The effect of probe depth on histamine levels in humans. In vivo cutaneous microdialysis

Background/aims: Microdialysis technique, for the in vivo estimation of endogenous and exogenous substances in tissues, is gaining increasing use in human experimentation. The cutaneous microdialysis technique has interesting applications in several fields, including the study of skin inflammation and percutaneous absorption. One of the aspects of cutaneous microdialysis which needs clarification is the influence on results of the exact position of the microdialysis probe in the dermis. Methods: In a total material of 67 histamine experiments, probe depth has been measured by the ultrasound technique. In 24 uniform experiments, histamine values at 10-min intervals after probe insertion and prior to other provocation have been analyzed in relation to probe depth. Results: The mean probe depth was 1.1 mm (range 0.8-1.9 mm). In regression analysis of histamine values in 10-min intervals up to 90 min after probe insertion in relation to probe depth, the histamine values were found to be independent of probe depth. This may be due to rapid local diffusion of histamine, together with axon reflex mediated histamine release. Further analysis revealed no correlation between histamine results and the subject's age, sex or presence of atopy. Conclusion: The present results indicate that the exact placement of the microdialysis probe into the dermis is not too critical in experiments where histamine is to be studied. It must be pointed out that the same may not necessarily be true of other inflammatory mediators: for each new target substance and application, the influence of probe placement needs to be considered.