Effects of hibernation on blood clot formation and fibrinolysis in 13-lined ground squirrels

Abstract

Thirteen-lined ground squirrels (Ictidomys tridecemlineatus) enter hibernation to survive periods of low temperatures and scarce food availability. Typical ground squirrel hibernation is characterized by prolonged periods of torpor with decreased physiological activity, interrupted every few weeks by brief interbout arousals (IBA). Decreased blood flow during torpid states should increase the risk of stasis-induced blood clots. However, ground squirrels have adapted to survive repeated bouts of torpor and IBA without forming lethal blood clots. Although ground squirrels have developed antithrombotic adaptations to avoid lethal blood clots during hibernation, whether these adaptations cease all ability to form blood clots remains unknown. Thrombin-antithrombin complex, was significantly reduced (p<0.05) during hibernation, and D-dimer level remained unchanged throughout the annual cycle. Tissue plasminogen activator complexed with plasminogen activator inhibitor to total plasminogen activator inhibitor ratio, was significantly increased (p<0.05) during hibernation. Protein level of plasminogen activator inhibitor was significantly reduced (p<0.05) during hibernation. These data suggest that ground squirrels do not form blood clots during hibernation, in part due to suppression of coagulation, Furthermore, hibernators sustain hyperfibrinolytic states even in the absence of blood clots, Although likely, any clots formed during hibernation may be less resistant to fibrinolytic degradation.