Comparison of two intravenous infusion schedules for inducing physical dependence upon ethanol in rats

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Male hooded rats were implanted with intravenous (IV) cannulas and housed in operant chambers. The effectiveness of two infusion schedules for producing physical dependence upon ethanol was assessed. Twenty-three rats (12 ethanol, 11 control) were tested under a 4 hr interinfusion schedule (one infusion every 4 hr, around the clock), and 29 rats (15 ethanol, 14 control) were tested under a 2 hr interinfusion schedule. During the dependence induction phase, which lasted for 6 days, the experimental rats received ethanol (30% v/v) at an average daily dose which ranged from 8.4–11.8 g/kg, and the dose administered per infusion was adjusted according to the degree of intoxication of each animal. The pair-fed control subjects received infusions of isocaloric control solutions (either 29% v/v propylene glycol or 31% v/v glycerol). Following the dependence induction phase, ethanol was withdrawn, and withdrawal symptoms were assessed. Blood ethanol levels (BEL) and signs of intoxication were determined through all phases of the experiment. During the dependence induction phase, mortality was close to zero, and weight loss was held to about 10%. Tolerance to ethanol developed in all experimental rats. During the withdrawal period, all ethanol rats developed clear withdrawal symptoms, while control subjects did not. Ethanol elimination rates ranged between 45–50 mg/dl/hr and withdrawal symptoms began when BEL fell below 200 mg/dl, and were severe when BEL approached zero. The 2 hr schedule proved superior to the 4 hr schedule in that it led to greater stability of BEL during dependence induction, and a tendency for the withdrawal reaction to be more severe. These data are important, because they suggest that when physical dependence develops to a given daily dose of ethanol, the resultant withdrawal reaction will be more severe if the dose is administered in such a way so as to maintain highly stable BEL throughout each day of the dependence induction period.