Platelet function in brown bear (Ursus arctos) compared to man

The study objective was to document platelet activity values in brown bears shortly after leaving the den and compare them to platelet function in healthy humans.Blood was drawn from immobilized wild brown bears 7-10 days after leaving the den in mid April. Blood samples from healthy human adults before and after clopidogrel and acetylsalicylic acid administration served as control. We analyzed blood samples by standard blood testing and platelet aggregation was quantified after stimulation with various agonists using multiple electrode aggregometry within 3 hours of sampling.Blood samples were collected from 6 bears (3 females) between 1 and 16 years old and from 10 healthy humans. Results of adenosine diphosphate, aspirin, and thrombin receptor activating peptide tests in bears were all half or less of those in humans. Platelet and white blood cell counts did not differ between species but brown bears had more and smaller red blood cells compared with humans.Using three different tests, we conclude that platelet function is lower in brown bears compared to humans. Our findings represent the first descriptive study on platelet function in brown bears and may contribute to explain how bears can endure denning without obvious thrombus building. However, the possibility that our findings reflect test-dependent and not true biological variations in platelet reactivity needs further studies.Hibernating Scandinavian brown bears (Ursus arctos) stay inside their winter dens for approximately 5-7 months [1,2] and during this hibernation period they do not eat, drink, defecate, urinate or have any physical activity. Despite this, brown bears do not develop deterioration in heart function [3], muscle atrophy [4], osteoporosis (black bear, Ursus americanus, observation [5]), or decubitus ulcer (authors observation). Immobility predisposes humans to thromboembolism [6] but in accordance with findings in other hibernating animals [7] it is unlikely that denning bears develop coa