Elevated plasma concentrations of haptoglobin in European brown bears during hibernation

Haptoglobin (Hp), a hemoglobin-binding protein, is known as an acute phase protein and increases during the acute phase of inflammation in most mammals. We reported previously in brown bears that the mean Hp concentrations were higher in blood samples obtained in winter than those in spring. To examine a possible relation of the seasonal variations of Hp to hibernation, in the present study, we measured the plasma concentrations of Hp as well as some other acute phase proteins (α₂-macroglobulin, α₁-antitrypsin, C-reactive protein) in 6 European brown bears (Ursus arctos), from which blood samples were obtained at 5-6 different months of year including February, the time of hibernation. The Hp concentrations showed clear seasonal variations, being highest in February. The α₂-macroglobulin concentrations also showed a similar but much smaller rise in February, but those of α₁-antitrypsin and C-reactive protein did not show any seasonal variations. Our results suggest that the seasonal variation of plasma Hp concentration in brown bears is associated with a hibernation-specific mechanism more than that of acute phase response.