Rapid development of tolerance to the hypothermic effect of ethanol in mice.

The hypothermic response to i.p. injection of ethanol (2.0-4.0 g/kg) in mice was found to be attenuated by a single equivalent ethanol injection given 24 hr earlier. The diminished hypothermic response was not an artifact since it could not be attributed to changes in body weight and was independent of familiarity with test environment and procedures. A parallel shift in the dose-response curve was found. It appears, therefore, that the reduced change in body temperature is indicative of tolerance. If the second ethanol injection was given 48 or 72 hr later, tolerance could no longer be seen. With injections spaced 24 hr apart, a third administration of ethanol did not further increase the tolerance seen after the second injection. Since blood ethanol levels did not differ in tolerant and nontolerant mice, and since tolerance was already present 10 min after the second ethanol injection, a functional rather than a metabolic tolerance is likely.