During surgery, both anesthesia and tissue damage cause physiological stress responses in the body. The hypothalamic-pituitary-adrenal (HPA) axis is activated with increased levels of glucocorticoids. After surgical procedures the stress response may be a cause of postoperative morbidity and pre-emptive analgesic treatment can attenuate the stress response during the postoperative period. In laboratory animals, buprenorphine is a commonly used analgesic. Subcutaneous (s.c.) administration of buprenorphine is most common, but oral administration would be preferable in many cases, enabling administration without any handling of the rat.
In this thesis we studied the surgical stress response in laboratory rats during surgery and in the postoperative period, and its modulation by s.c. injection and oral voluntary ingestion (VI) of buprenorphine. Corticosterone levels and the clinical parameters body weight, water intake and behavior were observed. The concentration of buprenorphine in plasma was measured as well as stock-related differences in postoperative recovery.
During surgery and anesthesia there was a higher corticosterone release during a more severe surgery and corticosterone levels were reduced more effectively after buprenorphine treatment than after lidocaine treatment.
Buprenorphine treatment, independent of the route of administration, led to better postoperative recovery in body weight and water intake compared to local anesthetics. VI of buprenorphine resulted in a suppression of plasma corticosterone levels compared to s.c. buprenorphine treatment and treatment with local anesthetics during the first day after surgical catheterization. The corticosterone levels of all buprenorphine treated groups had, by the second postoperative day, reverted to the normal diurnal rhythm of corticosterone secretion. Buprenorphine treatment increased locomotor activity in non-operated rats only. The effect of buprenorphine in operated rats could not be detected via the monitoring of locomotor activity or the time spent resting in the present study.
Treatment with buprenorphine by VI has similar effects on postoperative plasma corticosterone levels in both Wistar and Sprague-Dawley rats. VI of buprenorphine resulted in a buprenorphine concentration in plasma at least as high as by s.c. treatment.
Thus, administration by VI of buprenorphine appears to be an effective stress-reducing method for administrating postoperative analgesia to laboratory rats.