ACUTE TOLERANCE INDICES FOR PENTOBARBITAL IN MALE AND FEMALE RATS

¹ Departments of Anesthesiology and of Physiology and Pharmacology, Wayne State University School of Medicine, Detroit, Michigan

An index of acute anesthetic tolerance potential is proposed based on the calculated potency of a barbiturate in the tolerant rat compared to that in the pretolerant rat. This relative potency is estimated from the regression of log dose upon log sleeping time in the tolerant and pretolerant state. Maximal acute tolerance is induced by repeatedly administering the AD99.9 (anesthetic dose) of the drug on a schedule providing the greatest reduction in duration of anesthesia in the shortest time. This "acute tolerance index" with its 95% confidence limits was found to be 0.595 (0.500-0.709) in the adult female rat and 0.886 (0.825-0.951) in the adult male rat. Employing similar calculations, the potency of pentobarbital in the adult male rat, relative to the adult female, was found to be 0.403 (95% limits of 0.360-0.451) in pretolerant animals and 0.581 (95% limits of 0.517-0.653) in tolerant animals.