Assessment of the development of tolerance to ethanol using multiple measures.

Development of tolerance to ethanol was examined using a motor coordination test, startle response, and rectal temperature in rats chronically treated with ethanol (8-11 g/kg/day), equicaloric dextrin maltose (DM) or water. A 2.0 g/kg test dose resulted in 92, 48, and 2.7% depression from baseline of motor coordination test performance, startle response, and rectal temperature, respectively, on the first test day. There was complete tolerance to the hypothermic effect of this dose of ethanol on the 9th day of treatment while 17 days of treatment were required to achieve total tolerance on dowel test but still did not produce full tolerance on the startle response. Measurement of blood ethanol concentration indicated no significant changes in the rate of ethanol disappearance. Therefore the observed decrease in sensitivity to ethanol represents functional tolerance. These results indicate tolerance to ethanol develops at different rates depending on the measures employed to evaluate it.