Progesterone decreases sevoflurane requirement in male mice: a dose-response study.

BACKGROUND Progesterone has long been known to have central effects, by reduced anaesthetic requirements as measured by minimum alveolar concentration (MAC) in various settings. However, other studies have contradicted these findings. Therefore, we compared the effect of progesterone on anaesthetic requirements in a mouse model. METHODS Male C57BL/6 mice were treated with either progesterone (37.5 or 75 mg kg(-1)) or the olive oil vehicle, 1 h before each experiment. Animals were placed in a revolving cylinder (4 rev min(-1)) and supplied with oxygen and stepwise increasing concentrations of sevoflurane. The number of complete rollovers during revolution of the chamber was counted as a measure of anaesthetic requirement. RESULTS S.C. administration of progesterone 75 mg kg(-1) significantly reduced sevoflurane requirement (P<0.0001). Progesterone 37.5 mg kg(-1) did not change sevoflurane requirement. CONCLUSIONS We conclude that administration of exogenous progesterone injection at higher concentrations decreases anaesthetic requirement as defined by rolling response.