm (n = 11); (C ) ketamine, 0.5–50 μm (n = 5); (D ) etomidate, 0.008–16 μm (n = 5). *P < 0.05, ***P < 0.001. Data are presented as mean ± SEM. Only thiopental relaxed exogenous acetylcholine-induced contraction at concentrations routinely reached clinically.