Circadian Variations in Anesthetic Requirement and Toxicity in Rats

TLDR: Circadian variation in cyclopropane toxicity (apneic concentration) was not found, however, calculations of the anesthetic index showed a cyclic pattern similar to that observed for MAC.

Abstract: The effects of circadian rhythm on cyclopropane and halothane requirements (MAC) and cyclopropane toxicity have been investigated at four-hour intervals in rats synchronized to a standard 24-hour day. Longitudinal and transverse determinations in four groups of animals showed characteristic circadian patterns, with the highest values occurring in the early dark (active) period and lowest values occurring in the early light (inactive) period. Differences in MAC were significant (P < 0.05) for each agent, with maximal changes showing 10 to 14 per cent variation from mean values. Circadian variation in cyclopropane toxicity (apneic concentration) was not found. However, calculations of the anesthetic index showed a cyclic pattern similar to that observed for MAC.