Endocrine Abstracts

Introduction: For diagnostic purposes, total-testosterone levels are generally assessed in plasma. However, as the primary site of action of testosterone is in tissue, evaluation of the distribution of testosterone in tissue fluids could give enhanced insight into the (patho)physiological state. Clinical microdialysis allows for sampling at tissue level based on diffusion.

Objective: To compare the increase in testosterone levels in tissue and plasma after cutaneous administration of testosterone.

Methods: A CMA20 microdialysis probe was continuously perfused with Ringer’s lactate containing 0.6 nmol/l D5-testosterone as internal reference. A sample interval of 15 min was used, with a perfusion rate of 10 ml/min. Microdialysis was performed on the vastus lateralis muscle in two healthy male volunteers for 4 h, preceded by a 1h run in period. Additionally, blood specimens were drawn in each interval. After one hour, 100 mg testosterone gel was applied to the skin of the back in an attempt to vary plasma and tissue testosterone levels. Testosterone was analyzed using a highly sensitive assay involving derivatization and ID-LC-MS/MS.

Results: Testosterone profiles in the collected microdialysis and plasma samples from both volunteers were comparable. Testosterone levels increased after cutaneous administration, in both microdialys fluid (70%) and plasma (60%).

Conclusion: The initial results of clinical microdialysis are promising. Low testosterone levels as well as increased concentrations after supplementation could be reliably detected. Further research is necessary to thoroughly evaluate the microdialysis procedure. Hopefully, in vivo experiments in the near future will enrich our knowledge about testosterone at the tissue level.