Hibernating mammals have developed many physiological adaptations to extreme environments. During hibernation, 13-lined ground squirrels ( Ictidomys tridecemlineatus) must suppress hemostasis to survive prolonged body temperatures of 4–8°C and 3–5 heartbeats per minute without forming lethal clots. Upon arousal in the spring, these ground squirrels must be able to quickly restore normal clotting activity to avoid bleeding. Here we show that ground squirrel platelets stored in vivo at 4–8°C were released back into the blood within 2 h of arousal in the spring with a body temperature of 37°C but were not rapidly cleared from circulation. These released platelets were capable of forming stable clots and remained in circulation for at least 2 days before newly synthesized platelets were detected. Transfusion of autologous platelets stored at 4°C or 37°C showed the same clearance rates in ground squirrels, whereas rat platelets stored in the cold had a 140-fold increase in clearance rate. Our results demonstrate that ground squirrel platelets appear to be resistant to the platelet cold storage lesions observed in other mammals, allowing prolonged storage in cold stasis and preventing rapid clearance upon spring arousal. Elucidating these adaptations could lead to the development of methods to store human platelets in the cold, extending their shelf life.
Thirteen‐lined ground squirrels (Spermophilus tridecemlineatus)experience a dramatic decrease in body temperature and heart rate during hibernation. These extreme conditions would likely cause human platelets to clot due to low blood flow rate and pressure. We have found that ground squirrels drastically decrease their circulating platelet and leukocyte counts during hibernation, likely to reduce the risk of clotting. Previous research has shown that chilled human and mouse platelets are rapidly cleared from circulation. However, upon arousal from torpor, ground squirrel platelets are rapidly released into circulation from their storage site in the spleen and persist for several days until new platelet synthesis begins. Flourescently labeled platelets were incubated at 4°C or 37°C and reinjected into autologous ground squirrels. Clearance rates of both warm and chilled platelets were the same. Identification of protective factors that prevent rapid clearance of chilled platelets may ultimately lead to the ability to refrigerate human platelet concentrates. This work was supported by an NIH R15 grant.
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