Induction of steady-state blood alcohol levels: application to the study of within-session alcohol tolerance in rats

The study of within-session alcohol tolerance in the rat has been hampered by methodological difficulties related to the measurement of dependent variables at predictable blood alcohol concentrations (BAC) during a single session of alcohol exposure. This study characterizes a method for maintaining steady-state blood alcohol levels over several hours in the rat, referred to as the "alcohol clamp." Wistar rats were implanted with an indwelling catheter in the carotid artery for blood sampling and another in the external jugular vein for alcohol infusion. To clamp BAC at a predetermined level, rats first were infused with a priming dose of alcohol to establish the desired or "target" BAC, followed by a continuous infusion of alcohol at a rate equal to that of alcohol metabolism in the rat. This maintained BAC at a constant level over time. BACs of 100, 200, or 300 mg% were maintained over several hours in separate groups of rats. The alcohol clamp was applied to the study of acute (within-session) alcohol tolerance in rats selectively bred for high and low alcohol drinking. Alcohol-induced hypothermia was used to index tolerance, and within-session alcohol tolerance was defined as a return of body temperature toward baseline during the course of the alcohol infusion while BAC was maintained at a constant level. The continuous alcohol infusion procedure maintained BAC in a steady state throughout the 3 hr alcohol infusion session at each of the three target BAC levels. Alcohol infusion induced a drop in body temperature, followed by a return of temperature toward baseline during the course of infusion, which indicated the development of within-session alcohol tolerance. The continuous alcohol infusion procedure (alcohol clamp) maintained BAC in a steady state, both within and between subjects, across a wide range of blood alcohol levels. The alcohol clamp appears to be a useful tool for subsequent studies of within-session alcohol tolerance in the rat.