Analysis of endogenous cortisol concentrations in the hair of rhesus macaques

Short-term changes in activity of the hypothalamic–pituitary–adrenocortical (HPA) system are routinely assessed by measuring glucocorticoid or metabolite concentrations in plasma, saliva, urine, or feces. However, there are no current methods for determining long-term (i.e., weeks or months) activity of this system. Herein, we describe the development and validation of a simple procedure for measuring cortisol concentrations in the hair of rhesus macaques. This procedure involves two brief isopropanol washes of the hair strands to remove surface contaminants, subsequent powdering of the washed and dried hair, a 24-h methanol extraction followed by evaporation of the solvent and reconstitution of the extract in assay buffer, and finally analysis of the extracted cortisol by a sensitive and specific enzyme immunoassay. Our results confirm the specificity of the procedure for cortisol, show that proximal and distal segments of hair do not differ in their cortisol concentration, and demonstrate that a significant and prolonged stressful experience produces a significant increase in hair cortisol. This new procedure should be valuable for assessing baseline HPA activity in nonhuman primates (and, with appropriate validation, in other species as well) over relatively long periods of time, and also for monitoring chronic stress that might be associated with various experimental manipulations.