Background: Hormones oscillate in circadian and ultradian rhythms. Single time point samples are difficult to interpret and high frequency measurements are time consuming, expensive and invasive. We developed a minimally invasive technique of ambulatory, automated microdialysis. This allows frequent 24-hour sampling of interstitial fluid while participants continue normal daily activities.
Methods: Healthy volunteers (age 1868, no regular medications, no active medical conditions, BMI 1629) were recruited for 24-hour hormone profile analysis. A 20 kDa linear microdialysis sampling catheter was inserted in abdominal subcutaneous tissue. Catheters were perfused at 1 microl/min using a portable CMA107 microdialysis pump attached to our novel fraction collector (U-RHYTHM) worn in an elasticated waist band. Microdialysate samples within the fraction collector were separated by air bubble every 20 minutes. During sampling, participants were free to continue their normal routine. Multiplex analysis of steroid concentrations was achieved using triple quadrupole mass spectrometry.
Results: We present 24-hour profile data for 10 participants. 72 consecutive 10 microL samples were analysed for each participant. The following steroids are presented: cortisol (F), cortisone (E), aldosterone (A), dehydroepiandrosterone sulfate (DHEAS), corticosterone (CCS), 18-OH-cortisol (18-OHC), 18-OH-corticosterone (18-OHCCS). All 24-hour profiles demonstrated circadian and/or ultradian rhythms.
Conclusions: Ambulatory microdialysis using U-RHYTHM in combination with high precision mass spectrometry can reliably and accurately detect dynamic fluctuations in steroid physiology during normal daily activities, without the need for hospitalisation.