Blood clotting behavior is innately modulated in Ursus Americanus during early and late denning relative to summer months

Abstract

Remarkably, American black bears (Ursus americanus) are capable of varying their heart rates to coincide with their breathing, creating pauses of 30 s or more, yet they do not appear to suffer from embolic events. We evaluated some features of the clotting cascade of black bears, providing novel insights into the underlying mechanisms they evoke for embolic protection during hibernation. We measured activated clotting time, prothrombin time and activated partial thromboplastin time during early denning (December), late denning (March) and summer (August). Activated clotting time during early hibernation was ∼3 times longer than that observed among non-hibernating animals. Clotting time was reduced later in hibernation, when bears were within ∼1 month of emerging from dens. Prothrombin time was similar for each seasonal time point, whereas activated partial thromboplastin time was highest during early denning and decreased during late denning and summer. We also examined D-dimer concentration to assess whether the bears were likely to have experienced embolic events. None of the nonparturient bears exceeded a D-dimer concentration of 250 ng ml −1 (considered the clinical threshold for embolism in mammals). Our findings suggest there is unique expression of the clotting cascade in American black bears during hibernation, in which extrinsic pathways are maintained but intrinsic pathways are suppressed. This was evaluated by a significant difference between the activated clotting time and activated partial thromboplastin time during the denning and non-denning periods. These changes are likely adaptive, to avoid clotting events during states of immobilization and/or periods of asystole. However, an intact extrinsic pathway allows for healing of external injuries and/or foreign body responses.

Development and utilization of implantable cardiac monitors in free-ranging American black and Eurasian brown bears: system evolution and lessons learned

“…Further, through these experiences, we observed first-hand that black bears elicit rapid wound healing abilities during hibernation. More specifically, we found little or no evidence post-rejection as to the prior existence of implants due to tissue remodeling at the implant location [23,24,34,35]. High rejection rates in our study, and another study using implanted telemetry devices in black bear cubs [35], led the authors to question the practicality of implanted devices in free-ranging bears.…”

Novel treatment strategies for chronic kidney disease: insights from the animal kingdom

“…Nevertheless, hibernating bears tolerate extended periods of an extremely low heart rate (~10 beats/min) (214) without developing congestive heart failure, atherosclerosis (215) thromboembolic events or cardiac dilation; which are common features in CKD. The protection against vascular disease may in part be mediated by changes in the coagulation pathway, in which traditionally intrinsic cascades (initiated when blood comes in contact with exposed collagen from damaged endothelial cells) are suppressed and extrinsic tissue factor pathways (initiated by vascular wall trauma) are maintained, to prevent thromboembolic events while enabling external injuries to be healed (216).…”

An engineering perspective on the development and evolution of implantable cardiac monitors in free-living animals

“…In addition to applications relating to conservation and management, opportunities for applying knowledge gained about the unique physiologies of bears to human medicine is an area of increased interest by our team and other researchers. Some of the potential applications to human medicine relating to the physiology of bears, as well as other species, include stroke prevention, elimination of muscle disuse atrophy, treatments for diabetes, heart failure, kidney disease, osteoporosis, respiratory conditions, pre-conditioning organs for transplantation and many others [55][56][57][58][59][60][61][62][63].…”