Endocrine Abstracts

Sleep and cortisol cycles have a complex inter-relationship that is not fully understood. Slow wave sleep appears to have an inhibitory effect on cortisol production but the effect of other stages is not so clear. From diseases, such as Addisons disease and Cushings syndrome, we know that cortisol levels have an impact on the quality of sleep. In insomnia and depression, both sleep and cortisol is altered.

To investigate this relationship properly a minimally invasive method of venepuncture is needed to reduce the impact of blood taking upon cortisol secretion and sleep. An automated sampling machine has been developed to minimise interference with study subjects when taking blood samples. The human automated blood sampling machine (HABS) can be programmed to take small volume of blood at regular intervals over several hours e.g. 1 ml samples at 10-min intervals for 12 h. The advantage of using HABS is minimal disruption for study subjects, exact timing of samples and the small volumes of blood taken.

Six healthy subjects were recruited to the study. Local ethics committee approval had been obtained for the study. On arrival at the sleep laboratory, the subject was attached to the polysomnography equipment and cannulated. They were then connected to the HABS machine for overnight blood sampling; samples were taken every 10 min. All the subjects were woken at seven am and had salivary cortisol taken on waking and 30 min later. The HABS machine continued sampling for thirty minutes after waking.

The results obtain showed that using HABS is a reliable and minimally disruptive method of obtaining blood samples that did not interfere with the recording of sleep. Future uses for the machine are the investigation of the cortisol circadian rhythm in insomnia and depression and the hypothalamic–pituitary–adrenal axis.