Endocrine Abstracts

In order to understand the significance of circadian and ultradian hormonal rhythms in man, both in health and disease, it is essential to be able to obtain multiple samples over extended periods, especially during the hours of sleep. The human automated blood sampling (HABS) system reported by Henley and colleagues can achieve this but is recommended for use in the setting of a clinical investigation unit which is its major drawback. For many diagnostic and scientific questions, the most meaningful physiological setting to look at homeostatically important hormones is a subject’s home setting. We have now developed an alternative approach to measure glucocorticoid hormones using the technique of subcutaneous microdialysis. This has the additional advantage that it measures the level of active free cortisol as opposed to the total cortisol levels measured in whole blood of which approximately 90% is bound to carrier proteins. Since only the free unbound cortisol has access to tissues and their receptors these are the levels that are physiologically important for glucocorticoid signalling. The technique of microdialysis combined with a novel miniaturised sampling system provides the ability to collect multiple samples automatically without the need for venous access. As part of the validation of this technique, serum samples and corresponding microdialysate samples from either the subcutaneous tissue compartment alone or both subcutaneous tissue and intravenous compartment were collected every 10 min from 1000 to 1400 h in healthy male volunteers aged 19–28 years. Preliminary results confirm that free cortisol is detectable using this technique in both the body compartments and that free cortisol levels reflect spontaneous changes in serum total cortisol measured during the study period. Our early results indicate the potential of this system as a unique tool in research and in clinical diagnosis.

Declaration of funding: This work was carried out with financial support from the European Union – FP7 grant to OPTIMI.