Melatonin is not stored in platelets.

Background: Melatonin is one of numerous biologically active compounds reported to be stored in platelets. As melatonin is increasingly linked to several diseases, we wanted to confirm the storage of melatonin in platelets using sensitive liquid chromatography in combination with isotope dilution tandem mass spectrometry (LC-MS/MS). The difference between melatonin levels analyzed in platelet-rich plasma (PRP) and platelet-poor plasma (PPP) served as proxy for platelet levels of melatonin.

Methods: Melatonin concentrations were analyzed in PRP and PPP from nineteen healthy volunteers by ELISA and LC-MS/MS. A Wilcoxon signed-rank test was performed to assess if the melatonin levels measured in PRP and PPP were different. Results for melatonin concentrations obtained by LC-MS/MS or ELISA were compared using Passing-Bablok regression.

Results: Comparison of the ELISA with the LC-MS/MS method showed poor agreement for melatonin concentrations in PRP and PPP. No indication was found for storage of melatonin in platelets by either LC-MS/MS or ELISA (P = .89 and P = .53 for the LC-MS/MS and ELISA analysis, respectively).

Conclusion: In this study we could find no evidence for melatonin storage in platelets.