(Table 1) Cortisol concentration in hair of East Greenland polar bears (Ursus maritimus)

To demonstrate the ability to assess long-term hypothalamic-pituitary-adrenocortical (HPA) axis activity in polar bears (Ursus maritimus), a pilot study was conducted in which cortisol concentration was analyzed in hair from 7 female (3-19 years) and 10 male (6-19 years) East Greenland polar bears sampled in 1994-2006. The hair was chosen as matrix as it is non-invasive, seasonally harmonized, and has been validated as an index of long-term changes in cortisol levels. The samples were categorized according to contamination: eight were clean (2 females, 6 males), 5 had been contaminated with bear blood (2 F, 3 M), and 4 with bear fat (3 F, 1 M). There was no significant difference in cortisol concentration between the three categories after external contamination was removed. However, contaminated hair samples should be cleaned before cortisol determination. Average hair cortisol concentration was 8.90 pg/mg (range: 5.5 to 16.4 pg/mg). There was no significant correlation between cortisol concentration and age (p = 0.81) or sampling year (p = 0.11). However, females had higher mean cortisol concentration than males (females mean: 11.0 pg/mg, males: 7.3 pg/mg; p = 0.01). The study showed that polar bear hair contains measurable amounts of cortisol and that cortisol in hair may be used in studies of long-term stress in polar bears.为评估北极熊（Ursus maritimus）下丘脑-垂体-肾上腺（hypothalamic-pituitary-adrenocortical, HPA）轴的长期活性，本研究开展了一项预实验：对1994至2006年间采集的7只雌性（3~19岁）、10只雄性（6~19岁）东格陵兰北极熊的毛发样本中的皮质醇（cortisol）浓度进行了分析。选择毛发作为检测基质，因其具备无创性、采样季节一致性，且已被证实可作为皮质醇水平长期变化的有效指标。本研究按污染情况对样本进行分类：8份为无污染样本（2只雌性、6只雄性），5份被熊血液污染（2只雌性、3只雄性），4份被熊脂肪污染（3只雌性、1只雄性）。去除外源污染物后，三类样本的皮质醇浓度无显著差异，但受污染的毛发样本在开展皮质醇检测前需进行净化处理。毛发皮质醇的平均浓度为8.90 pg/mg（范围：5.5~16.4 pg/mg）。皮质醇浓度与年龄（p=0.81）及采样年份（p=0.11）均无显著相关性；不过雌性北极熊的毛发皮质醇平均浓度显著高于雄性（雌性均值：11.0 pg/mg，雄性均值：7.3 pg/mg；p=0.01）。本研究证实，北极熊毛发中含有可检测的皮质醇，且毛发皮质醇可应用于北极熊长期应激状态的相关研究。