CHANGES IN PLASMA-CORTISOL CONCENTRATIONS IN BITCHES IN RESPONSE TO DIFFERENT COMBINATIONS OF HALOTHANE AND BUTORPHANOL, WITH OR WITHOUT OVARIOHYSTERECTOMY

Changes in plasma cortisol concentrations were assessed in bitches in response to nine treatments: control, anaesthesia, analgesia, analgesi a followed by anaesthesia, anaesthesia followed by analgesia at incuba tion, anaesthesia followed by analgesia at extubation, anaesthesia plu s surgery, analgesia followed by anaesthesia plus surgery, and anaesth esia plus surgery followed by analgesia. The anaesthetic was halothane , the analgesic was butorphanol (0.4 mg kg(-1)) and the surgery was ov ariohysterectomy. Blood samples, for plasma cortisol assays, were take n regularly from before treatment for five hours and then again after 24 hours. A small transient rise in plasma cortisol concentration in t he control group was attributed to mild distress associated with novel experience. A more pronounced and protracted rise in cortisol concent ration in the analgesia group was ascribed to a dysphoric state of bit ches under the influence of the agonist-antagonist butorphanol. Haloth ane anaesthesia alone resulted in no change in plasma cortisol concent ration. When butorphanol was given after anaesthesia was induced or wh ile the animal was still under the influence of anaesthesia (immediate ly after tracheal extubation), there was no immediate rise in plasma c ortisol concentration and low concentrations were maintained for up to 60 minutes after halothane withdrawal. A marked rise in plasma cortis ol concentration, which was sustained above pretreatment values for at least five hours, occurred in all surgery groups. Giving intravenous butorphanol 30 minutes prior to surgery had no effect on the surgicall y-induced rise in plasma cortisol concentration and no effect on the p ostsurgical plasma cortisol concentration. In contrast, butorphanol gi ven at extubation did reduce plasma cortisol concentrations during the postsurgical period. These observations did not support the hypothesi s that preoperative use of butorphanol would reduce the cortisol respo nse after surgery under halothane anaesthesia.