Studies on acute tolerance to ethanol in the abstinence period after long-term barbital treatment in the rat.

Male rats were treated with sodium barbital in the drinking water for 18 weeks. The average weekly dosage was around 215 mg/kg in groups 1, 3 and 5. Groups 2, 4 and 6 were controls. Every week in the abstinence period after the barbital treatment the sensitivity to hexobarbital was tested with a threshold method after three different pretreatments. These pretreatments consisted of saline (groups 1 and 2) and ethanol (2.0 g/kg intraperitoneally) given either 0.25 hr (groups 3 and 4) or 2.5--3 hrs (group 5 and 6) prior to the hexobarbital test. Tolerance seen as a difference in the sensitivity to hexobarbital between groups 1 and 2 (saline pretreatment) were found on day 1, 8, 22 and 36 in the abstinence period. In groups 3 and 4 (tested 0.25 hr after ethanol) a tolerance was found on day 1 and 15. In groups 5 and 6 (tested 2.5--3 hrs after ethanol) a tolerance was only found on day 1. An acute tolerance to ethanol in the controls (seen as a difference between groups 4 and 6) was always recorded. Since tolerance in group 1 was not always accompanied by a tolerance in group 3, an acute tolerance to ethanol is unlikely as an unitary explanation to the tolerance induced by the barbital treatment, which instead seem to be part of much more complex changes. The acute tolerance to ethanol was influenced by the weekly administrations of ethanol used in the tests of the controls (groups 4 and 6) which means that acute tolerance could be one participant in these more complex changes.