Physiology of the European brown bear (Ursus arctos arctos)

Although the American black (Ursus americanus) and American brown (grizzly) (Ursus arctos horribilis) bears have been the subjects of intensive physiological research, very little so far, has been done to understand the physiology of the European brown bear (Ursus arctos arctos). In our laboratory the research on the physiology of European brown bears started 10 years ago. Between 1987 and 1997, the seasonal changes in physiological indicators such as body temperature (Tb) and blood chemistry were studied in 12 bears under captive conditions in the Zoological Garden of the Department of Biology, University of Oulu, Finland. Changes in the Tb were measured either by using telemetric transmitters or dataloggers implanted into the abdominal cavity under anesthesia. The results show that the Tb decreases during the winter sleep to 3–5°C below the normal level or 37.0–37.5°C. Our bears only slept for just over three months per winter. The winter sleep started in late November/early December and ended in late February/early March. Our results do not support the theory of universal hibernation induction. Plasma from a winter-sleeping bear after injection either into Djungarian hamster (Phodopus sungorus) or laboratory rat did not affect body temperature or diurnal activity of the recipient. The urea concentration during the denning period is only half of that observed in the summer. This decrease during the denning period is in agreement with studies performed on American black and grizzly bears. In sharp contrast to earlier studies performed on the American black bear, our results reveal increases and decreases in the concentration of amino acids supporting the view that the denning bear may be even able to synthesize essential amino acids. The analysis of the total plasma fatty acids show that there may be a trend towards a greater need of unsaturated fatty acids in the denning bear as is the case of true hibernators.