Plasma corticosterone in rats is specifically increased at recovery from propofol anesthesia without concomitant rise of plasma ACTH.

General anesthesia combined with surgery is commonly associated with post-operative stress-response in humans. Effects on the hypothalamic-pituitary-adrenal axis (HPA) during and after anesthesia are correlated with the magnitude of surgery and choice of anesthetics. The aim of our study in rats was to characterize the effects of general anesthesia without any surgery on HPA regulation of corticosterone and adrenocorticotropic hormone (ACTH) secretions. First, to assess whether the acute effects of general anesthesia on corticosterone concentration depend on time of day, rats were anesthetized with propofol at three different Zeitgeber times (ZT6, ZT10, and ZT16; with lights-on and -off at ZT0 and ZT12, respectively). Second, to determine the prolonged effects of general propofol anesthesia on daily corticosterone and ACTH concentrations, rats were anesthetized at ZT16 (4 h after lights-off) and euthanized either 1, 4, 12, 16, 20, or 24 h later. Third, the effects of propofol anesthesia on corticosterone and ACTH secretion were studied in rats instrumented with intracarotid cannulation. This permitted us to examine the individual patterns of corticosterone responses to propofol anesthesia as compared to their respective baseline corticosterone secretion. All of the results obtained showed that general propofol anesthesia, independent of the time-of-day of its administration, induces a significant increase of corticosterone secretion during the early recovery period without effect on ACTH secretion (i.e., no pituitary mediated stress-response).