Remnants of stress hormones: Measurement and biological activity

Möstl, E.

Department of Biomedical Sciences/Biochemistry; University of Veterinary Medicine, Vienna; e-mail: erich.moestl@vetmeduni.ac.at

The front-line hormones of the body to overcome stressful events are the glucocorticoids and catecholamines. The term glucocorticoid covers a group of substances which bind to the glucocorticoid receptors. Most of these substances are produced by the adrenal glands, but other organs like the lymphoid tissues, the digestive tract or the skin can also form cortisol or corticosterone.

In many species glucocorticoid concentrations in blood show a circadian rhythm, but ultradian patterns also play a role in the effects of these hormones. Monitoring short term variations demands frequent blood sampling, which will increase the stress level in non-habituated animals. Alternatively, glucocorticoids can also be measured in saliva. Before elimination via urine and faeces the glucocorticoids are metabolized into a multitude of metabolites, and in the gut, microorganisms are further converting these steroids. Therefore analytical tools are needed to detect the remnants. These substances can be measured either by immunoassays or physical/chemical methods such as chromatography plus mass spectroscopy. The first challenge is to find the best matrix for a given aim to analyse the stress hormone metabolites and to find a well-suited detection system. The second challenge is to select the timing of sample collection and the storing system, esp. in field endocrinology. Different immunoassays have unequal cross-reactions with glucocorticoid metabolites. The specificity of an assay can be validated using immunograms and results have to be considered as “equivalents” of the standard used.

Concerning the biological activity of the glucocorticoid metabolites, only limited information is available. A part of the glucocorticoids undergo side chain cleavage and resulting metabolites act in fish as androgens, as they resemble 11-ketotestosterone, a dominating fish androgen. One of the cortisol metabolites (11-oxoaetiocholanolone) is described as a putative pheromone. Therefore, the concentrations of some glucocorticoid metabolites in effluents of areas of high animal density and of sewage treatment plants may have some importance for aquatic organisms.