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Environmental changes result in physiological responses of organisms, which can adversely affect population dynamics and reduce resistance to disease. These changes are expressed in chronic levels of stress. Measuring glucocorticoid (GC) concentration in faeces is a non-invasive method for monitoring stress in wildlife. Metabolism and excretion of steroids differ significantly between species, therefore, non-invasive methods must be physiologically validated for each species. Koalas (Phascolarctos cinereus) are declining in numbers through much of their range. The role of chronic stress in koala populations has not been identified. Prior to the assessment of faecal GC in wild koala populations, the excretion timing and concentrations of GCs need to be determined. In this study, we assessed a method for identifying and measuring concentrations of GC metabolites in faecal pellets of captive koalas following adrenocorticotropic hormone (ACTH) treatment. The results show that an elevation in plasma cortisol concentration, using sustained release ACTH, results in elevated faecal cortisol/cortisol metabolites. Taking into account the excretion time lag, an increase in faecal cortisol metabolite concentrations (FCM) corresponds to the release of GCs from the adrenal cortex at least 36 hrs prior. Calculations of steroid partitioning of plasma cortisol showed that ACTH stimulated values were significantly different to the control values for free, CBG bound and albumin bound cortisol concentrations. This study validates the use of faecal cortisol analysis to assess the activity of the hypothalamo-pituitary-adrenocortical axis in freshly-collected koala faecal pellets and indicates the method should be suitable to assess the adrenocortical status of koalas in wild populations.

Citation

Nicole Ashley Davies, Amber Gillett, Clive McAlpine, Leonie Seabrook, Greg Baxter, Daniel Lunney, Adrian Bradley. The effect of ACTH upon faecal glucocorticoid excretion in the koala. The Journal of endocrinology. 2013 Jul 9


PMID: 23838520

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