Methods for determining cortisol concentrations in animals

Abstract

The steroid hormone cortisol is the end product of the hypothalamic-pituitary-adrenal (HPA) axis. Recently, cortisol has been considered as a potential biomarker for identifying stress, because it is directly related to the body›s response. The most common methods for determining endocrine status, including cortisol, are enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA), as they are the most reliable and have high sensitivity. Cortisol levels are determined mainly in blood, saliva, serum and urine. The concentration of this hormone in these samples is related to the circadian rhythm and fluctuates throughout the day. Therefore, samples of this biomaterial allow the analysis of acute dynamic changes in cortisol. The effects of chronic stress require assessment of long-term stress levels. Hair (fur) cortisol concentrations are increasingly used as a biomarker of long-term stress. Hair cortisol analysis has thus been a major methodological advance because it provides retrospective assessment of cumulative levels over long periods of time (from days to months). Over the past decade, the validity of hair (fur) cortisol levels as an indicator of long-term levels has been established. In addition, this material is the most stable over time and resistant to environmental influences. Measuring hair cortisol levels is an innovative method for determining long-term increases in cortisol levels, independent of many methodological difficulties and not associated with other matrices. Interest in hair as an object of endocrine activity is due to various unique features that provide many advantages over other biomaterials.