Fig. 2. Dose- and time-dependent sedative effects of paired intraperitoneal combinations of arachidonyl-2-chloroethylamide (ACEA) and etomidate in the Rota-Rod test (Rota-Rod; Ugo Basile, Comerio, Italy) in mice ( A ). The combinations were of equal fractions (0.1, 0.25, 0.33, 0.4, 0.5, 0.6, and 1.0) of each paired drug’s respective ED50value coadministered in a fixed 1:1 ratio of the ED50of ACEA:ED50of etomidate. Time on the Rota-Rod (in seconds) is shown from 0 min (bolus injection) to 90 min after administration. Each data point provided represents the mean of six to eight animals, including the respective SEM indicated by the whiskers . Rota-Rod values at the time point at which the greatest sedative responses were observed for each respective combination were used to plot the dose–response curve shown in B . Paired combinations of etomidate and ACEA produced a dose-dependent decrease of time on the Rota-Rod ( P < 0.05). Comparison of curve fits revealed that a sigmoidal dose–response model with variable slope fits best for the combination of ACEA and etomidate ( R 2= 0.7467).